tag:theconversation.com,2011:/uk/topics/sun-2039/articlesSun – The Conversation2024-03-27T17:09:15Ztag:theconversation.com,2011:article/2258662024-03-27T17:09:15Z2024-03-27T17:09:15ZThe April 8 eclipse provides a rare opportunity to witness the sun’s superhot corona<figure><img src="https://images.theconversation.com/files/584383/original/file-20240326-16-cpzqx3.jpg?ixlib=rb-1.1.0&rect=0%2C2%2C1888%2C1057&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The corona of the sun can be clearly seen in this image taken in 2007.</span> <span class="attribution"><a class="source" href="https://images.nasa.gov/details/PIA09320">(NASA/JPL-Caltech/NRL/GSFC)</a></span></figcaption></figure><p>Being within a narrow path across Mexico, the United States and eastern Canada on April 8 will give a rare chance to see the hottest thing any human ever sees: the corona surrounding the sun.</p>
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Read more:
<a href="https://theconversation.com/on-april-8-2024-parts-of-ontario-quebec-the-maritimes-and-newfoundland-will-see-a-total-eclipse-of-the-sun-heres-how-to-get-ready-for-it-203382">On April 8, 2024, parts of Ontario, Québec, the Maritimes and Newfoundland will see a total eclipse of the sun. Here's how to get ready for it.</a>
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<p>The word “corona” means “crown” — during the eclipse, it becomes visible, and streaming plasma leaving the sun appears in amazing patterns.</p>
<p>This outer atmosphere shines with a strange whitish light, and is safe to look at once the bright surface of the sun is fully obscured. However, it is not safe to look at partial phases of the eclipse without <a href="https://theconversation.com/total-solar-eclipses-while-stunning-can-damage-your-eyes-if-viewed-without-the-right-protection-221381">suitable eye protection</a> such as an approved filter or a <a href="https://svs.gsfc.nasa.gov/14391/">shadow box</a>. </p>
<p>Humankind has been awed by this spectacle <a href="https://www.wired.com/2008/05/may-28-585-bc-predicted-solar-eclipse-stops-battle/">for a very long time without understanding it</a>. Astronomers now know the sun’s corona is heated to up to <a href="https://www.nasa.gov/science-research/heliophysics/nasas-parker-solar-probe-and-the-curious-case-of-the-hot-corona/">two million degrees Kelvin</a>, numerically almost equivalent to Celsius for such high temperatures. </p>
<p>What astronomers haven’t figured out yet is why the corona is so hot.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/ykkrf87WsLI?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">NASA scientists describe photographing the sun’s corona during the 2015 eclipse.</span></figcaption>
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<h2>Heat and density</h2>
<p>The surface of the sun has a temperature of <a href="https://scied.ucar.edu/learning-zone/sun-space-weather/surface-of-the-sun">only about 5,800 kelvins</a> (5,500 C). The reason that we can safely look at the corona but must avoid looking at the surface has to do with density: <a href="https://spaceplace.nasa.gov/sun-corona/en/">the corona is very thin</a>, and most of the light we see is reflected sunlight from the surface. </p>
<p>The sun’s surface has enough density that, at its temperature, it emits about <a href="https://www.pveducation.org/pvcdrom/properties-of-sunlight/solar-radiation-in-space">65 megawatts for each square meter</a>. Even diluted by <a href="https://earthsky.org/space/what-is-the-astronomical-unit/">distance from the sun of 150 million kilometres</a>, this is enough to cause immediate eye damage.</p>
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Read more:
<a href="https://theconversation.com/total-solar-eclipses-while-stunning-can-damage-your-eyes-if-viewed-without-the-right-protection-221381">Total solar eclipses, while stunning, can damage your eyes if viewed without the right protection</a>
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<p>Since the corona is such thin gas, despite its high temperature, it does not emit nor reflect much light. For this reason, we can see it only when the body of the sun is completely blocked by the moon. Otherwise the scattered light in our atmosphere completely overwhelms it.</p>
<p>The mystery of the corona’s heat <a href="https://www.americanscientist.org/article/revealing-the-true-solar-corona">puzzled 19th-century astronomers</a>. At the time, new instruments had been developed to study <a href="https://www.azooptics.com/Article.aspx?ArticleID=1984">the composition of celestial bodies</a>.</p>
<p>In 1704, Sir Isaac Newton had discovered that “white” light could be split into colors, a result <a href="https://library.si.edu/digital-library/book/optickstreatise00newta">published in <em>Opticks</em></a>. Unfortunately, his basic views about light were wrong and likely set back the development of optical science 100 years! </p>
<p>Only in the early 1800s were instruments developed, largely setting the stage for the <a href="https://www.zeiss.com/corporate/en/about-zeiss/past/history/locations.html">immensely profitable German optical industry</a>. This allowed scientists to find out what materials were made of by the light they emitted when heated. </p>
<p>A staple of such studies was the <a href="https://www.britannica.com/science/Bunsen-burner">Bunsen burner</a>, originally developed not to have a colour like other flames do.</p>
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<a href="https://images.theconversation.com/files/582669/original/file-20240318-16-fmoksh.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="a black circle surrounded by wispy white light against a navy background" src="https://images.theconversation.com/files/582669/original/file-20240318-16-fmoksh.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/582669/original/file-20240318-16-fmoksh.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=430&fit=crop&dpr=1 600w, https://images.theconversation.com/files/582669/original/file-20240318-16-fmoksh.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=430&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/582669/original/file-20240318-16-fmoksh.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=430&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/582669/original/file-20240318-16-fmoksh.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=540&fit=crop&dpr=1 754w, https://images.theconversation.com/files/582669/original/file-20240318-16-fmoksh.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=540&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/582669/original/file-20240318-16-fmoksh.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=540&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">A total solar eclipse in 2015 over Svalbard, Norway, reveals the streaming shapes in the solar wind pillars.</span>
<span class="attribution"><span class="source">(M. Druckmüller, S. Habbal, P. Aniol, P. Štarha)</span></span>
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<h2>Photography and astrophysics</h2>
<p>The parallel development of photography also helped <a href="https://history.aip.org/exhibits/cosmology/tools/tools-spectroscopy.htm">astronomy to turn into the science of astrophysics</a>, and the sun was an ideal first target for early instruments due to being very bright. </p>
<p>During the solar eclipse of 1868, emissions like the bright red known to be <a href="https://skyandtelescope.org/observing/guide-to-observing-the-sun-in-h-alpha092321050923/">from hydrogen were observed</a>. But when this light was broken down with a spectroscope, it also showed a yellow light that had never been observed on Earth. </p>
<p>This was determined to be a new element, named for its association with the sun (Greek <em>helios</em>). Only in 1895 was helium found on Earth, and in the strangest of places: <a href="https://www.smithsonianmag.com/history/how-scientists-discovered-helium-first-alien-element-1868-180970057/">radioactive ores</a>. </p>
<p>Almost all helium now used on Earth comes from natural gas fields, where it is trapped as it comes up from uranium and other decaying radioactive ores. The helium in the sun later became strong evidence for the Big Bang, in which the first nuclei, which were hydrogen, quickly underwent nuclear fusion to produce helium, but its discovery in the sun set the stage for expecting new elements there.</p>
<h2>A new mystery</h2>
<p>Once spectroscopy developed further in the late 19th century, indeed another mystery arose. Many elements had been discovered on Earth and put in systematic order by Russian chemist Dmitri Mendeleev as the “<a href="https://pubchem.ncbi.nlm.nih.gov/periodic-table">periodic table</a>.”</p>
<p>Surprisingly, many elements were also detected in solar spectra, usually when they absorbed specific wavelengths from the pure light coming from deep layers in the sun, <a href="https://imagine.gsfc.nasa.gov/science/toolbox/spectra1.html">leaving absorption lines</a>. Although the sun is made mostly of hydrogen and helium, these are not prominent in its spectrum. </p>
<p>However, in the corona, completely unknown lines were found. Following the lead of helium, it was felt that the sun must contain an element never observed on Earth, <a href="https://sunearthday.nasa.gov/2006/locations/coronium.php">promptly dubbed coronium</a>. Only in the 1940s was it realized that the emissions actually came from familiar elements, including iron. These were not initially recognized due to being highly stripped of the normal number of electrons going around their nuclei (normally 26 in iron), indicating extreme temperatures that rip atoms apart. </p>
<p>Even stranger, the further out one observed from the sun, the hotter the corona became.</p>
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<a href="https://images.theconversation.com/files/582445/original/file-20240318-20-t6q0rt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="a black circle surrounded by wisps of red and green" src="https://images.theconversation.com/files/582445/original/file-20240318-20-t6q0rt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/582445/original/file-20240318-20-t6q0rt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=441&fit=crop&dpr=1 600w, https://images.theconversation.com/files/582445/original/file-20240318-20-t6q0rt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=441&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/582445/original/file-20240318-20-t6q0rt.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=441&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/582445/original/file-20240318-20-t6q0rt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=554&fit=crop&dpr=1 754w, https://images.theconversation.com/files/582445/original/file-20240318-20-t6q0rt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=554&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/582445/original/file-20240318-20-t6q0rt.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=554&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">The 2015 eclipse imaged in the light given off by highly ionized iron. The red indicates a temperature about one million degrees C, green about two million degrees C.</span>
<span class="attribution"><a class="source" href="https://doi.org/10.3847/2041-8213/abe775">(SOURCE)</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
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<h2>Solar winds and weather</h2>
<p>In the late 1950s, the physicist Eugene Parker found that such high temperatures for the solar corona meant that it could not be static: it had to <a href="https://news.uchicago.edu/explainer/what-is-solar-wind">be blowing off into space</a>. This prediction was verified by <a href="http://www.phy6.org/Education/whsolwi.html">spacecraft measurements in 1959</a>. </p>
<p>Since then, we have known that there is a solar wind, and that the magnetic field shown by coronal structures is carried off into space with it. The solar wind can bring energy to Earth, which penetrates near us when the magnetic field is opposed to that of our planet, bringing auroras and potentially hazardous “<a href="https://theconversation.com/space-weather-is-difficult-to-predict-with-only-an-hour-to-prevent-disasters-on-earth-159895">space weather</a>.”</p>
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Read more:
<a href="https://theconversation.com/larger-and-more-frequent-solar-storms-will-make-for-potential-disruptions-and-spectacular-auroras-on-earth-219183">Larger and more frequent solar storms will make for potential disruptions and spectacular auroras on Earth</a>
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<p>NASA’s <a href="https://science.nasa.gov/mission/parker-solar-probe/">Parker Solar Probe</a> is now nearing the inner regions of the corona, still trying to determine the exact origins of the solar wind. Parker, who passed away in 2022, saw initial results from this spacecraft trying to find exactly how the outrageously hot corona propels the solar wind. </p>
<p>Meanwhile, April 8 is a rare opportunity to safely view the sun’s glorious super-heated corona.</p><img src="https://counter.theconversation.com/content/225866/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Martin Connors receives funding from NSERC. </span></em></p>The solar corona can be seen during the solar eclipse on April 8. Astronomers are still trying to figure out the mysteries of the corona, including why it’s so hot.Martin Connors, Professor of Space Science and Physics, Athabasca UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2265582024-03-27T17:07:01Z2024-03-27T17:07:01ZThe total solar eclipse in North America could help shed light on a persistent puzzle about the Sun<figure><img src="https://images.theconversation.com/files/584141/original/file-20240325-24-ot473c.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption"></span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/totality-during-2023-australian-total-solar-2344355767">aeonWAVE / Shutterstock</a></span></figcaption></figure><p>A <a href="https://science.nasa.gov/eclipses/types/#hds-sidebar-nav-1">total solar eclipse</a> takes place on <a href="https://science.nasa.gov/eclipses/future-eclipses/eclipse-2024/">April 8 across North America</a>. These events occur when the Moon passes between the Sun and Earth, completely blocking the Sun’s face. This plunges observers into a darkness similar to dawn or dusk.</p>
<p>During the upcoming eclipse, the path of totality, where observers experience the darkest part of the Moon’s shadow (the umbra), crosses Mexico, arcing north-east through Texas, the Midwest and briefly entering Canada before ending in Maine.</p>
<p>Total solar eclipses occur roughly <a href="https://www.nhm.ac.uk/discover/solar-eclipse-guide.html">every 18 months at some location on Earth</a>. The last total solar eclipse that crossed the US took place on August 21 2017. </p>
<p>An international team of scientists, led by Aberystwyth University, will be conducting experiments from <a href="https://www.fox4news.com/news/2024-eclipse-dallas-crowds-traffic">near Dallas</a>, at a location in the path of totality. The team consists of PhD students and researchers from Aberystwyth University, Nasa Goddard Space Flight Center in Maryland, and Caltech (California Institute of Technology) in Pasadena. </p>
<p>There is valuable science to be done during eclipses that is comparable to or better than what we can achieve via space-based missions. Our experiments may also shed light on a longstanding puzzle about the outermost part of the Sun’s atmosphere – its corona.</p>
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<img alt="Eclipse shadow" src="https://images.theconversation.com/files/584503/original/file-20240326-18-9yqs13.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/584503/original/file-20240326-18-9yqs13.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/584503/original/file-20240326-18-9yqs13.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/584503/original/file-20240326-18-9yqs13.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/584503/original/file-20240326-18-9yqs13.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/584503/original/file-20240326-18-9yqs13.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/584503/original/file-20240326-18-9yqs13.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">The path of eclipse totality passes through Mexico, the US and Canada.</span>
<span class="attribution"><a class="source" href="https://svs.gsfc.nasa.gov/5186/">NASA's Scientific Visualization Studio</a></span>
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<p>The Sun’s intense light is blocked by the Moon during a total solar eclipse. This means that we can observe the <a href="https://solarscience.msfc.nasa.gov/corona.shtml">Sun’s faint corona</a> with incredible clarity, from distances very close to the Sun, out to several solar radii. One radius is the distance equivalent to half the Sun’s diameter, about 696,000km (432,000 miles).</p>
<p>Measuring the corona is extremely difficult without an eclipse. It requires a special telescope <a href="https://www.space.com/what-is-a-coronagraph.html">called a coronagraph</a> that is designed to block out direct light from the Sun. This allows fainter light from the corona to be resolved. The clarity of eclipse measurements surpasses even coronagraphs based in space.</p>
<p>We can also observe the corona on a relatively small budget, compared to, for example, spacecraft missions. A persistent puzzle about the corona is the observation <a href="https://agupubs.onlinelibrary.wiley.com/doi/10.1002/9781119815600.ch2">that it is much hotter</a> than the photosphere (the visible surface of the Sun). As we move away from a hot object, the surrounding temperature should decrease, not increase. How the corona is heated to such high temperatures is one question we will investigate.</p>
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<img alt="Solar eclipse." src="https://images.theconversation.com/files/584507/original/file-20240326-20-xairh2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/584507/original/file-20240326-20-xairh2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=390&fit=crop&dpr=1 600w, https://images.theconversation.com/files/584507/original/file-20240326-20-xairh2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=390&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/584507/original/file-20240326-20-xairh2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=390&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/584507/original/file-20240326-20-xairh2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=490&fit=crop&dpr=1 754w, https://images.theconversation.com/files/584507/original/file-20240326-20-xairh2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=490&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/584507/original/file-20240326-20-xairh2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=490&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-vector/solar-eclipse-diagram-1146598682">Andramin / Shutterstock</a></span>
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<p>We have two main scientific instruments. The first of these is Cip (coronal imaging polarimeter). Cip is also the Welsh word for “glance”, or “quick look”. The instrument takes images of the Sun’s corona with a polariser. </p>
<p>The light we want to measure from the corona is highly polarised, which means it is made up of waves that vibrate in a single geometric plane. A polariser is a filter that lets light with a particular polarisation pass through it, while blocking light with other polarisations. </p>
<p>The Cip images will allow us to measure fundamental properties of the corona, such as its density. It will also shed light on phenomena such as the solar wind. This is a stream of sub-atomic particles in the form of plasma – superheated matter – flowing continuously outward from the Sun. Cip could help us identify sources in the Sun’s atmosphere for certain solar wind streams.</p>
<p>Direct measurements of the magnetic field in the Sun’s atmosphere are difficult. But the eclipse data should allow us to study its fine-scale structure and trace the field’s direction. We’ll be able to see how far magnetic structures called large “closed” magnetic loops extend from the Sun. This in turn will give us information about large-scale magnetic conditions in the corona.</p>
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<img alt="Coronal loops." src="https://images.theconversation.com/files/584489/original/file-20240326-24-zlpsmc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/584489/original/file-20240326-24-zlpsmc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=442&fit=crop&dpr=1 600w, https://images.theconversation.com/files/584489/original/file-20240326-24-zlpsmc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=442&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/584489/original/file-20240326-24-zlpsmc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=442&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/584489/original/file-20240326-24-zlpsmc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=555&fit=crop&dpr=1 754w, https://images.theconversation.com/files/584489/original/file-20240326-24-zlpsmc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=555&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/584489/original/file-20240326-24-zlpsmc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=555&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">Coronal loops are found around sunspots and in active regions of the Sun.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/image-article/coronal-loops-an-active-region-of-sun/">NASA/Solar Dynamics Observatory</a></span>
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<p>The second instrument is Chils (coronal high-resolution line spectrometer). It collects high-resolution spectra, where light is separated into its component colours. Here, we are looking for a particular spectral signature of iron emitted from the corona. </p>
<p>It comprises three spectral lines, where light is emitted or absorbed in a narrow frequency range. These are each generated at a different range of temperatures (in the millions of degrees), so their relative brightness tells us about the coronal temperature in different regions. </p>
<p>Mapping the corona’s temperature informs advanced, computer-based models of its behaviour. These models must include mechanisms for how the coronal plasma is heated to such high temperatures. Such mechanisms might include the conversion of magnetic waves to thermal plasma energy, for example. If we show that some regions are hotter than others, this can be replicated in models. </p>
<p>This year’s eclipse also occurs during a time of heightened solar activity, so we could observe a <a href="https://www.swpc.noaa.gov/phenomena/coronal-mass-ejections">coronal mass ejection (CME)</a>. These are huge clouds of magnetised plasma that are ejected from the Sun’s atmosphere into space. They can affect infrastructure near Earth, causing problems for vital satellites. </p>
<p>Many aspects of CMEs are poorly understood, including their early evolution near the Sun. Spectral information on CMEs will allow us to gain information on their thermodynamics, and their velocity and expansion near the Sun.</p>
<p>Our eclipse instruments have recently been proposed for a space mission called <a href="https://www.surrey.ac.uk/research-projects/feasibility-study-moon-enabled-sun-occultation-mission-mesom">Moon-enabled solar occultation mission (Mesom)</a>. The plan is to orbit the Moon to gain more frequent and extended eclipse observations. It is being planned as a UK Space Agency mission involving several countries, but led by University College London, the University of Surrey and Aberystwyth University.</p>
<p>We will also have an advanced commercial 360-degree camera to collect video of the April 8 eclipse and the observing site. The video is valuable for public outreach events, where we highlight the work we do, and helps to generate public interest in our local star, the Sun.</p><img src="https://counter.theconversation.com/content/226558/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Huw Morgan does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The eclipse will allow scientists to get rare measurements of the Sun’s atmosphere.Huw Morgan, Reader in Physical Sciences, Aberystwyth UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2252412024-03-26T17:25:44Z2024-03-26T17:25:44ZPhotographing the eclipse? You’ll join a long history of people seeking proof of experience<p>If you are <a href="https://www.cbc.ca/news/canada/hamilton/eclipse-day-planning-1.7147091">one of the millions planning to view</a> the total solar eclipse on April 8, there is a good chance that you will take pictures of your experience. </p>
<p>And, like many before you, afterwards you may find that those pictures don’t measure up to your expectations, experiences and memories of viewing the eclipse.</p>
<p>We offer some technical tips for eclipse photography, but we also consider why so many of us are drawn to photograph these kinds of collective moments of awe and wonder — as we think about the larger context of visual culture around solar eclipses throughout history.</p>
<h2>Technical, safety challenges</h2>
<p>Photographing a solar eclipse presents some <a href="https://www.youtube.com/watch?v=dClhdu0oyWM">technical and safety challenges</a>. There are some preparations you can undertake, including ensuring your camera (<a href="https://www.cbc.ca/news/canada/total-solar-eclipse-phone-photos-2024-1.7149062">even smartphone cameras!</a>) has a solar filter. It is also important to be familiar with your camera, to practice using it in different light conditions before the eclipse. </p>
<p>The changes in light qualities will be quick and drastic, so familiarity with aperture and shutter speed will be important on the big day. A tripod will help reduce blurring when a longer exposure is required. If there are clouds, it’s still important to be cautious and wear protective glasses and the ability to capture an image will depend on the extent of cloud cover. The viewing experience will be different, but sky will still darken, creating changes in the colour and the way light passes through the clouds. </p>
<p>There are also some more creative ways to think about capturing the experience, including <a href="https://www.asc-csa.gc.ca/eng/youth-educators/activities/fun-experiments/eclipse-projector.asp">making a pinhole projector</a>. </p>
<p>This simple device can be made from a cardboard box and allows for both safe viewing and some interesting images.</p>
<h2>First photographs of eclipses</h2>
<p>But if your photographs don’t conform to your expectations, you are in good company. In 1842 Italian physicist <a href="https://hyperallergic.com/392269/the-first-photographs-of-a-solar-eclipse/">Gian Alessandro Majocchi attempted to photograph</a> the total solar eclipse that took place that July. Surviving records indicate he only had partial success: His resulting daguerreotype images — an early <a href="https://www.loc.gov/collections/daguerreotypes/articles-and-essays/the-daguerreotype-medium/#">photography technique invented by Louis-Jacques-Mandé Daguerre in 1839, involving treating a silver-coated copper plate with light sensitive chemicals</a> — are lost.</p>
<p>Majocchi was able to capture a few photographs <a href="https://babel.hathitrust.org/cgi/pt?id=hvd.fl1241&view=1up&seq=265">before and after</a> the <a href="https://www.cbc.ca/news/science/total-solar-eclipse-where-how-1.7129716">moments of totality</a>.</p>
<h2>Reminder of wonder, togetherness</h2>
<p>Apart from technical aspects, a successful photograph of the eclipse serves as a lasting reminder of the sense of wonder and the feeling of being part of something larger than ourselves. </p>
<p>This is the kind of event that brings people together, and the shared experience continues long after the eclipse ends through photographs that serve as memory markers and tangible proof that you were there to witness the eclipse. And even though many of us might end up with similar photographs, there is something significant about so many people taking pictures of the same event.</p>
<p>For example, <a href="https://psycnet.apa.org/record/2016-27715-001">taking photographs of events can increase a person’s enjoyment of the experience</a>, as the research of marketing professor Kristin Diehl and colleagues has examined. </p>
<p>Photography allows us to preserve memories, share them with others and relive those moments in the future. What makes an image stand out among the millions shared daily on social media often comes down to a combination of factors: its visual impact, the story it tells and the emotional resonance it can hold for others viewing it. In other words, much of what we share is about the broader experience.</p>
<h2>Proof of experience, connection across time</h2>
<p>Photographs also have long fulfilled a deep-seated need for proof of experience. We were there. Whether a blurry cell phone image of the <em>Mona Lisa</em> or a snapshot of the eclipse, these images serve as tangible reminders of our experiences. They validate our memories, anchor the stories we tell and allow us to share these moments with others. </p>
<p>Looking at images of people taking in <a href="https://www.atlasobscura.com/articles/century-eclipse-watching-photos">an eclipse during other eras can also offer a shared sense of connection across time</a>. This is a phenomenon that is bigger than us and these images connect us to the experiences of previous generations. </p>
<p>Scientific photographs of an eclipse, like the ones <a href="https://siarchives.si.edu/collections/siris_arc_308088">Thomas Smillie</a> made for the Smithsonian in 1900, may have been heralded as <a href="https://siarchives.si.edu/blog/smillie-and-1900-eclipse">technological breakthroughs</a>. Yet <a href="https://www.atlasobscura.com/articles/century-eclipse-watching-photos">there is something especially compelling about photographs of people gathered together, stopping for a moment and looking skyward</a>.</p>
<h2>Photographs yield partial insights</h2>
<p>A <a href="https://hyperallergic.com/392269/the-first-photographs-of-a-solar-eclipse/">daguerreotype of a solar eclipse taken on July 28, 1851 is the first known successful photograph of the solar corona</a>. This image was made at the Royal Prussian Observatory in Königsberg (contemporary Kaliningrad, Russia) by Johann Julius Friedrich Berkowski with the aid of a telescope. <a href="https://www.space.com/37656-first-total-solar-eclipse-photo-ever.html">The 84-second exposure allowed Berkowski to capture the moment in incredible detail</a>.</p>
<p>In 1890, the <em>American Journal of Photography</em> proclaimed <a href="https://babel.hathitrust.org/cgi/pt?id=hvd.fl1241&view=1up&seq=265">“probably in no department of science, certainly in no branch of astronomical science, has photography been of such use as in the study of solar eclipses</a>.” As the editors note, photography certainly can shape our understanding of the world, help to create new knowledge and provide valuable insights into the nature of the universe. </p>
<p>But there is also a limit to what photography can do. The experience of a solar eclipse goes beyond the visible: <a href="https://eclipse2017.nasa.gov/temperature-change-during-totality">temperatures drop</a>, <a href="https://www.audubon.org/news/total-solar-eclipse-coming-how-will-birds-and-other-wildlife-react">the behaviour of nonhuman animals can suddenly shift</a> and many report <a href="https://www.cbc.ca/player/play/1.7149511">unanticipated emotional or spiritual responses</a>.</p>
<h2>Many visual, artistic responses</h2>
<p>Further, there is a long history of <a href="https://doi.org/10.1038/508314a">eclipses being recorded in a range of different visual media</a>. For example, the <a href="https://doi.org/10.1017/S1743921314004621">Shang Dynasty in China provides a visual record of solar eclipses</a> via ancient script carved <a href="https://asia-archive.si.edu/learn/chinas-calligraphic-arts/oracle-bone-script">into oracle bones</a>.</p>
<p><a href="https://smarthistory.org/peter-paul-rubens-elevation-of-the-cross/">A 1610 painting by Peter Paul Rubens, called <em>The Elevation of the Cross</em></a>, illustrates the long and complex history of connections between phenomenon like eclipses and religious beliefs. In the early 20th century, American painter Howard Russell Butler produced a series of paintings in which he focused on <a href="https://hyperallergic.com/393623/howard-russell-butler-eclipse-paintings/">aspects of the eclipse that were difficult to capture with black and white photography — the changing quality of light and colours of the sky</a>. </p>
<p>The <a href="https://artmuseum.princeton.edu/transient-effects/eclipses-art/blackstar">video accompanying David Bowie’s <em>Black Star</em></a> (2016) opens with a total solar eclipse.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/kszLwBaC4Sw?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Video for David Bowie’s ‘Black Star.’</span></figcaption>
</figure>
<p>This is evocative visual imagery that complements the song’s themes of mortality — and offers a nod to long-held understandings of an eclipse as a symbol of impending doom. This symbolism was especially poignant as this was the title track of Bowie’s last studio album.</p>
<p>These types of artistic responses to celestial events foreground personal interpretation and emotional responses. They also foreground and reflect social, cultural, and spiritual meanings associated with a solar eclipse. </p>
<p>Could the act of sharing our eclipse photographs provide a point of fusion between providing evidence and these less tangible — but equally valid — moments of engagement?</p><img src="https://counter.theconversation.com/content/225241/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Keri Cronin has previously received funding from the Social Sciences and Humanities Research Council of Canada.</span></em></p><p class="fine-print"><em><span>Amy Friend does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Apart from technical aspects, a successful photograph of the eclipse serves as a lasting reminder of the sense of wonder and the feeling of being part of something larger than ourselves.Amy Friend, Associate professor, Visual Arts Department, Brock UniversityKeri Cronin, Professor, History of Art & Visual Culture, Brock UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2242982024-03-26T12:48:20Z2024-03-26T12:48:20Z3 ways to use the solar eclipse to brighten your child’s knowledge of science<figure><img src="https://images.theconversation.com/files/583531/original/file-20240321-16-fk38cj.jpg?ixlib=rb-1.1.0&rect=0%2C60%2C6720%2C4406&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">In no case should a child look directly at the solar eclipse, but there are special eclipse glasses.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/child-observes-the-annular-solar-eclipse-by-using-special-news-photo/1724609614?adppopup=true">Anadolu via Getty Images</a></span></figcaption></figure><p>When the Moon passes between the Sun and the Earth on April 8, 2024, it will represent a rare astronomical event that won’t take place for <a href="https://science.nasa.gov/eclipses/future-eclipses/eclipse-2024/">another 20 years</a> – a <a href="https://science.nasa.gov/eclipses/future-eclipses/eclipse-2024/where-when/">total solar eclipse</a>. For parents and educators, at least those who live along an arc of land from Texas up through Indiana and Maine, it offers a unique and memorable learning opportunity. </p>
<p>As STEM researchers at <a href="https://hhs.purdue.edu/center-for-early-learning/">Purdue’s Center for Early Learning</a>, we suggest three ways to make the total solar eclipse a fun experience for young children and <a href="https://doi.org/10.1080/15248372.2019.1620232">teach some important science</a> along the way.</p>
<h2>1. Discuss historical versus modern understandings of eclipses</h2>
<p>It is important that children learn to <a href="https://www.sciencepracticesleadership.com/uploads/1/6/8/7/1687518/reiser,_berland,_&_kenyon_(2012).pdf">consider and contrast multiple ideas</a> when developing explanations for why something happens. One way to do this is to compare historical and modern explanations for why solar eclipses occur. </p>
<p>Share with the kids that, historically, many people across cultures feared eclipses. Some thought they <a href="https://www.britannica.com/list/the-sun-was-eaten-6-ways-cultures-have-explained-eclipses">signified disapproval from the gods</a>. Others believed they predicted bad tidings to come, including <a href="https://www.folger.edu/blogs/collation/black-monday-great-solar-eclipse-1652/">shipwrecks and storms</a>.</p>
<p>Contrast those explanations with easy-to-understand scientific explanations of today. Britannica Kids offers a great <a href="https://kids.britannica.com/kids/article/eclipse/353079">resource for children under 8</a>. Scientific American has a webpage that <a href="https://www.scientificamerican.com/article/how-to-explain-aprils-total-solar-eclipse-to-kids/">works well for older kids</a>. </p>
<p>When contrasting scientific evidence with historical beliefs, it is important not to be critical of other cultures. Use the eclipse to talk about how scientific knowledge is built over time through observation. There are many things we do not know now that we will learn 10, 20 or even 100 years from now. </p>
<h2>2. Have conversations using scientific language</h2>
<p>Teaching children about the solar eclipse isn’t just about explaining the what and the why. It’s also about engaging in rich dialogue. Our prior research shows that young children’s science knowledge is <a href="https://doi.org/10.1016/j.cogdev.2020.100981">highly based on language</a>. Both <a href="https://doi.org/10.1016/j.jecp.2022.105473">parents</a> and <a href="https://doi.org/10.1080/10409289.2010.507496">teachers</a> play a role in shaping this language. </p>
<p>Use science-related vocabulary to enrich children’s understanding of the eclipse. Examples include: orbit, rotate, spin, reemerge, Sun, Moon, Earth, far, distance, total and partial. </p>
<p><a href="https://doi.org/10.1080/07370008.2011.608027">Children understand science concepts more deeply</a> and <a href="https://doi.org/10.1002/trtr.2075">use more complex vocabulary</a> when adults use inquiry-based strategies. For example, adults can ask children what they see happening while watching the eclipse and why they think that is. Then the adults can ask the children to make predictions about what else could happen and provide evidence for their explanations. </p>
<p>Children can document their observations throughout the eclipse in their own <a href="https://doi.org/10.1016/j.ecresq.2004.01.009">science journals</a> using both science-related vocabulary and drawings of what they see. The journals are a great opportunity to discuss their ideas and have rich conversations.</p>
<h2>3. Use household items to help children understand the eclipse</h2>
<p>Three-dimensional models allow children to visualize things that are otherwise difficult to see, such as the orbit of the Earth and the Moon. Comparisons between the model and their observations of real life, especially when guided by a teacher or parent, <a href="https://doi.org/10.1177/0956797619864601">help children build knowledge</a> about complex topics in science.</p>
<p>During the solar eclipse, the Moon moves directly between the Earth and the Sun. In small groups at school or at home, one child can represent the Earth, while another holds a basketball to represent the Sun and another a tennis ball to represent the Moon.</p>
<p>The child representing the Earth can orbit the Sun and rotate in place, experimenting with changing their distance from the Sun and Moon. Closing one eye, the child may eventually see the basketball completely blocked by the tennis ball when it aligns just right. This is what happens in a total solar eclipse. </p>
<p>In this exercise, children are not only modeling the eclipse but also building scientific vocabulary. Throughout the activity, parents and teachers can ask children to compare and contrast the model to their own observations. They can ask questions, such as why do the Sun and Moon look like they are similar sizes in the sky, even though we know that the Sun is many times larger than the Moon? If the Moon is smaller, how does it block the Sun completely? The key is to help children generate hypotheses, test their ideas and then develop new conclusions.</p>
<p>We hope these ideas will encourage everyone to take advantage of this wonderful scientific learning experience. We also warn you not to look directly into the Sun during the eclipse and to get the right <a href="https://eclipse.aas.org/eye-safety/viewers-filters">eclipse glasses</a>. Looking directly at the Sun, even through sunglasses or cameras, <a href="https://theconversation.com/total-solar-eclipses-while-stunning-can-damage-your-eyes-if-viewed-without-the-right-protection-221381">can cause severe injury to the eyes</a>.</p><img src="https://counter.theconversation.com/content/224298/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>If you have young kids, the solar eclipse on April 8, 2024, represents a rare opportunity to teach them about science.David J. Purpura, Professor of Human Development and Family Science; Director of the Center for Early Learning, Purdue UniversityLauren Westerberg, Doctoral Candidate in Human Development and Family Science, Purdue UniversitySona Kumar, Postdoctoral Researcher in the Department of Human Development and Family Science, Purdue UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2259552024-03-22T12:32:20Z2024-03-22T12:32:20ZAn eclipse for everyone – how visually impaired students can ‘get a feel for’ eclipses<figure><img src="https://images.theconversation.com/files/583493/original/file-20240321-24-k7j1j4.jpg?ixlib=rb-1.1.0&rect=0%2C5%2C1997%2C1398&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A solar eclipse approaching totality. </span> <span class="attribution"><a class="source" href="https://newsroom.ap.org/detail/Total%20Solar%20Eclipse%20Photo%20Gallery/d4f2edfa2e47448980ce303f299063ae?hpSectionId=8053d9e3a7de4b25a8bccd33428f5964&st=hpsection&mediaType=photo&sortBy=arrivaldatetime:desc&dateRange=Anytime&totalCount=3429&currentItemNo=22">AP Photo/Richard Vogel, File</a></span></figcaption></figure><p>Many people in the U.S. will have an opportunity to witness nearly four minutes of a <a href="https://theconversation.com/what-would-a-solar-eclipse-look-like-from-the-moon-an-astronomer-answers-that-and-other-total-eclipse-questions-81308">total solar eclipse</a> on Monday, April 8, 2024, as it moves from southern Texas to Maine. But in the U.S., over 7 million people are <a href="https://nfb.org/blindness-statistics">blind or visually impaired</a> and may not be able to experience an eclipse the traditional way. </p>
<p>Of course they, like those with sight, will feel colder as the Sun’s light is shaded, and will hear the songs and sounds of birds and insects change as the light dims and brightens. But much of an eclipse is visual.</p>
<p>We are a <a href="https://scnasaepscor.charleston.edu/contact-us/">planetary scientist</a> and <a href="https://www.edinboro.edu/academics/schools-and-departments/cshp/departments/geosciences/planetarium/director.php">an astronomer</a> who, with funding and support from NASA’s <a href="https://sservi.nasa.gov/articles/">Solar System Exploration Research Virtual Institute</a>, have created and published a set of <a href="https://sservi.nasa.gov/books/eclipses.html">tactile graphics</a>, or graphics with raised and textured elements, on the 2024 total solar eclipse. </p>
<p>The guide, called “Getting a Feel for Eclipses,” illustrates the paths of the 2017 total, 2023 annular and <a href="https://science.nasa.gov/eclipses/future-eclipses/eclipse-2024/where-when/">2024 total solar eclipses</a>. In a <a href="https://theconversation.com/what-would-a-solar-eclipse-look-like-from-the-moon-an-astronomer-answers-that-and-other-total-eclipse-questions-81308">total eclipse</a>, the Moon fully blocks the Sun from Earth view, while during an <a href="https://www.nesdis.noaa.gov/annular-solar-eclipse">annular eclipse</a>, a narrow ring of sunlight can be seen encircling the Moon. </p>
<p>The tactile graphics and associated online content detail the <a href="https://theconversation.com/solar-eclipses-result-from-a-fantastic-celestial-coincidence-of-scale-and-distance-224113">specific alignment of the Earth, Moon and Sun</a> under which eclipses occur. </p>
<p>To date, we have distributed almost 11,000 copies of this book to schools for the blind, state and local libraries, the Library of Congress and more.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/583257/original/file-20240320-20-10b7nu.jpg?ixlib=rb-1.1.0&rect=25%2C3%2C2085%2C1553&q=45&auto=format&w=1000&fit=clip"><img alt="A map of the US with three curved lines stretching across, indicating the eclipses of 2024, 2023 and 2017." src="https://images.theconversation.com/files/583257/original/file-20240320-20-10b7nu.jpg?ixlib=rb-1.1.0&rect=25%2C3%2C2085%2C1553&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/583257/original/file-20240320-20-10b7nu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=443&fit=crop&dpr=1 600w, https://images.theconversation.com/files/583257/original/file-20240320-20-10b7nu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=443&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/583257/original/file-20240320-20-10b7nu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=443&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/583257/original/file-20240320-20-10b7nu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=556&fit=crop&dpr=1 754w, https://images.theconversation.com/files/583257/original/file-20240320-20-10b7nu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=556&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/583257/original/file-20240320-20-10b7nu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=556&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">‘The Getting A Feel for Eclipses’ guide helps blind and visually impaired people learn about the eclipse.</span>
<span class="attribution"><a class="source" href="https://sservi.nasa.gov/books/eclipses.html">NASA SSERVI</a></span>
</figcaption>
</figure>
<h2>Why publish a tactile book on eclipses?</h2>
<p>NASA has <a href="https://science.nasa.gov/eclipses">lots of explanatory material</a> that helps people visualize and understand rare phenomena like eclipses. But for people with visual impairments, maps and images don’t help. For tactile readers, their sense of touch is their vision. That’s where this guide and our other tactile books come in.</p>
<p>Over <a href="https://nfb.org/blindness-statistics">65,000 students in the U.S.</a> are blind or visually impaired. After working with several of our students who are totally blind, we wanted to find out how to make events like eclipses as powerful for these students as they are for us. We also wanted to help our students visualize and understand the concept of an eclipse. </p>
<p>These aims resulted in the three <a href="https://www.pathstoliteracy.org/tactile-graphics/">tactile graphics</a>, which are physical sheets with textures and raised surfaces that can be interpreted through touch, <a href="https://sservi.nasa.gov/books/eclipses.html">as well as online content</a>. </p>
<p>The first tactile graphic models the <a href="https://theconversation.com/solar-eclipses-result-from-a-fantastic-celestial-coincidence-of-scale-and-distance-224113">alignment of the Earth, Moon and Sun</a>. The second illustrates the phases of an eclipse as the Moon moves in between the Earth and Sun to full totality, and then out of the way. The third includes a map of the continental U.S. that illustrates the paths of three eclipses: the <a href="https://www.weather.gov/pah/TotalSolarEclipse2017">Aug. 21, 2017, total eclipse</a>, the <a href="https://science.nasa.gov/eclipses/future-eclipses/eclipse-2023/where-when/">Oct. 14, 2023, annular eclipse</a> and the <a href="https://science.nasa.gov/eclipses/future-eclipses/eclipse-2024/where-when/">Apr. 8, 2024, total eclipse</a>. We used different textures to illustrate these concepts.</p>
<p>Each book includes a QR code on the front cover, outlined by a raised square boundary. The code links to <a href="https://sservi.nasa.gov/books/eclipses.html">an online guide</a> that leads the user through the content behind the graphics while also providing background information. With the online content, users may opt to print the information in large font or have it read to them by a device.</p>
<p>Although initially created to assist visually impaired audiences, these books are still helpful resources for those with sight. Some students can see but might learn better when able to explore the tactile parts of the guide while listening to the audio. Often it’s helpful for students to get the same information presented in different styles, with options to read or have the content information read to them. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/583490/original/file-20240321-18-camylh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A sheet of paper with raised textures labeled Sun, Umbra, Moon and Totality, with three students touching the textures." src="https://images.theconversation.com/files/583490/original/file-20240321-18-camylh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/583490/original/file-20240321-18-camylh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/583490/original/file-20240321-18-camylh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/583490/original/file-20240321-18-camylh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/583490/original/file-20240321-18-camylh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/583490/original/file-20240321-18-camylh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/583490/original/file-20240321-18-camylh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Students at Florida School for the Deaf and Blind in St. Augustine explore tactiles 1 and 2.</span>
<span class="attribution"><span class="source">Florida School for the Deaf and Blind</span></span>
</figcaption>
</figure>
<h2>How are the books made?</h2>
<p>We hand-make each book starting by identifying which science concepts the user will likely want to know, and which illustrations can support those concepts.</p>
<p>Once identified, the next step is to create a tactile master, or model, which has one or more raised textures that help to define the science concepts. We pick a set of unique textures to use on the master to signify different items, so the Sun feels different than the Earth. This way, the textures of the graphics become part of the story being shared. </p>
<p>For example, in a model of the Sun’s surface, we use <a href="https://www.britannica.com/plant/Spanish-moss">Spanish moss</a> to create the dynamic texture of the Sun. In past projects, we’ve used textures like doll hair, sand and differently textured cardboard to illustrate planet features, instruments on spacecraft, fine surface features and more. Then, we add <a href="https://www.afb.org/blindness-and-low-vision/braille/what-braille">Braille labels</a> for figure titles, key features and specific notes.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/583492/original/file-20240321-28-ku4w3n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A circle filled with moss." src="https://images.theconversation.com/files/583492/original/file-20240321-28-ku4w3n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/583492/original/file-20240321-28-ku4w3n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=800&fit=crop&dpr=1 600w, https://images.theconversation.com/files/583492/original/file-20240321-28-ku4w3n.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=800&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/583492/original/file-20240321-28-ku4w3n.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=800&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/583492/original/file-20240321-28-ku4w3n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1005&fit=crop&dpr=1 754w, https://images.theconversation.com/files/583492/original/file-20240321-28-ku4w3n.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1005&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/583492/original/file-20240321-28-ku4w3n.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1005&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The tactile master – Spanish moss – used for the Sun.</span>
<span class="attribution"><span class="source">Cassandra Runyon</span></span>
</figcaption>
</figure>
<p>Once we’ve finished making the masters and laying out each page, a small family print shop – McCarty Printing in Erie, Pennsylvania – prints the page titles and key feature labels on Brailon, a type of plastic paper. </p>
<p>Once printed, we place the masters and the Brailon sheets on a thermoform Machine, which heats up the sheets and creates a vacuum that forms the final tactile graphics. Then, we return the pages to McCarty Printing for binding. </p>
<h2>Viewing and experiencing the eclipse</h2>
<p>Like fully sighted people, people with partial vision should avoid looking directly at the Sun. Instead, everyone should <a href="https://theconversation.com/total-solar-eclipses-while-stunning-can-damage-your-eyes-if-viewed-without-the-right-protection-221381">use eclipse glasses</a>. If you don’t have eclipse glasses, you can use an indirect viewing method such as a <a href="https://science.nasa.gov/eclipses/future-eclipses/eclipse-2024/safety/">colander or pinhole projector</a>.</p>
<p>As the eclipse approaches totality, take time to enjoy your surroundings, feel the changes in temperature and light, and note how the animals around you react to the remarkable event using another of your senses – sound.</p><img src="https://counter.theconversation.com/content/225955/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Cassandra Runyon receives funding from NASA's Office of STEM Engagment through the National Space Grant Program and the Established Program to Stimulate Competitive Research (EPSCoR) as well as NASA's Solar System Exploration Research Virtual Institure (SSERVI). She is the Director of both the NASA South Carolina Space Grant Consortium and NASA South Carolina EPSCoR program and Vice Chair of the National Council of Space Grant Directors.</span></em></p><p class="fine-print"><em><span>David Hurd receives funding from the NSF and NASA SSERVI.</span></em></p>Eclipses are rare, fantastic celestial events. Here’s how educators can help visually impaired students enjoy eclipses alongside their sighted peers.Cassandra Runyon, Professor of Geology & Environmental Geosciences, College of CharlestonDavid Hurd, Professor of Geosciences, Pennsylvania Western UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2227072024-03-13T19:13:22Z2024-03-13T19:13:22ZTotal solar eclipses provide an opportunity to engage with science, culture and history<figure><img src="https://images.theconversation.com/files/580943/original/file-20240311-16-li8vda.jpg?ixlib=rb-1.1.0&rect=0%2C5%2C3724%2C2146&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Throughout time, eclipses have inspired societies to understand the cosmos and its events.</span> <span class="attribution"><span class="source">(Shutterstock)</span></span></figcaption></figure><p>On April 8, 2024, there will be a total solar eclipse in Canada. This is an opportunity to experience, learn from and participate in the excitement and wonder. And rather than hiding inside, researchers have been communicating how people can safely enjoy this unique opportunity.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/on-april-8-2024-parts-of-ontario-quebec-the-maritimes-and-newfoundland-will-see-a-total-eclipse-of-the-sun-heres-how-to-get-ready-for-it-203382">On April 8, 2024, parts of Ontario, Québec, the Maritimes and Newfoundland will see a total eclipse of the sun. Here's how to get ready for it.</a>
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<p>Roughly every 18 months, the sun, moon and Earth come into perfect alignment and somewhere on Earth <a href="https://eclipse.gsfc.nasa.gov/SEatlas/SEatlas.html">experiences a solar eclipse</a>. During this phenomenon, the moon casts a roughly 250 km wide shadow onto Earth.</p>
<p>This ephemeral daytime darkness can be a once-in-a-lifetime experience. The last time Toronto experienced a total solar eclipse was on <a href="http://xjubier.free.fr/en/site_pages/solar_eclipses/xSE_GoogleMap3.php?Ecl=+19250124&Acc=2&Umb=1&Lmt=1&Mag=0&Lat=43.69660&Lng=-79.41391&Elv=162.0&Zoom=8&LC=1">Jan. 24, 1925</a>; the next total solar eclipse will occur in 120 years, on <a href="http://xjubier.free.fr/en/site_pages/solar_eclipses/xSE_GoogleMap3.php?Ecl=+21441026&Acc=2&Umb=1&Lmt=1&Mag=0&Lat=43.69629&Lng=-79.29982&Elv=127.0&Zoom=8&LC=1">Oct. 26, 2144</a>.</p>
<p>Our interpretation of, and response to, total solar eclipses has advanced enormously. Eclipses were once considered cosmic omens that predicted dying kings, good harvests or the need for new territorial treaties. Today, they provide a unique opportunity to consider the physical nature of the universe, and the cosmic privilege of witnessing the alignment of the moon and sun. </p>
<h2>Eclipses and knowledge creation</h2>
<p>Due to their sudden darkness, solar eclipses have been perceived <a href="https://www.cnn.com/2017/07/25/us/history-solar-eclipse/index.html">through history as catastrophic events</a>. Many societies developed stories to <a href="https://www.britannica.com/list/the-sun-was-eaten-6-ways-cultures-have-explained-eclipses">explain these unusual events</a>, often filled with fear and violence. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/580949/original/file-20240311-26-98odlu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="an illustration of a golden brown demon eating a yellow disc against a purple background" src="https://images.theconversation.com/files/580949/original/file-20240311-26-98odlu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/580949/original/file-20240311-26-98odlu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=451&fit=crop&dpr=1 600w, https://images.theconversation.com/files/580949/original/file-20240311-26-98odlu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=451&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/580949/original/file-20240311-26-98odlu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=451&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/580949/original/file-20240311-26-98odlu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=567&fit=crop&dpr=1 754w, https://images.theconversation.com/files/580949/original/file-20240311-26-98odlu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=567&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/580949/original/file-20240311-26-98odlu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=567&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A mural of the Hindu demon Rahu swallowing the moon at the temple Wat Phang La in southern Thailand.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/anandajoti/10684670235/">(Anandajoti Bhikkhu/flickr)</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Indian myths tell of an <a href="https://www.washingtonpost.com/graphics/2017/lifestyle/eclipse-myths/">immortal demon seeking revenge on Vishnu by trying to eat the sun and moon</a>. The Pomo, Indigenous people of Northern California, describe <a href="https://www.exploratorium.edu/eclipse/eclipse-stories-from-around-the-world">a huge angry bear trying to eat the sun</a>. In other mythologies, eclipses were thought to be heavenly forces removing our source of warmth and life.</p>
<p>Beliefs about eclipses motivated ancient Greek astronomers to create the <a href="https://doi.org/10.1371/journal.pone.0103275">antikythera mechanism</a>, a complex analog computer that predicted the timing of future eclipses with a precision of 30 minutes. These predictions were critical for Greek society as a solar eclipse could mean an upcoming death of the king, requiring the appointment of a pseudo-emperor to be killed instead.</p>
<p>Our reactions to eclipses have evolved, driving us to better understand the solar system and the universe at large. </p>
<p>During the eclipse on Aug. 18, 1868, astronomers Norman Lockyer and Pierre Janssen each studied the light from the solar corona to <a href="https://doi.org/10.1007/978-1-4614-5363-5">discover a new chemical element</a>. This chemical element was named helium, after the Greek word for the sun. </p>
<p>On May 29, 1919, Frank Watson Dyson and Arthur Stanley Eddington studied the <a href="https://doi.org/10.1098/rsta.1920.0009">bent path of starlight</a> during a total solar eclipse for the first experimental “<a href="https://timesmachine.nytimes.com/timesmachine/1919/11/10/118180487.pdf">triumph of Einstein’s theory</a>” of general relativity.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/580945/original/file-20240311-20-25sylo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="ancient greenish square fragments" src="https://images.theconversation.com/files/580945/original/file-20240311-20-25sylo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/580945/original/file-20240311-20-25sylo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/580945/original/file-20240311-20-25sylo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/580945/original/file-20240311-20-25sylo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/580945/original/file-20240311-20-25sylo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/580945/original/file-20240311-20-25sylo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/580945/original/file-20240311-20-25sylo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Fragments of an antikythera mechanism on display at a museum in Athens, Greece.</span>
<span class="attribution"><span class="source">(Shutterstock)</span></span>
</figcaption>
</figure>
<h2>Eclipse experiences</h2>
<p>Unlike many other cosmic events, such as meteor showers or comets, which require expensive telescopes or <a href="https://darksky.org/what-we-do/international-dark-sky-places/">dark sky places</a>, eclipses are a barrier-free celestial event. To safely enjoy the eclipse, one simply needs eclipse viewing glasses or <a href="https://www.jpl.nasa.gov/edu/learn/project/how-to-make-a-pinhole-camera/">a cardboard box</a>. </p>
<p>Many universities across Canada are using the opportunity of the total solar eclipse to engage with people to safely experience this astronomical phenomenon. For example, Queen’s University in Kingston, Canada is making <a href="https://www.queensu.ca/physics/2024-total-solar-eclipse/eclipse-glasses">120,000 eclipse glasses available</a> to make safe eclipse viewing possible for anyone.</p>
<p>In the spirit of education, hundreds of <a href="https://astrosociety.org/education-outreach/amateur-astronomers/eclipse-ambassadors/program.html">eclipse ambassadors</a> are heading to schools to engage with students about having a profound and safe experience during the eclipse. These ambassadors lead workshops on building inexpensive pinhole cameras to project the sun during the eclipse, explaining unique features that can be seen during eclipses, such as <a href="https://science.nasa.gov/resource/baileys-beads/">Bailey’s beads</a> and the <a href="https://www.nasa.gov/image-article/diamond-ring-effect/">diamond ring effect</a>, and helping everyone appreciate the vastness of the solar system.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/580952/original/file-20240311-20-8t2snr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="a black circle surrounded with a ring of light that is thicker in the lower righthand quadrant" src="https://images.theconversation.com/files/580952/original/file-20240311-20-8t2snr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/580952/original/file-20240311-20-8t2snr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=389&fit=crop&dpr=1 600w, https://images.theconversation.com/files/580952/original/file-20240311-20-8t2snr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=389&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/580952/original/file-20240311-20-8t2snr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=389&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/580952/original/file-20240311-20-8t2snr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=489&fit=crop&dpr=1 754w, https://images.theconversation.com/files/580952/original/file-20240311-20-8t2snr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=489&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/580952/original/file-20240311-20-8t2snr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=489&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The Baily’s Beads effect occurs when gaps in the moon’s rugged terrain allow sunlight to pass through in some places just before the total phase of the eclipse.</span>
<span class="attribution"><a class="source" href="https://science.nasa.gov/resource/baileys-beads/">(Aubrey Gemignani/NASA)</a></span>
</figcaption>
</figure>
<p>These efforts demonstrate the universal value of science, and promote science engagement beyond classrooms and institutions.</p>
<p>Not only is the upcoming eclipse being leveraged as an opportunity to inspire the next generation of scientists, but it is also being used for the advancement of scientific knowledge. Unlike the experiments of Dyson, Eddington and Lockyer that were limited to the academy, today’s institutions are mobilizing the public to conduct citizen science experiments. </p>
<p>Initiated by NASA, the <a href="https://eclipsemegamovie.org/goals">Eclipse Megamovie project</a> will use photos taken during totality of the solar eclipse to study the solar corona. In 2017, photos collected during the total eclipse helped researchers identify a plasma plume in the solar corona. The 2024 eclipse will help researchers study this plume in greater detail. </p>
<p>Anyone with a DSLR camera and a tripod can submit a picture of the total solar eclipse to the Eclipse Megamovie project. The public data collected for the 2024 eclipse will far exceed what could be accomplished by any one experiment or location.</p>
<p>April’s total solar eclipse, and others to come, will remind people that science is exciting and inspiring, and that scientific expertise is of profound universal value. Such a celestial coincidence is an opportunity to engage with local communities and discuss the origin and mechanics of our solar system, all while including the public in scientific discovery through crowd-sourcing images of their experience. </p>
<p>All that’s left is to hope for clear skies and marvel once more at the cosmos.</p><img src="https://counter.theconversation.com/content/222707/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Nikhil Arora receives funding from the National Sciences and Engineering Research Council of Canada.</span></em></p><p class="fine-print"><em><span>Mark Richardson is based at the Arthur B. McDonald Canadian Astroparticle Physics Research Institute, who has received funding from the Canada First Research Excellence Fund. </span></em></p>Eclipses have inspired myths, predictions and scientific discoveries. The total solar eclipse occurring on April 8 provides a once-in-a-lifetime opportunity to engage with science and the cosmos.Nikhil Arora, Postdoctoral fellow, Physics, Engineering Physics & Astronomy, Queen's University, OntarioMark Richardson, Manager for Education and Public Outreach, Adjunct Professor of Physics and Astronomy, Queen's University, OntarioLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2241132024-03-12T18:55:13Z2024-03-12T18:55:13ZSolar eclipses result from a fantastic celestial coincidence of scale and distance<figure><img src="https://images.theconversation.com/files/580531/original/file-20240307-28-al4bnq.jpg?ixlib=rb-1.1.0&rect=23%2C15%2C5247%2C3690&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Solar eclipses happen because of a few factors, including the Moon's size and distance from the Sun. </span> <span class="attribution"><a class="source" href="https://newsroom.ap.org/detail/EclipseKentucky/8b202fc6981149ebb1c59158d49e348d/photo?Query=eclipse&mediaType=photo&sortBy=&dateRange=Anytime&totalCount=478&digitizationType=Digitized&currentItemNo=7&vs=true&vs=true">AP Photo/Timothy D. Easley</a></span></figcaption></figure><p>On April 8, 2024, millions across the U.S. will have the once-in-a-lifetime chance to view a total solar eclipse. <a href="https://science.nasa.gov/eclipses/future-eclipses/eclipse-2024/where-when/">Cities including</a> Austin, Texas; Buffalo, New York; and Cleveland, Ohio, will have a direct view of this rare cosmic event that lasts for just a few hours.</p>
<p>While <a href="https://theconversation.com/astro-tourism-chasing-eclipses-meteor-showers-and-elusive-dark-skies-from-earth-207969">you can see many astronomical events</a>, such as <a href="https://theconversation.com/comets-101-everything-you-need-to-know-about-the-snow-cones-of-space-213342">comets</a> and meteor showers, from anywhere on Earth, eclipses are different. You need to travel to what’s called the <a href="https://theconversation.com/when-the-sun-goes-dark-5-questions-answered-about-the-solar-eclipse-81308">path of totality</a> to experience the full eclipse. Only certain places get an eclipse’s full show, and that’s because of scale. </p>
<p>The relatively small <a href="https://www.space.com/18135-how-big-is-the-moon.html">size of the Moon</a> and its shadow make eclipses truly once-in-a-lifetime opportunities. On average, total solar eclipses are visible somewhere on Earth once every few years. But from any one location on Earth, <a href="https://eclipse.gsfc.nasa.gov/SEcirc/SEcirc.html">it is roughly 375 years</a> between solar eclipses.</p>
<p><a href="https://science.psu.edu/astro/people/cxp137">I’m an astronomer</a>, but I have never seen a total solar eclipse, so I plan to drive to Erie, Pennsylvania, in the path of totality, for this one. This is one of the <a href="https://eclipse.gsfc.nasa.gov/SEmap/SEmapNA/TSENorAm2051.gif">few chances I have</a> to see a total eclipse without making a much more expensive <a href="https://theconversation.com/astro-tourism-chasing-eclipses-meteor-showers-and-elusive-dark-skies-from-earth-207969">trip to someplace more remote</a>. Many people have asked me why nearby eclipses are so rare, and the answer is related to the size of the Moon and its distance from the Sun.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/fmtGqOxxmEU?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Those in the path of totality will have the opportunity to see a total solar eclipse this April.</span></figcaption>
</figure>
<h2>Size and scale</h2>
<p>You can observe a solar eclipse when the Moon passes in front of the Sun, blocking some or all of the Sun from view. For people on Earth to be able to see an eclipse, the Moon, while orbiting around the Earth, must lie exactly along the observer’s line of sight with the Sun. Only some observers will see an eclipse, though, because not everyone’s view of the Sun will be blocked by the Moon on the day of an eclipse. </p>
<p>The fact that solar eclipses happen at all is a bit of a numerical coincidence. It just so happens <a href="https://science.nasa.gov/sun/facts/#hds-sidebar-nav-3">that the Sun</a> is approximately 400 times <a href="https://science.nasa.gov/moon/facts/#hds-sidebar-nav-3">larger than the Moon</a> and also 400 times more distant from the Earth. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/581049/original/file-20240311-22-9ovtoi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A photo showing the Earth next to the Moon. The Earth is much larger." src="https://images.theconversation.com/files/581049/original/file-20240311-22-9ovtoi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/581049/original/file-20240311-22-9ovtoi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/581049/original/file-20240311-22-9ovtoi.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/581049/original/file-20240311-22-9ovtoi.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/581049/original/file-20240311-22-9ovtoi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/581049/original/file-20240311-22-9ovtoi.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/581049/original/file-20240311-22-9ovtoi.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Earth’s size compared with the Moon. Distances not to scale.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/the-earth-and-moon-to-scale-royalty-free-image/136247709?phrase=earth+moon+size+comparison&adppopup=true">Laara Cerman/Leigh Righton/Stockbyte via Getty Images</a></span>
</figcaption>
</figure>
<p>So, even though the Moon is much smaller <a href="https://science.nasa.gov/sun/facts/">than the Sun</a>, it is just close enough to Earth to appear the same size as the Sun when seen from Earth. </p>
<p>For example, your pinky finger is much, much smaller than the Sun, but if you hold it up at arm’s length, it appears to your eye to be large enough to block out the Sun. The Moon can do the same thing – it can block out the Sun if it’s lined up perfectly with the Sun from your point of view. </p>
<h2>Path of totality</h2>
<p>When the Earth, Moon and Sun line up perfectly, the Moon <a href="https://science.nasa.gov/solar-system/skywatching/eclipses/solar-eclipses/2024-solar-eclipse/total-solar-eclipse-2024-the-moons-moment-in-the-sun/">casts a shadow onto the Earth</a>. Since the Moon is round, its shadow is round as it lands on Earth. The only people who see the eclipse are those in the area on Earth where the shadow lands at a given moment. </p>
<p>The Moon is continuously orbiting around the Earth, so as time goes on during the eclipse, the Moon’s shadow moves over the face of the Earth. Its shadow ends up looking like a thick line that can cover hundreds of miles in length. Astronomers call that line the <a href="https://science.nasa.gov/solar-system/skywatching/eclipses/new-nasa-map-details-2023-and-2024-solar-eclipses-in-the-us/">path of totality</a>. </p>
<p>From any given location along the path of totality, an observer can see the Sun completely eclipsed for a few minutes. Then, the shadow moves away from that location and the Sun slowly becomes more and more visible. </p>
<h2>A tilted orbit</h2>
<p>Solar eclipses don’t happen every single time the Moon passes in between Earth and the Sun. If that were the case, there would be a solar eclipse every month. </p>
<p>If you could float above the Earth’s North Pole and see the Moon’s orbit from above, you would see the Moon line up with the Sun once every time it orbits around the Earth, which is approximately once per month. From this high point of view, it looks like the Moon’s shadow should land on Earth every orbit. </p>
<p>However, if you could shift your perspective to look at the Moon’s orbit from the orbital plane, you would see that the Moon’s orbit is <a href="https://moon.nasa.gov/moon-in-motion/phases-eclipses-supermoons/overview/">tilted by about 5 degrees</a> compared with Earth’s orbit around the Sun. This tilt means that sometimes the Moon is too high and its shadow passes above the Earth, and sometimes the Moon is too low and its shadow passes below the Earth. An eclipse happens only <a href="https://svs.gsfc.nasa.gov/4324/">when the Moon is positioned just right</a> and its shadow lands on the Earth. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/JplGhSC-eGM?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">There isn’t an eclipse every time the Moon passes in front of the Sun because of the Moon’s tilted orbit around Earth.</span></figcaption>
</figure>
<p>As time goes on, the Earth and the Moon continue spinning, and <a href="https://www.youtube.com/watch?v=JplGhSC-eGM">eventually the Moon aligns with Earth’s orbit</a> around the Sun at the same moment the Moon passes between the Sun and the Earth. </p>
<p>While only certain cities are in the path of totality for this April’s eclipse, the entire U.S. is still close enough to this path that observers outside of the path of totality will see a <a href="https://nso.edu/for-public/eclipse-map-2024">partial eclipse</a>. In those locations, the Moon will appear to pass in front of part of the Sun, leaving a crescent shape of the Sun still visible at the moment of maximum eclipse.</p><img src="https://counter.theconversation.com/content/224113/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Christopher Palma does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Many people will see a dazzling eclipse this April, but these events are possible only because of the sizes and precise distances between Earth, the Moon and the Sun.Christopher Palma, Teaching Professor, Department of Astronomy & Astrophysics, Penn StateLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2213812024-03-12T17:44:46Z2024-03-12T17:44:46ZTotal solar eclipses, while stunning, can damage your eyes if viewed without the right protection<figure><img src="https://images.theconversation.com/files/580528/original/file-20240307-30-bxdz7t.jpg?ixlib=rb-1.1.0&rect=47%2C6%2C4468%2C2383&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Solar eclipses don't come around often, but make sure to view these rare events with eclipse glasses to protect your vision. </span> <span class="attribution"><a class="source" href="https://newsroom.ap.org/detail/USEclipseSchools/0f2e25e7620440c0be042b6516d1acde/photo?Query=eclipse%20viewing&mediaType=photo&sortBy=&dateRange=Anytime&totalCount=524&digitizationType=Digitized&currentItemNo=18&vs=true&vs=true">AP Photo/Charlie Riedel</a></span></figcaption></figure><p>On April 8, 2024, and for the second time in the past decade, people in the U.S. will have an opportunity to <a href="https://science.nasa.gov/eclipses/future-eclipses/eclipse-2024/">view a total solar eclipse</a>. But to do so safely, you’ll need to <a href="https://preventblindness.org/get-ready-for-the-next-eclipse/">wear proper protection</a>, or risk eye damage.</p>
<p>Earth is the only planet in our solar system where <a href="https://theconversation.com/when-the-sun-goes-dark-5-questions-answered-about-the-solar-eclipse-81308">solar eclipses can occur</a>. During these celestial events, the Moon passes between our planet and the Sun, blocking the Sun and casting a shadow over the Earth. Total eclipses rarely happen multiple times in the same region of a country during one’s lifetime. </p>
<p>The path of totality for <a href="https://science.nasa.gov/eclipses/">this spring’s eclipse</a>, where you can view the total eclipse, will extend over a 100-mile path that crosses through Mexico, Texas, New England and eastern Canada.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/fmtGqOxxmEU?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Those in the path of totality will have the opportunity to see a total solar eclipse this April.</span></figcaption>
</figure>
<p>As excitement for the celestial show grows across the country, <a href="https://www.forbes.com/sites/jamiecartereurope/2024/03/09/11-ways-to-find-your-last-minute-hotel-for-the-total-solar-eclipse---but-be-quick/?sh=415b5585f4e2">hotels in the path of totality</a> have been booked up by eclipse enthusiasts. Museums and schools have <a href="https://solarsystem.nasa.gov/embeddable-eclipse-events/">planned viewing events</a>, and researchers have developed technology for the <a href="https://astrolab.fas.harvard.edu/LightSound.html">visually impaired and those with hearing loss</a> so more people have the opportunity to experience the eclipse.</p>
<p>Seeing an eclipse is a rare and special opportunity, but <a href="https://directory.hsc.wvu.edu/Profile/28506">as an ophthalmologist</a>, I know that looking directly at the Sun, even for a few moments, can severely damage your eyes. With a few easy precautions, eclipse viewers can protect themselves from severe and irreparable eye damage and vision loss.</p>
<h2>Safe eclipse viewing</h2>
<p>This year’s eclipse will unfold over a 75-minute period, from the moment the Moon starts to partially block the Sun until it completely moves away from it again. </p>
<p>During the partial eclipse period, when the Moon is partly blocking the Sun, you should never look directly at the Sun nor through binoculars, <a href="https://www.masterclass.com/articles/how-to-photograph-a-solar-eclipse">cameras</a> or <a href="https://www.space.com/how-to-photograph-a-solar-eclipse-with-a-smartphone">cellphones</a>. Sunglasses, photographic filters, exposed color film and welding glasses will dim the sunlight, but these items do not prevent <a href="https://www.aao.org/eye-health/tips-prevention/solar-eclipse-eye-safety">eye damage from the Sun’s very intense light rays</a>. </p>
<p>Only <a href="https://preventblindness.org/solar-eclipse-glasses/">solar eclipse glasses</a> with filters designed specifically for observing the partial eclipse are safe to use. They are easily available <a href="https://www.cnn.com/cnn-underscored/outdoors/best-solar-eclipse-glasses?cid=ios_app">from a variety of sources</a>, and you can wear them by themselves or over your glasses or contact lenses. </p>
<p>Keep in mind that these safety filters will permit you to view only the eclipse, as they blacken out everything around you but the Sun itself. Before purchasing a pair, make sure your eclipse glasses are approved by the <a href="https://eclipse.aas.org/eye-safety/iso-certification">ISO 12312-2 international standard</a>.</p>
<p>Only during its <a href="https://eclipse.gsfc.nasa.gov/SEhelp/SEglossary.html">period of totality</a>, the time when the Sun is fully behind the Moon, is it safe to remove your filtered glasses – and then only with caution.</p>
<p>This year, totality will last an unusually long <a href="https://science.nasa.gov/eclipses/future-eclipses/eclipse-2024/">four and a half minutes</a>. If you leave your eclipse glasses on, you will miss seeing the Sun’s bright ring, or corona, behind the Moon. But then, as the Moon moves on, the sky will brighten and you’ll need to put the eclipse glasses back on.</p>
<h2>Eyes and light</h2>
<p>While the pupils of our eyes naturally constrict to limit bright light, and our eyes have pigments to absorb light, direct sunlight overwhelms these functions. Even viewing the Sun for a few brief moments <a href="https://theconversation.com/turn-around-bright-eyes-heres-how-to-see-the-eclipse-and-protect-your-vision-203571">can cause permanent vision loss</a>. </p>
<p>The Sun emits intense <a href="https://www.britannica.com/science/sunlight-solar-radiation">ultraviolet and infrared light</a>, which, while not visible to the human eye, can burn sensitive ocular tissues, such as the cornea and retina.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/581353/original/file-20240312-24-e55u1i.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram of an eye as viewed from the side." src="https://images.theconversation.com/files/581353/original/file-20240312-24-e55u1i.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/581353/original/file-20240312-24-e55u1i.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=486&fit=crop&dpr=1 600w, https://images.theconversation.com/files/581353/original/file-20240312-24-e55u1i.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=486&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/581353/original/file-20240312-24-e55u1i.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=486&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/581353/original/file-20240312-24-e55u1i.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=611&fit=crop&dpr=1 754w, https://images.theconversation.com/files/581353/original/file-20240312-24-e55u1i.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=611&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/581353/original/file-20240312-24-e55u1i.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=611&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The cornea is the clear front surface of the eye, which lets light in. The retina is the inner lining of the back part of the eye, which sends signals to your brain, allowing you to see.</span>
<span class="attribution"><a class="source" href="https://aapos.org/glossary/how-to-safely-view-a-solar-eclipse">American Association for Pediatric Ophthalmology and Strabismus</a></span>
</figcaption>
</figure>
<p>Corneal damage from sunlight, called <a href="https://www.mayoclinic.org/diseases-conditions/actinic-keratosis/symptoms-causes/syc-20354969">solar keratosis</a>, can blur vision and be quite painful. While the cornea can heal itself, it may require several days to get better and lead to lost time at work or school. </p>
<p>Retinal damage, called <a href="https://www.health.wa.gov.au/Articles/S_T/Solar-retinopathy">solar retinopathy</a>, occurs inside the eye. While it isn’t painful, it can be more severe than corneal damage and can dramatically impair vision. Solar retinopathy symptoms include a blind spot in one’s central vision, visual distortions and altered color vision. </p>
<p>In mild cases, these symptoms may go away, but in more severe cases, and even with treatment, <a href="https://aapos.org/glossary/how-to-safely-view-a-solar-eclipse">they may become permanent</a>. </p>
<p>To both enjoy the eclipse and prevent eye damage, make sure you and your loved ones all view the event with strict proper precautions.</p><img src="https://counter.theconversation.com/content/221381/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Geoffrey Bradford does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Now’s the time to get your hands on a pair of eclipse glasses in preparation for April’s display of celestial wonder.Geoffrey Bradford, Professor of Pediatrics and Ophthalmology, West Virginia UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2227092024-03-11T20:26:45Z2024-03-11T20:26:45ZArcheoastronomy uses the rare times and places of previous total solar eclipses to help us measure history<figure><img src="https://images.theconversation.com/files/580911/original/file-20240311-28-ygi764.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C1280%2C1280&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A photograph of the 2017 total solar eclipse, taken at the Oregon State Fair Grounds, Salem, Ore.</span> <span class="attribution"><span class="source">(Dominic Hart/NASA)</span></span></figcaption></figure><p>In 648 BCE, the Greek poet Archilochus wrote that, “nothing can be surprising any more or impossible or miraculous, now that Zeus, father of the Olympians has <a href="https://articles.adsabs.harvard.edu/pdf/2020JAHH...23...47S">made night out of noonday</a>, hiding the light of the gleaming Sun.”</p>
<p>Total solar eclipses have fascinated and terrified people for centuries. Today, we know that total solar eclipses — like the <a href="https://theconversation.com/on-april-8-2024-parts-of-ontario-quebec-the-maritimes-and-newfoundland-will-see-a-total-eclipse-of-the-sun-heres-how-to-get-ready-for-it-203382">upcoming eclipse on April 8</a> — are caused by a cosmic coincidence when the moon comes between the Earth and the sun, momentarily blocking the sun from view. But in ancient times, the cause was unknown.</p>
<p>Nevertheless, the peoples of those eras took note. From all ends of the Earth, stories abound of day turning to night or <a href="https://eclipse2017.nasa.gov/eclipse-history">the sun being consumed</a>, and these records are opening up a new branch of study.</p>
<p><a href="https://www.jstor.org/stable/20170165">Astroarcheology</a> — also called archeoastronomy — uses astronomical records to help date key moments or events in history. Of all astronomical phenomena, total solar eclipses are among the best measuring sticks because they are only visible at a certain time and place. </p>
<p>Total solar eclipses are rare enough that a given spot on Earth is only likely to see <a href="https://articles.adsabs.harvard.edu/pdf/1982JBAA...92..124M">one every 375 years (on average)</a>. And when an eclipse does happen, it only appears as total to those who are <a href="https://eclipsewise.com/solar/SEatlas/SEatlas.html">along a narrow path on Earth</a>. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/580844/original/file-20240310-26-te2a9p.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="(drawing of a solar eclipse represented by a black circle surrounded by a white aura on a black background)" src="https://images.theconversation.com/files/580844/original/file-20240310-26-te2a9p.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/580844/original/file-20240310-26-te2a9p.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=464&fit=crop&dpr=1 600w, https://images.theconversation.com/files/580844/original/file-20240310-26-te2a9p.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=464&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/580844/original/file-20240310-26-te2a9p.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=464&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/580844/original/file-20240310-26-te2a9p.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=583&fit=crop&dpr=1 754w, https://images.theconversation.com/files/580844/original/file-20240310-26-te2a9p.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=583&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/580844/original/file-20240310-26-te2a9p.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=583&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">An illustration of the solar eclipse that occurred on Jan. 22, 1898 in India.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Solar_eclipse_of_January_22,_1898">(Edward Walter Maunder/British Astronomical Association)</a></span>
</figcaption>
</figure>
<h2>Identifying years</h2>
<p>This combination of rare time and place helps researchers narrow down the exact date ancient peoples viewed a recorded eclipse. Additional clues such as the time of day the eclipse occurred (morning, noon or evening), time of year (season) or the presence of bright planets can also help identify the exact eclipse.</p>
<p>For example, a record of total solar eclipse occurring near dawn in ancient Chinese texts pertaining to King Yi helped <a href="https://articles.adsabs.harvard.edu/pdf/2003JAHH....6...53L">identify the year his reign began</a>.</p>
<p>One of the oldest recorded eclipses is on a clay tablet from the city of <a href="https://www.britannica.com/place/Ugarit">Ugarit, in modern-day Syria</a>. The city was overthrown after the eclipse, making the tablet one of the last things written down by someone from that city. The inscription on the tablet reads: “… day of the new moon in ḫiyaru the Sun went down, its gate-keeper was [Rashap].”</p>
<p>The word ḫiyaru refers to a time of year around February/March, and Rashap is likely a planet. Armed with this information and knowledge that the city disappeared in the Bronze Age, researchers dated the tablet and eclipse to March 5, 1222 BCE, over 3,000 years ago, with the planet Mars <a href="https://doi.org/10.1038/338238a0">visible near to the eclipsed sun</a>. Thanks to this eclipse, we know that Ugarit fell after March 5, 1222 BCE. </p>
<p>Records like these help researchers identify precise dates in the ancient world.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/580919/original/file-20240311-17800-m97ekg.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="an illustration of text above a photograph of a grey clay tablet" src="https://images.theconversation.com/files/580919/original/file-20240311-17800-m97ekg.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/580919/original/file-20240311-17800-m97ekg.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=689&fit=crop&dpr=1 600w, https://images.theconversation.com/files/580919/original/file-20240311-17800-m97ekg.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=689&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/580919/original/file-20240311-17800-m97ekg.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=689&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/580919/original/file-20240311-17800-m97ekg.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=866&fit=crop&dpr=1 754w, https://images.theconversation.com/files/580919/original/file-20240311-17800-m97ekg.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=866&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/580919/original/file-20240311-17800-m97ekg.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=866&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Photograph and illustration of the clay tablet KTU 1.78 from Ugarit, in modern-day Syria, which mentions a total solar eclipse.</span>
<span class="attribution"><span class="source">(Dietrich and Loretz/University of Chicago Library)</span></span>
</figcaption>
</figure>
<h2>Changing predictions</h2>
<p>Precisely predicting future eclipses, or plotting the paths of historical eclipses, requires knowing the positions of the sun, moon and Earth. Computers can track the motions of each, but the challenge here is that these motions are not constant. As the moon causes tides in Earth’s oceans, the process also causes the moon to slowly drift away from the Earth and <a href="https://www.scientificamerican.com/article/earth-rotation-summer-solstice/">the length of day on Earth to slowly increase</a>. </p>
<p>Essentially, the length of a day on Earth is getting longer by roughly 18 microseconds every year, <a href="http://dx.doi.org/10.1098/rspa.2016.0404">or one second every 55,000 years</a>. After hundreds or thousands of years, that fraction of a second per day adds up to several hours.</p>
<p>The change in Earth’s day also affects dating historical eclipses — if the difference in the length of day is not corrected for, calculations may be inaccurate by thousands of kilometers. As such, when using eclipses to date historical events a correction must be applied; uncertainties in the correction can make <a href="https://doi.org/10.1093/pasj/56.1.215">ancient eclipse identifications</a> harder to pin down in the absence of <a href="https://www.jstor.org/stable/178278">additional information</a> to help <a href="https://articles.adsabs.harvard.edu/pdf/1995QJRAS..36..397Z">narrow down the possibilities</a>. </p>
<h2>Measuring changing day-lengths</h2>
<p>For those solar eclipses that are well established, they open a window into tracking Earth’s length-of-day across the centuries. By timing eclipses over the last 2,000 years, researchers have mapped out the length of Earth’s day over that same span. The value of 18 microseconds per year is an average, but sometimes the Earth slows down a bit more and sometimes a bit less. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/580922/original/file-20240311-139405-bs1pct.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="a graph showing day lengths over time" src="https://images.theconversation.com/files/580922/original/file-20240311-139405-bs1pct.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/580922/original/file-20240311-139405-bs1pct.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=413&fit=crop&dpr=1 600w, https://images.theconversation.com/files/580922/original/file-20240311-139405-bs1pct.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=413&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/580922/original/file-20240311-139405-bs1pct.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=413&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/580922/original/file-20240311-139405-bs1pct.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=518&fit=crop&dpr=1 754w, https://images.theconversation.com/files/580922/original/file-20240311-139405-bs1pct.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=518&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/580922/original/file-20240311-139405-bs1pct.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=518&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Change in length of day (lod) for Earth in milliseconds (0.001 s) as measured from eclipse records (black line). The red line shows the average change over 2,000 years, while the grey line shows what we would expect from tidal forces between the Earth and moon only. The green dashed line shows a model fit to the data in black.</span>
<span class="attribution"><a class="source" href="http://dx.doi.org/10.1098/rspa.2016.0404">(F.R. Stephenson, L.V. Morrison and C.Y. Hohenkerk)</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Tides alone can’t explain this pattern — there is something more going on between the moon and the Earth, and the cause is still unknown. This mystery, however, can be explored thanks to solar eclipses. </p>
<p>We can measure a change in length of a day on Earth with instruments now, but we wouldn’t be able to capture that change hundreds or thousands of years back in time without a precise measuring stick and records of eclipses over millennia and across the world. Total solar eclipses allow us to peer into not only our own history, but the history of the Earth itself.</p><img src="https://counter.theconversation.com/content/222709/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Sarah Sadavoy receives funding from the National Sciences and Engineering Research Council of Canada (NSERC). </span></em></p>Mentions of total solar eclipses in ancient history help researchers pinpoint precise dates of notable events.Sarah Sadavoy, Assistant Professor, Physics, Engineering Physics & Astronomy, Queen's University, OntarioLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2208242024-03-08T14:35:38Z2024-03-08T14:35:38ZApril’s eclipse will mean interruptions in solar power generation, which could strain electrical grids<figure><img src="https://images.theconversation.com/files/573902/original/file-20240206-16-om8k0f.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C3994%2C2658&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Solar panels in Brazil. </span> <span class="attribution"><a class="source" href="https://newsroom.ap.org/detail/7551d26521224cbf94340e255374a7a7?ext=true">AP Photo/Bruna Prado</a></span></figcaption></figure><p>During the most recent total solar eclipse visible in the U.S., on Aug. 21, 2017, the skies darkened as the Moon crossed in front of the Sun. It blocked out all sunlight – except for that from a golden ring visible around the Moon’s shape, called the corona. Not surprisingly, solar power generation across North America plummeted for several hours, from the first moment the Moon began to obscure the Sun to when the Sun’s disk was clear again. </p>
<p>On April 8, 2024, another <a href="https://theconversation.com/when-the-sun-goes-dark-5-questions-answered-about-the-solar-eclipse-81308">total solar eclipse</a> will track across the U.S., causing perhaps an even greater loss of solar power generation. Although this will be the second total solar eclipse visible in the U.S. in under seven years, these events are a rare occurrence. Nevertheless, they present a unique challenge to power grid operators.</p>
<p><a href="https://dornsife.usc.edu/profile/vahe-peroomian/">I am a space scientist</a> with a passion for teaching physics and astronomy. Though I have seen many partial eclipses of the Sun, I have yet to witness a total solar eclipse. My road trip to Bryce Canyon National Park in Utah in October 2023 to see the “ring of fire” <a href="https://theconversation.com/explainer-what-is-a-solar-eclipse-33019">annular solar eclipse</a> was unforgettable, and April 8 will surely find me handing out <a href="https://theconversation.com/turn-around-bright-eyes-heres-how-to-see-the-eclipse-and-protect-your-vision-203571">eclipse glasses</a> once again.</p>
<h2>When the Moon’s shadow blocks the Sun</h2>
<p>During <a href="https://theconversation.com/explainer-what-is-a-solar-eclipse-33019">a solar eclipse</a>, the Moon partially or completely blocks the view of the Sun. Since the Moon is nearly 400 times smaller than the Sun and nearly <a href="https://www.universetoday.com/17109/the-sun-and-the-moon/">400 times closer</a>, the <a href="https://www.forbes.com/sites/startswithabang/2017/02/08/the-strangest-eclipse-fact-of-all-the-moons-shadow-isnt-a-circle/?sh=be76f8c17bd3">Moon’s shadow</a>, visible from Earth, tapers to a width of <a href="https://cmase.uark.edu/_resources/pdf/nasa/NASAConnect/pathoftotality.pdf">70 to 100 miles</a> (112 to 161 kilometers).</p>
<p>Within this region, called the path of totality, observers see a total solar eclipse. Observers close to but outside this path witness a partial eclipse of the Sun, where the Moon covers a fraction of the Sun’s disk. </p>
<p>During the April 8, 2024, total solar eclipse, the <a href="https://science.nasa.gov/eclipses/future-eclipses/eclipse-2024/where-when/">path of totality</a> in the continental U.S. will extend from Texas in the south to Maine in the northeast. Elsewhere in the U.S., Miami will see a partial eclipse in which a maximum of 46% of the Sun’s disk is obscured. In Seattle, far from the path of totality, the Moon will cover only a maximum of <a href="https://www.timeanddate.com/eclipse/map/2024-april-8">20% of the Sun</a>. In southern Texas, where the path of totality first crosses into the U.S., the eclipse will last just under three hours, with totality a mere 4 minutes and 27 seconds. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/sOpYoO_SK7o?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The path of the 2024 solar eclipse.</span></figcaption>
</figure>
<h2>Increasing reliance on solar power</h2>
<p>The worldwide trend toward renewable energy has seen a significant increase in solar, or photovoltaic, power generation in the last decade. Solar power generation capacity is set to <a href="https://www.iea.org/data-and-statistics/data-tools/renewable-energy-progress-tracker">double worldwide</a> between 2022 and 2028, and the U.S. now has the capacity to generate <a href="https://ember-climate.org/data-catalogue/yearly-electricity-data/">three times more solar energy</a> than at the time of the 2017 total solar eclipse.</p>
<p>The most obvious obstacle to solar power generation is cloud cover. On a cloudy day, the energy produced by solar panels drops to <a href="https://www.forbes.com/home-improvement/solar/solar-panels-cloudy-days-night/">10% to 25%</a> of its output on a sunny day. </p>
<p>The North American power transmission grid is divided into <a href="https://www.nerc.com/AboutNERC/keyplayers/Pages/default.aspx">six major regions</a> and <a href="https://alternativeenergy.procon.org/questions/what-is-the-electricity-grid/">more than 150</a> local and regional subgrids. Electrical system operators in each local grid continuously balance the amount of electricity production with the “load,” or the demand for electricity by consumers. </p>
<p>System operators can tap into energy from <a href="https://science.howstuffworks.com/environmental/energy/power.htm">various power generation mechanisms</a> like solar, wind, hydroelectric, natural gas and coal. Local grids can also import and export electricity to and from their grid as needed.</p>
<p>System operators have accurate models for the amount of solar power generated across the U.S. on a daily basis, and these models account for the parts of the continental U.S. that may have cloudy skies. By pairing solar power generation with battery storage, they can access electricity from solar even when the Sun isn’t shining – on cloudy days or at night. </p>
<p>To plan for an eclipse, electrical system operators need to figure out how much the energy production will drop and how much power people will draw from the reserves. On the day of the 2017 total solar eclipse, for example, solar power generation in the U.S. <a href="https://www.nrel.gov/docs/fy18osti/71147.pdf">dropped 25%</a> below average. </p>
<p>Because solar power production falls quickly during the eclipse’s peak, grid operators may need to tap into reserves at a rate that may strain the <a href="https://www.osha.gov/etools/electric-power/illustrated-glossary/transmission-lines">electrical transmission lines</a>. To try to keep things running smoothly, grid operators will rely on local reserves and minimize power transfer <a href="https://www.nrel.gov/docs/fy18osti/71147.pdf">between grids</a> during the event. This should lessen the burden on transmission lines in local grids and prevent temporary blackouts. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/573903/original/file-20240206-28-khlo8k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Electrical towers and power lines shown against a sunset." src="https://images.theconversation.com/files/573903/original/file-20240206-28-khlo8k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/573903/original/file-20240206-28-khlo8k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/573903/original/file-20240206-28-khlo8k.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/573903/original/file-20240206-28-khlo8k.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/573903/original/file-20240206-28-khlo8k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/573903/original/file-20240206-28-khlo8k.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/573903/original/file-20240206-28-khlo8k.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Solar eclipses can stress the power grid.</span>
<span class="attribution"><a class="source" href="https://newsroom.ap.org/detail/BidenInfrastructure/9a4ee5858ac74db78eb7d96b1961c275/photo?Query=power%20grid&mediaType=photo&sortBy=&dateRange=Anytime&totalCount=226&digitizationType=Digitized&currentItemNo=17&vs=true&vs=true">AP Photo/Matt Rourke</a></span>
</figcaption>
</figure>
<h2>Renewable energy during eclipses</h2>
<p>Solar isn’t the only type of renewable energy generation that goes down during an eclipse. Since it’s not as sunny, temperatures along the path of the eclipse fall by as much as <a href="https://eclipse2017.nasa.gov/temperature-change-during-totality">10 degrees Fahrenheit</a> (5.5 degrees Celsius). Lower temperatures lead to <a href="https://doi.org/10.1093/astrogeo/atx135">slower wind speeds</a> and less wind power generation. </p>
<p>During the August 2017 eclipse, the loss of renewable power generation added up to nearly <a href="https://www.nrel.gov/docs/fy18osti/71147.pdf">6 gigawatts</a>. That’s equivalent to the energy usage of <a href="https://www.energy.gov/eere/articles/how-much-power-1-gigawatt">600 million LED lightbulbs</a> or <a href="https://www.cnet.com/home/energy-and-utilities/gigawatt-the-solar-energy-term-you-should-know-about/">4.5 million homes</a>. </p>
<p>Grid operators compensated by planning ahead and increasing power generation at <a href="https://www.nrel.gov/docs/fy18osti/71147.pdf">natural gas and coal-powered plants</a>, which don’t depend on sunlight. </p>
<p>Over the duration of the eclipse, this increase in nonrenewable energy use led to approximately <a href="https://www.eia.gov/tools/faqs/faq.php?id=74&t=11">10 million pounds</a> of extra carbon dioxide emissions. That’s about the annual carbon dioxide emissions of 1,000 cars.</p>
<p>On April 8, <a href="https://theconversation.com/astro-tourism-chasing-eclipses-meteor-showers-and-elusive-dark-skies-from-earth-207969">eyes across the U.S. will turn upward</a> to catch a glimpse of the eclipsed Sun.</p>
<p>Thanks to the vigilance of electric grid operators, the lights should stay on, and observers won’t have to worry about anything but the stunning show in the sky.</p><img src="https://counter.theconversation.com/content/220824/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Vahe Peroomian has, in the past, received basic research funding from NASA and the National Science Foundation.</span></em></p>When the Moon blocks the Sun during an eclipse, utility suppliers have to pull power from the grid to make up for gaps in solar energy.Vahe Peroomian, Professor of Physics and Astronomy, USC Dornsife College of Letters, Arts and SciencesLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2211552024-03-07T13:03:45Z2024-03-07T13:03:45ZWhy schools need to take sun safety more seriously – expert explains<figure><img src="https://images.theconversation.com/files/577546/original/file-20240223-16-azytla.jpg?ixlib=rb-1.1.0&rect=37%2C0%2C4195%2C2788&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The World Health Organization recommends formal school programmes as the key to preventing skin cancer.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/young-boy-having-sunscreen-applied-339150182">Paul Higley/Shutterstock</a></span></figcaption></figure><p>Despite the UK’s rainy climate, there is a one in six <a href="https://onlinelibrary.wiley.com/doi/10.1002/ski2.61">risk</a> of developing skin cancer. Children, especially, should take extra care as severe sunburn as a youngster more than <a href="https://www.skincancer.org/risk-factors/sunburn/">doubles</a> the chance of developing skin cancer later on. </p>
<p>But <a href="https://academic.oup.com/ced/advance-article/doi/10.1093/ced/llad458/7507665">new research</a> my colleagues and I conducted shows that less than half of primary schools in Wales have a formal sun safety policy.</p>
<p>With skin cancer rates continuing to rise by <a href="https://gettingitrightfirsttime.co.uk/medical_specialties/dermatology/">8% annually</a> in England and Wales, it’s a problem that’s not going away and the disease now accounts for half of all cancers. In 2020 alone, the cost of treating skin cancer in England was <a href="https://pubmed.ncbi.nlm.nih.gov/23554510/">estimated</a> to be more than £180 million.</p>
<p>There is hope, though. It is estimated that around <a href="https://www.skincancer.org/skin-cancer-information/skin-cancer-facts">90% of skin cancers</a> are due to ultraviolet (UV) radiation exposure from the sun. This means they can be prevented through safer behaviour. </p>
<p>In the UK, though, many people still <a href="https://academic.oup.com/her/article/20/5/579/611761">underestimate</a> the link between sunburn and skin cancer. Research paints a worrying picture, revealing disparities in sun protection awareness and behaviour across different groups. Notably, <a href="https://academic.oup.com/her/article/20/5/579/611761">men</a>, people living in <a href="https://pubmed.ncbi.nlm.nih.gov/26875569/">low-income neighbourhoods</a>, those belonging to <a href="https://academic.oup.com/her/article/20/5/579/611761">lower socioeconomic groups</a> and <a href="https://pubmed.ncbi.nlm.nih.gov/28125871/">people of colour</a> are often found to be less informed about sun safety and are more likely to put themselves at risk. </p>
<p>With childhood a crucial time for learning healthy behaviour, teaching all children from a young age about sun protection could be one way to reduce future skin cancer rates. And the <a href="https://iris.who.int/bitstream/handle/10665/42678/9241590629_v1.pdf?sequence=1">World Health Organization</a> recommends formal school programmes as the key to prevention. </p>
<p>Overall, school-based interventions have been <a href="https://www.sciencedirect.com/science/article/pii/S0091743521000438">shown</a> to positively influence sun safe knowledge and behaviour. For example, <a href="https://doi.org/10.1093/her/cyt105">schools in Australia</a> with written policies show better sun protection practices than those without.</p>
<p>But in UK schools, the situation varies. The UK government’s Department for Education has issued <a href="https://www.gov.uk/government/publications/relationships-education-relationships-and-sex-education-rse-and-health-education/physical-health-and-mental-wellbeing-primary-and-secondary#by-the-end-of-primary-school">statutory guidance</a> for England that children should leave primary school knowing about sun safety and how to reduce the risk of getting skin cancer. </p>
<p>In Scotland and Northern Ireland, it is not a legal requirement to teach sun safety in schools. And in Wales, while sun safety is recommended as part of the Welsh Network of Healthy Schools scheme, again there is no mandatory requirement to have a sun safety policy or to teach skin cancer prevention. Nor are there central UK resources provided to help schools in this area. </p>
<figure class="align-center ">
<img alt="The red, peeling sunburnt back and shoulders of a young girl." src="https://images.theconversation.com/files/578006/original/file-20240226-21-2xd3jb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/578006/original/file-20240226-21-2xd3jb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/578006/original/file-20240226-21-2xd3jb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/578006/original/file-20240226-21-2xd3jb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/578006/original/file-20240226-21-2xd3jb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/578006/original/file-20240226-21-2xd3jb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/578006/original/file-20240226-21-2xd3jb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=501&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Being severely sunburnt as a youngster more than doubles the chance of developing future skin cancer.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/dangerous-sunburn-shoulders-young-girl-601094933">Alonafoto/Shutterstock</a></span>
</figcaption>
</figure>
<p>My colleagues and I wanted to know how many schools have a sun safety policy, a formal document that sets out a school’s position with respect to the education and provision of sun safety. We also wanted to understand whether the existence of a policy varied by area or school characteristic, and what support schools need. </p>
<p>In 2022, we sent a survey to all 1,241 primary schools in Wales. In total, 471 schools responded. </p>
<h2>What we found</h2>
<p>We found that only 39% of responding schools had a formal sun safety policy. And of these, not all enforced them. Schools that had more children receiving free school meals and with lower attendance rates were less likely to have a sun safety policy.</p>
<p>We asked schools that did not have a policy to tell us the reasons why not. Thirty-five per cent of schools were “not aware of the need”, while 27% of schools had “not got around to it just yet”. Thirty schools (13%) said that a sun safety policy was not a priority at this time. Clearly, there is work to be done on raising awareness among schools and school leaders on the role they can play in this area.</p>
<p>Of course, schools are busy places. So, when asked to indicate what would encourage them to create a sun safety policy, 73% of schools said assistance with development, while 56% said resources to aid the teaching of sun safety. </p>
<p>Previously both Cancer Research UK and the Wales-based Tenovus Cancer Care charities have offered support and guidelines for schools but this support is no longer easily available. The England-based charity <a href="https://www.skcin.org/ourWork/sunSafeSchools.htm">Sckin</a> has a comprehensive and free sun-safe schools accreditation scheme. Some schools told us they based their policies on resources supplied by the local authority, but this was not consistent across Wales.</p>
<p>UV levels will soon rise in the UK and now is the time for schools to start thinking about sun protection. Having a formal sun safety school policy sets out the position of the school when it comes to sun safety. When enforced and communicated properly, this makes it clear to everyone (governors, teachers, carers and pupils) their individual responsibilities when it comes to staying safe. </p>
<p>But with fewer than half of schools in Wales having formal policies, and not all enforced, awareness of the importance of this issue and the potential role of schools is lacking. </p>
<p>It is therefore time for sun safety policies to become mandatory for primary schools across the UK. This could help to improve knowledge and behaviour for all age groups. But adequate support and guidance must be also given to schools to help them educate children about sun safety and protect them while they are at school.</p><img src="https://counter.theconversation.com/content/221155/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Julie Peconi received funding for the Sunproofed Study from Health and Care Research Wales through a Health Research Grant Award. She is also a volunteer with the charity Skin Care Cymru, a charity working to raise the profile of skin health in Wales. </span></em></p>Being severely sunburnt as a child more than doubles the chance of developing future skin cancer but less than half of primary schools questioned in new research have a sun safety policy.Julie Peconi, Senior Research Officer in Health Data Science, Swansea UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2245032024-02-28T01:00:24Z2024-02-28T01:00:24ZLeap of imagination: how February 29 reminds us of our mysterious relationship with time and space<p>If you find it intriguing that February 28 will be followed this week by February 29, rather than March 1 as it usually is, spare a thought for those alive in 1582. Back then, Thursday October 4 was followed by Friday October 15.</p>
<p>Ten whole days were snatched from the present when Pope Gregory XIII issued a papal bull to “restore” the calendar from discrepancies that had crept into the Julian calendar, introduced by Julius Caesar in 45 BCE.</p>
<p>The new Gregorian calendar returned the northern hemisphere’s vernal equinox to its “proper” place, around March 21. (The equinox is when the Earth’s axis is tilted neither toward nor away from the sun, and is used to determine the date of Easter.) </p>
<p>The Julian calendar had observed a leap year every four years, but this meant time had drifted out of alignment with the dates of celestial events and astronomical seasons. </p>
<p>In the Gregorian calendar, leap days were added only to years that were a multiple of four – like 2024 – with an exception for years that were evenly divisible by 100, but not 400 – like 1700.</p>
<p>Simply put, leap days exist because it doesn’t take a neat 365 days for Earth to orbit the Sun. It takes 365.2422 days. Tracking the movement of celestial objects through space in an orderly pattern doesn’t quite work, which is why we have February – time’s great mop.</p>
<h2>Time and space</h2>
<p>This is just part of the history of how February – the shortest month, and originally the last month in the Roman calendar – came to have the job of absorbing those inconsistencies in the temporal calculations of the world’s most commonly used calendar.</p>
<p>There is plenty of <a href="https://theconversation.com/leap-day-fixing-the-faults-in-our-stars-54032">science</a>, <a href="https://theconversation.com/explainer-the-science-behind-leap-years-and-how-they-work-54788">maths</a> and <a href="https://theconversation.com/how-a-seasonal-snarl-up-in-the-mid-1500s-gave-us-our-strange-rules-for-leap-years-132659">astrophysics</a> explaining the relationship between time and the planet we live on. But I like to think leap years and days offer something even more interesting to consider: why do we have calendars anyway?</p>
<p>And what have they got to do with how we understand the wonder and strangeness of our existence in the universe? Because calendars tell a story, not just about time, but also about space.</p>
<p>Our reckoning of time on Earth is through our spatial relationship to the Sun, Moon and stars. Time, and its place in our lives, sits somewhere between the scientific, the celestial and the spiritual. </p>
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<p>
<em>
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Read more:
<a href="https://theconversation.com/why-does-a-leap-year-have-366-days-218330">Why does a leap year have 366 days?</a>
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</p>
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<p>It is <a href="https://shop.whitechapelgallery.org/products/time">notoriously slippery, subjective and experiential</a>. It is also marked, tracked and determined in myriad ways across different cultures, from tropical to solar to <a href="https://www.stuff.co.nz/pou-tiaki/300062097/matariki-and-the-maramataka-the-mori-lunar-calendar">lunar</a> calendars.</p>
<p>It is the Sun that measures a day and gives us our first reference point for understanding time. But it is the <a href="https://librarysearch.aut.ac.nz/vufind/Record/1145999?sid=25214690">Moon</a>, as a major celestial body, that extends our perception of time. By stretching a span of one day into something longer, it offers us a chance for philosophical reflection.</p>
<p>The Sun (or its effect at least) is either present or not present. The Moon, however, goes through phases of transformation. It appears and disappears, changing shape and hinting that one night is not exactly like the one before or after.</p>
<p>The Moon also has a distinct rhythm that can be tracked and understood as a pattern, giving us another sense of duration. Time is just that – overlapping durations: instants, seconds, minutes, hours, days, weeks, months, years, decades, lifetimes, centuries, ages.</p>
<h2>The elusive Moon</h2>
<p>It is almost impossible to imagine how time might feel in the absence of all the tools and gadgets we use to track, control and corral it. But it’s also hard to know what we might do in the absence of time as a unit of productivity – a measurable, dispensable resource.</p>
<p>The closest we might come is simply to imagine what life might feel like in the absence of the Moon. Each day would rise and fall, in a rhythm of its own, but without visible reference to anything else. Just endless shifts from light to dark.</p>
<p>Nights would be almost completely dark without the light of the Moon. Only stars at a much further distance would puncture the inky sky. The world around us would change – trees would grow, mammals would age and die, land masses would shift and change – but all would happen in an endless cycle of sunrise to sunset.</p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/scientists-are-hoping-to-redefine-the-second-heres-why-157645">Scientists are hoping to redefine the second – here's why</a>
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<p>The light from the Sun takes <a href="https://www.skyatnightmagazine.com/space-science/how-take-light-from-sun-reach-earth">eight minutes</a> to reach Earth, so the sunlight we see is always eight minutes in the past. </p>
<p>I remember sitting outside when I first learned this, and wondering what the temporal delay might be between me and other objects: a plum tree, trees at the end of the street, hills in the distance, light on the horizon when looking out over the ocean, stars in the night sky.</p>
<p>Moonlight, for reference, takes about <a href="https://www.pbs.org/seeinginthedark/astronomy-topics/light-as-a-cosmic-time-machine.html">1.3 seconds</a> to get to Earth. Light always travels at the same speed, it is entirely constant. The differing duration between how long it takes for sunlight or moonlight to reach the Earth is determined by the space in between. </p>
<p>Time on the other hand, is anything but constant. There are countless ways we characterise it. The mere fact we have so many calendars and ways of describing perceptual time hints at our inability to pin it down. </p>
<p>Calendars give us the impression we can, and have, made time predictable and understandable. Leap years, days and seconds serve as a periodic reminder that we haven’t.</p><img src="https://counter.theconversation.com/content/224503/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Emily O'Hara does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>2024 is a leap year, when the shortest month mops up a bit of leftover time. But the extra day also tells us about space – and our place in it.Emily O'Hara, Senior Lecturer, Spatial Design + Temporary Practices, Auckland University of TechnologyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2183302024-02-19T13:36:56Z2024-02-19T13:36:56ZWhy does a leap year have 366 days?<figure><img src="https://images.theconversation.com/files/575717/original/file-20240214-24-h6q6if.jpg?ixlib=rb-1.1.0&rect=38%2C23%2C5137%2C3422&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Leap Day is coming.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/calendar-on-february-29-on-a-leap-year-leap-day-royalty-free-image/1196849410">Marvin Samuel Tolentino Pineda/iStock, via Getty images</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p>Why does a leap year have 366 days? Does the Earth move slower every four years? – Aarush, age 8, Milpitas, California</p>
</blockquote>
<hr>
<p>You may be used to hearing that it takes the Earth 365 days to make a full lap, but that journey actually lasts about 365 and a quarter days. Leap years help to keep the 12-month calendar matched up with Earth’s movement around the Sun. </p>
<p>After four years, those leftover hours add up to a whole day. In a leap year, we add this extra day to the month of February, making it 29 days long instead of the usual 28.</p>
<p>The idea of an annual catch-up dates back to ancient Rome, where people had a calendar with 355 days instead of 365 because it was based on cycles and phases of the Moon. They noticed that their calendar was getting out of sync with the seasons, so they began adding an extra month, <a href="https://www.britannica.com/science/Roman-republican-calendar">which they called Mercedonius</a>, every two years to catch up with the missing days.</p>
<p>In the year 45 B.C.E., Roman emperor Julius Caesar introduced a solar calendar, based on one developed in Egypt. Every four years, February received an extra day to keep the calendar in line with the Earth’s journey around the Sun. In honor of Caesar, this system is still known as the Julian calendar.</p>
<p>But that wasn’t the last tweak. As time went on, people realized that the Earth’s journey wasn’t exactly 365.25 days – it <a href="https://airandspace.si.edu/stories/editorial/science-leap-year">actually took 365.24219 days</a>, which is about 11 minutes less. So adding a whole day every four years was actually a little more correction than was needed. </p>
<p>In 1582, Pope Gregory XIII signed an order that made a small adjustment. There would still be a leap year every four years, except in “century” years – years divisible by 100, like 1700 or 2100 – unless they were also divisible by 400. It might sound a bit like a puzzle, but this adjustment made the calendar <a href="https://airandspace.si.edu/stories/editorial/science-leap-year">even more accurate</a> – and from that point on, it was known as the Gregorian calendar.</p>
<h2>What if we didn’t have leap years?</h2>
<p>If the calendar didn’t make that small correction every four years, it would gradually fall out of alignment with the seasons. Over centuries, this could lead to the <a href="https://www.britannica.com/story/whats-the-difference-between-a-solstice-and-an-equinox">solstices and equinoxes</a> occurring at different times than expected. Winter weather might develop in what the calendar showed as summer, and farmers could become confused about when to plant their seeds.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/YTOr8_ILqGw?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Without leap years, our calendar would gradually become disconnected from the seasons.</span></figcaption>
</figure>
<p>Other calendars around the world have their own ways of keeping time. The Jewish calendar, which is regulated by <a href="https://www.britannica.com/topic/Jewish-religious-year">both the Moon and the Sun</a>, is like a big puzzle with a 19-year cycle. Every now and then, it adds a leap month to make sure that special celebrations happen at just the right time. </p>
<p>The <a href="https://ing.org/resources/for-all-groups/calendar-of-important-islamic-dates/">Islamic calendar</a> is even more unusual. It follows the <a href="https://spaceplace.nasa.gov/moon-phases/en/">phases of the Moon</a> and doesn’t add extra days. Since a lunar year is only about 355 days long, key dates on the Islamic calendar move 10 to 11 days earlier each year on the solar calendar. </p>
<p>For example, Ramadan, the <a href="https://ing.org/resources/for-all-groups/calendar-of-important-islamic-dates/">Islamic month of fasting</a>, falls in the ninth month of the Islamic calendar. In 2024, it will run from March 11 to April 9; in 2025, it will occur from March 1-29; and in 2026, it will be celebrated from Feb. 18 to March 19.</p>
<h2>Learning from the planets</h2>
<p>Astronomy originated as a way to make sense of our daily lives, linking the events around us to celestial phenomena. The concept of leap years exemplifies how, from early ages, humans found order in conditions that seemed chaotic. </p>
<p>Simple, unsophisticated but effective tools, born from creative ideas of ancient astronomers and visionaries, provided the first glimpses into understanding the nature that envelops us. Some <a href="https://www.britannica.com/science/astronomy/History-of-astronomy">ancient methods</a>, such as <a href="https://sci.esa.int/web/gaia/-/53196-the-oldest-sky-maps">astrometry and lists of astronomical objects</a>, persist even today, revealing the timeless essence of our quest to understand nature. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/575719/original/file-20240214-30-of8z7y.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Photograph of an intricate schematic guide to the night sky." src="https://images.theconversation.com/files/575719/original/file-20240214-30-of8z7y.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/575719/original/file-20240214-30-of8z7y.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=356&fit=crop&dpr=1 600w, https://images.theconversation.com/files/575719/original/file-20240214-30-of8z7y.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=356&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/575719/original/file-20240214-30-of8z7y.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=356&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/575719/original/file-20240214-30-of8z7y.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=447&fit=crop&dpr=1 754w, https://images.theconversation.com/files/575719/original/file-20240214-30-of8z7y.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=447&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/575719/original/file-20240214-30-of8z7y.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=447&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Ancient Egyptians were dedicated astronomers. This section from the ceiling of the tomb of Senenmut, a high court official in Egypt, was drawn sometime circa 1479–1458 B.C.E. It shows constellations, protective gods and 24 segmented wheels for the hours of the day and the months of the year.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Senenmut-Grab.JPG">NebMaatRa/Wikimedia</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
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<p>People who do research in physics and astronomy, the <a href="https://scholar.google.com/citations?user=t4L_D18AAAAJ&hl=en">field that I study</a>, are inherently curious about the workings of the universe and our origins. This work is exciting, and also extremely humbling; it constantly shows that in the grand scheme, our lives occupy a mere second in the vast expanse of space and time – even in leap years when we add that extra day.</p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/218330/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Bhagya Subrayan does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Humans have synced their calendars to the sun and moon for centuries, but every so often, these systems need a little correction.Bhagya Subrayan, PhD Student in Physics and Astronomy, Purdue UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2198922024-02-05T13:30:46Z2024-02-05T13:30:46ZUS Moon landing marks new active phase of lunar science, with commercial launches of landers that will study solar wind and peer into the universe’s dark ages<figure><img src="https://images.theconversation.com/files/567940/original/file-20240104-21-s3p58r.jpg?ixlib=rb-1.1.0&rect=4%2C17%2C2991%2C1868&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The dark, far side of the Moon is the perfect place to conduct radio astronomy. </span> <span class="attribution"><a class="source" href="https://newsroom.ap.org/detail/LunarEclipse/704e3da2df90473486270e23aa73419d/photo?Query=moon&mediaType=photo&sortBy=&dateRange=Anytime&totalCount=399&digitizationType=Digitized&currentItemNo=12&vs=true&vs=true">AP Photo/Rick Bowmer</a></span></figcaption></figure><p>For the first time since 1972, NASA <a href="https://www.intuitivemachines.com/im-1">landed a craft on the surface of the Moon</a> in February 2024. But the agency didn’t do it alone – instead, it partnered with commercial companies. Thanks to new technologies and <a href="https://www.nasa.gov/commercial-lunar-payload-services/">public-private partnerships</a>, the scientific projects brought to the Moon on this craft and on future missions like it will open up new realms of scientific possibility. </p>
<p>As parts of several projects launching this year, teams of scientists, including myself, will conduct radio astronomy from the south pole and the far side of the Moon.</p>
<p>NASA’s <a href="https://www.nasa.gov/commercial-lunar-payload-services/">commercial lunar payload services program</a>, or CLPS, will use uncrewed landers to conduct NASA’s first science experiments from the Moon in over 50 years. The CLPS program differs from past space programs. Rather than NASA building the landers and operating the program, commercial companies will do so in a public-private partnership. NASA identified <a href="https://www.nasa.gov/commercial-lunar-payload-services/clps-providers/">about a dozen companies</a> to serve as vendors for landers that will go to the Moon. </p>
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<figcaption><span class="caption">CLPS will send science payloads to the Moon in conjunction with the Artemis program’s crewed missions.</span></figcaption>
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<p>NASA buys space on these landers for <a href="https://science.nasa.gov/lunar-science/clps-deliveries/">science payloads</a> to fly to the Moon, and the companies design, build and insure the landers, as well as contract with rocket companies for the launches. Unlike in the past, NASA is one of the customers and not the sole driver. </p>
<h2>Peregrine and Odysseus, the first CLPS landers</h2>
<p>The first two CLPS payloads are scheduled to launch during the first two months of 2024. There’s the <a href="https://science.nasa.gov/lunar-science/clps-deliveries/to2-astrobotic/">Astrobotics payload</a>, which launched Jan. 8 before its lander, named Peregrine, <a href="https://www.space.com/astrobotic-peregrine-moon-lander-headed-to-earth">experienced a fuel issue</a> that cut its journey to the Moon short. </p>
<p>Next, there’s the <a href="https://science.nasa.gov/lunar-science/clps-deliveries/op-to2-intuitive-machines/">Intuitive Machines payload</a>. Intuitive Machines’ lander, named Odysseus, <a href="https://www.intuitivemachines.com/im-1">landed near the south pole of the Moon</a> on Feb. 22, 2024. NASA has also planned a <a href="https://science.nasa.gov/lunar-science/clps-deliveries/">few additional landings</a> – about two or three per year – for each of the next few years.</p>
<p>I’m a <a href="https://www.colorado.edu/faculty/burns/">radio astronomer</a> and co-investigator on NASA’s <a href="https://www.colorado.edu/ness/projects/radiowave-observations-lunar-surface-photoelectron-sheath-rolses">ROLSES program</a>, otherwise known as Radiowave Observations at the Lunar Surface of the photoElectron Sheath. ROLSES was built by the NASA Goddard Space Flight Center and is led by <a href="https://science.gsfc.nasa.gov/sci/bio/natchimuthuk.gopalswamy-1">Natchimuthuk Gopalswamy</a>. </p>
<p>The ROLSES instrument landed on the Moon as <a href="https://www.intuitivemachines.com/_files/ugd/7c27f7_51f84ee63ea744a9b7312d17fefa9606.pdf">one of six NASA payloads</a> on the Intuitive Machines lander in February. Between ROLSES and another mission scheduled for the lunar far side in two years, LuSEE-Night, our teams will land NASA’s first two radio telescopes on the Moon by 2026. </p>
<h2>Radio telescopes on the Moon</h2>
<p>The Moon – particularly the far side of the Moon – is an ideal place to do radio astronomy and study signals from extraterrestrial objects such as the Sun and the Milky Way galaxy. On Earth, the ionosphere, which <a href="https://theconversation.com/earths-magnetic-field-protects-life-on-earth-from-radiation-but-it-can-move-and-the-magnetic-poles-can-even-flip-216231">contains Earth’s magnetic field</a>, distorts and absorbs radio signals below the <a href="https://www.fcc.gov/general/fm-radio">FM band</a>. These signals might get scrambled or may not even make it to the surface of the Earth.</p>
<p>On Earth, there are also TV signals, satellite broadcasts and defense radar systems <a href="https://theconversation.com/radio-interference-from-satellites-is-threatening-astronomy-a-proposed-zone-for-testing-new-technologies-could-head-off-the-problem-199353">making noise</a>. To do higher sensitivity observations, you have to go into space, away from Earth. </p>
<p>The Moon is what scientists call <a href="https://www.sciencefocus.com/space/what-is-tidal-locking">tidally locked</a>. One side of the Moon is always facing the Earth – the “<a href="https://www.rmg.co.uk/stories/topics/what-man-moon">man in the Moon</a>” side – and the other side, <a href="https://theconversation.com/whats-on-the-far-side-of-the-moon-111306">the far side</a>, always faces away from the Earth. The Moon has no ionosphere, and with about 2,000 miles of rock between the Earth and the far side of the Moon, there’s no interference. It’s radio quiet. </p>
<p>For our first mission with ROLSES, which launched in February 2024, we will collect data about environmental conditions on the Moon near its south pole. On the Moon’s surface, <a href="https://theconversation.com/solar-storms-can-destroy-satellites-with-ease-a-space-weather-expert-explains-the-science-177510">solar wind</a> directly strikes the lunar surface and creates a charged gas, called <a href="https://www.psfc.mit.edu/vision/what_is_plasma">a plasma</a>. Electrons lift off the negatively charged surface to form a highly ionized gas. </p>
<p>This doesn’t happen on Earth because <a href="https://theconversation.com/earths-magnetic-field-protects-life-on-earth-from-radiation-but-it-can-move-and-the-magnetic-poles-can-even-flip-216231">the magnetic field deflects</a> the solar wind. But there’s no global magnetic field on the Moon. With a low frequency radio telescope like ROLSES, we’ll be able to measure that plasma for the first time, which could help scientists figure out how to keep astronauts safe on the Moon. </p>
<p>When astronauts walk around on the surface of the Moon, they’ll pick up different charges. It’s like walking across the carpet with your socks on – when you reach for a doorknob, a spark can come out of your finger. The same kind of discharge happens on the Moon from the charged gas, but it’s potentially more harmful to astronauts. </p>
<h2>Solar and exoplanet radio emissions</h2>
<p>Our team is also going to use ROLSES to look at the Sun. The Sun’s surface releases shock waves that send out highly energetic particles and low radio frequency emissions. We’ll use the radio telescopes to measure these emissions and to see bursts of low-frequency radio waves from shock waves within the solar wind.</p>
<p>We’re also going to examine the Earth from the surface of the Moon and use that process as a template for <a href="https://theconversation.com/nasas-tess-spacecraft-is-finding-hundreds-of-exoplanets-and-is-poised-to-find-thousands-more-122104">looking at radio emissions from exoplanets</a> that may harbor life <a href="https://theconversation.com/are-there-any-planets-outside-of-our-solar-system-164062">in other star systems</a>. </p>
<p>Magnetic fields are important for life because they shield the planet’s surface from the <a href="https://theconversation.com/the-scorching-winds-on-the-surface-of-the-sun-and-how-were-forecasting-them-44098">solar/stellar wind</a>. </p>
<p>In the future, our team hopes to use specialized arrays of antennas on the far side of the Moon to observe nearby stellar systems that are known to have exoplanets. If we detect the same kind of radio emissions that come from Earth, this will tell us that the planet has a magnetic field. And we can measure the strength of the magnetic field to figure out whether it’s strong enough to shield life.</p>
<h2>Cosmology on the Moon</h2>
<p>The Lunar Surface Electromagnetic Experiment at Night, or <a href="https://www.colorado.edu/ness/projects/lunar-surface-electromagnetics-experiment-night-lusee-night">LuSEE-Night</a>, will fly in early 2026 to the far side of the Moon. LuSEE-Night marks scientists’ first attempt to do cosmology on the Moon.</p>
<p>LuSEE-Night is a novel collaboration between NASA and the Department of Energy. Data will be sent back to Earth using a communications satellite in lunar orbit, <a href="https://www.esa.int/Science_Exploration/Human_and_Robotic_Exploration/A_pathway_for_communicating_at_the_Moon">Lunar Pathfinder</a>, which is funded by the European Space Agency.</p>
<p>Since the far side of the Moon is <a href="https://cosmicdawn.astro.ucla.edu/lunar_telescopes.html">uniquely radio quiet</a>, it’s the best place to do cosmological observations. During the two weeks of lunar night that happen every 14 days, there’s no emission coming from the Sun, and there’s no ionosphere. </p>
<p>We hope to study an unexplored part of the early universe called the <a href="https://www.astronomy.com/science/the-beginning-to-the-end-of-the-universe-the-cosmic-dark-ages/">dark ages</a>. The dark ages refer to before and just after the formation of the very first stars and galaxies in the universe, which is beyond what the <a href="https://webb.nasa.gov/">James Webb Space Telescope</a> can study.</p>
<p>During the dark ages, the universe was less than 100 million years old – today the universe is 13.7 billion years old. The universe was full of hydrogen <a href="https://theconversation.com/after-our-universes-cosmic-dawn-what-happened-to-all-its-original-hydrogen-65527">during the dark ages</a>. That hydrogen radiates through the universe at low radio frequencies, and when new stars turn on, they ionize the hydrogen, producing a radio signature in the spectrum. Our team hopes to measure that signal and learn about how the earliest stars and galaxies in the universe formed.</p>
<p>There’s also a lot of potential new physics that we can study in this last unexplored cosmological epoch in the universe. We will investigate the nature of <a href="https://theconversation.com/dark-matter-the-mystery-substance-physics-still-cant-identify-that-makes-up-the-majority-of-our-universe-85808">dark matter</a> and early <a href="https://theconversation.com/explainer-the-mysterious-dark-energy-that-speeds-the-universes-rate-of-expansion-40224">dark energy</a> and test our fundamental models of physics and cosmology in an unexplored age.</p>
<p>That process is going to start in 2026 with the LuSEE-Night mission, which is both a fundamental physics experiment and a cosmology experiment.</p>
<p><em>This is an updated version of an article originally published on Feb. 5, 2024.</em></p><img src="https://counter.theconversation.com/content/219892/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jack Burns receives funding from NASA.</span></em></p>Projects under NASA’s CLPS program – including the Odysseus lander that made it to the lunar surface – will probe unexplored questions about the universe’s formation.Jack Burns, Professor of Astrophysical and Planetary Sciences, University of Colorado BoulderLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2168742024-01-10T13:28:57Z2024-01-10T13:28:57ZEarth isn’t the only planet with seasons, but they can look wildly different on other worlds<figure><img src="https://images.theconversation.com/files/561980/original/file-20231127-27-h9xkjy.jpg?ixlib=rb-1.1.0&rect=0%2C6%2C2055%2C1445&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Nearby planets can affect how one planet 'wobbles' on its spin axis, which contributes to seasons. </span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/illustration/orbits-of-planets-in-the-solar-system-royalty-free-illustration/1148112202?phrase=planets+orbit&adppopup=true">Mark Garlick/Science Photo Library via Getty Images</a></span></figcaption></figure><p>Spring, summer, fall and winter – the seasons on Earth change every few months, around the same time every year. It’s easy to take this cycle for granted here on Earth, but not every planet has a regular change in seasons. So why does Earth have regular seasons when other planets don’t? </p>
<p><a href="https://scholar.google.com/citations?user=vxyrNXoAAAAJ&hl=en">I’m an astrophysicist</a> who studies the movement of planets and the causes of seasons. Throughout my research, I’ve found that Earth’s regular pattern of seasons is unique. The <a href="https://theconversation.com/how-the-earths-tilt-creates-short-cold-january-days-173403">rotational axis that Earth spins on</a>, along the North and South poles, <a href="https://en.wikipedia.org/wiki/Axial_tilt">isn’t quite aligned</a> with the vertical axis perpendicular to Earth’s orbit around the Sun. </p>
<p>That slight tilt has big implications for everything from seasons to glacier cycles. The magnitude of that tilt can even determine whether a planet is habitable to life. </p>
<h2>Seasons on Earth</h2>
<p>When a planet has perfect alignment between the axis it orbits on and the rotational axis, the amount of sunlight it receives is fixed as it orbits around the Sun – assuming its orbital shape is a circle. Since seasons come from variations in how much sunlight reaches the planet’s surface, a planet that’s perfectly aligned wouldn’t have seasons. But Earth isn’t perfectly aligned on its axis.</p>
<p>This small misalignment, called an obliquity, is <a href="https://en.wikipedia.org/wiki/Axial_tilt">around 23 degrees</a> from vertical for Earth. So, the Northern Hemisphere experiences more intense sunlight during the summer, when the Sun is positioned more directly above the Northern Hemisphere.</p>
<p>Then, as the Earth continues to orbit around the Sun, the amount of sunlight the Northern Hemisphere receives gradually decreases as the Northern Hemisphere tilts away from the Sun. This causes winter. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/566402/original/file-20231218-21-biar6k.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram showing the Earth as a blue circle on the left and on the right, with a blue arrow tilted a few degrees towards the right cutting through it, and a green arrow tilted up cutting through it. The angle between the two arrows is red, labeled 'obliquity.' In the middle is a drawing of the Sun." src="https://images.theconversation.com/files/566402/original/file-20231218-21-biar6k.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/566402/original/file-20231218-21-biar6k.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/566402/original/file-20231218-21-biar6k.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/566402/original/file-20231218-21-biar6k.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/566402/original/file-20231218-21-biar6k.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/566402/original/file-20231218-21-biar6k.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/566402/original/file-20231218-21-biar6k.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The obliquity marks the difference between the Earth’s spin axis (blue) and the vertical from orbit (green). The Northern Hemisphere experiences summer when the tilt lines it up directly with light from the Sun.</span>
<span class="attribution"><span class="source">Gongjie Li</span></span>
</figcaption>
</figure>
<p>The planets spinning on their axes and orbiting around the Sun look kind of like spinning tops – they spin around and wobble because of gravitational pull from the Sun. As a top spins, you might notice that it doesn’t just stay perfectly upright and stationary. Instead, it may start to tilt or wobble slightly. This tilt is what astrophysicists call <a href="https://www.britannica.com/science/precession-of-the-equinoxes">spin precession</a>.</p>
<p>Because of these wobbles, Earth’s obliquity isn’t perfectly fixed. These small variations in tilt can have <a href="https://www.jstor.org/stable/1746691">big effects on the Earth’s climate</a> when combined with small changes to Earth’s orbit shape. </p>
<p>The wobbling tilt and any natural variations to the shape of Earth’s orbit can change the amount and distribution of sunlight reaching Earth. These small changes contribute to the planet’s larger temperature shifts over thousands to hundreds of thousands of years. This can, in turn, <a href="https://climate.nasa.gov/news/2948/milankovitch-orbital-cycles-and-their-role-in-earths-climate/">drive ice ages and periods of warmth</a>.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/DD_8Jm5pTLk?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Earth’s seasons result from a variety of factors, including orbit and axial tilt.</span></figcaption>
</figure>
<h2>Translating obliquity into seasons</h2>
<p>So how do obliquity variations affect the seasons on a planet? Low obliquity, meaning the rotational spin axis is aligned with the planet’s orientation as it orbits around the Sun, <a href="https://climate.nasa.gov/news/2948/milankovitch-orbital-cycles-and-their-role-in-earths-climate/">leads to</a> stronger sunlight on the equator and low sunlight near the pole, like on Earth. </p>
<p>On the other hand, a high obliquity – meaning the planet’s rotational spin axis points toward or away from the Sun – <a href="https://climate.nasa.gov/news/2948/milankovitch-orbital-cycles-and-their-role-in-earths-climate/">leads to</a> extremely hot or cold poles. At the same time, the equator gets cold, as the Sun does not shine above the equator all year round. This leads to drastically varying seasons at high latitudes and low temperatures at the equator. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/566405/original/file-20231218-19-pudn6j.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A planet with a reversed zonation is represented by a blue circle next to a drawing of a sun, with a green oval representing the planet's orbit around the sun. A blue arrow pointing towards the sun represents the planet's spin axis, and a green arrow point up represents the planet's orbit direction." src="https://images.theconversation.com/files/566405/original/file-20231218-19-pudn6j.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/566405/original/file-20231218-19-pudn6j.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/566405/original/file-20231218-19-pudn6j.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/566405/original/file-20231218-19-pudn6j.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/566405/original/file-20231218-19-pudn6j.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/566405/original/file-20231218-19-pudn6j.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/566405/original/file-20231218-19-pudn6j.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">When a planet’s spin axis is tilted far from the vertical axis, it has a high obliquity. That means the equator barely gets any sunlight and the North Pole faces right at the Sun.</span>
<span class="attribution"><span class="source">Gongjie Li</span></span>
</figcaption>
</figure>
<p>When a planet has an obliquity of more than 54 degrees, that planet’s equator grows icy and <a href="https://doi.org/10.1016/0012-8252(93)90004-Q">the pole becomes warm</a>. This is called <a href="https://doi.org/10.1016/0012-8252(93)90004-Q">a reversed zonation</a>, and it’s the opposite of what Earth has. </p>
<p>Basically, if an obliquity has large and unpredictable variations, the seasonal variations on the planet become wild and hard to predict. A dramatic, large obliquity variation can turn the whole planet into a snowball, <a href="https://doi.org/10.1093/mnras/stab3179">where it’s all covered by ice</a>. </p>
<h2>Spin orbit resonances</h2>
<p>Most planets are not the only planets in their solar systems. Their planetary siblings can disturb each other’s orbit, which can lead to variations in the shape of their orbits and their orbital tilt. </p>
<p>So, planets in orbit look kind of like tops spinning on the roof of a car that’s bumping down the road, where the car represents the orbital plane. When the rate – or frequency, as scientists call it – at which the tops are precessing, or spinning, matches the frequency at which the car is bumping up and down, something called a <a href="https://doi.org/10.1038/361615a0">spin-orbit resonance</a> occurs.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/561691/original/file-20231126-23-xe830c.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram showing a planet, shown as a blue circle with an arrow through it representing a tilted, spinning axis, orbiting around the Sun, with another planet's orbit overlapping with it, causing the orbit to tilt up and down." src="https://images.theconversation.com/files/561691/original/file-20231126-23-xe830c.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/561691/original/file-20231126-23-xe830c.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/561691/original/file-20231126-23-xe830c.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/561691/original/file-20231126-23-xe830c.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/561691/original/file-20231126-23-xe830c.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/561691/original/file-20231126-23-xe830c.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/561691/original/file-20231126-23-xe830c.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The orbits of planets close by and the precession motion of a planet on its axis can affect seasonal patterns.</span>
<span class="attribution"><span class="source">Gongjie Li</span></span>
</figcaption>
</figure>
<p>Spin-orbit resonances can cause these obliquity variations, which is when a planet wobbles on its axis. Think about pushing a kid on a swing. When you push at just the right time – or at the resonant frequency – they’ll swing higher and higher.</p>
<p>Mars wobbles more on its axis than Earth does, even though the two are tilted about the same amount, and that actually has to do with the Moon orbiting around Earth. Earth and Mars have a <a href="https://doi.org/10.1038/361608a0">similar spin precession frequency</a>, which matches the orbital oscillation – the ingredients for a spin-orbit resonance. </p>
<p>But Earth has a massive Moon, which pulls on Earth’s spin axis and drives it to precess faster. This slightly faster precession prevents it from experiencing spin orbit resonances. So, the Moon stabilizes Earth’s obliquity, and Earth doesn’t wobble on its axis as much as Mars does. </p>
<h2>Exoplanet seasons</h2>
<p><a href="https://theconversation.com/are-there-any-planets-outside-of-our-solar-system-164062">Thousands of exoplanets</a>, or planets outside our solar system, have been discovered over the past few decades. My research group wanted to understand how habitable these planets are, and whether these exoplanets also have wild obliquities, or whether they have moons to stabilize them like Earth does. </p>
<p>To investigate this, my group has led the first investigation on <a href="https://doi.org/10.3847/1538-3881/aabfd1">the spin-axis variations of exoplanets</a>. </p>
<p>We investigated <a href="https://doi.org/10.3847/1538-3881/aabfd1">Kepler-186f</a>, which is the first discovered Earth-sized planet in a habitable zone. <a href="https://theconversation.com/an-earth-sized-planet-found-in-the-habitable-zone-of-a-nearby-star-129290">The habitable zone</a> is an area around a star where liquid water can exist on the surface of the planet and life may be able to emerge and thrive.</p>
<p>Unlike Earth, Kepler-186f is located far from the other planets in its solar system. As a result, these other planets have only a weak effect on its orbit and movement. So, Kepler-186f generally <a href="https://doi.org/10.3847/1538-3881/aabfd1">has a fixed obliquity</a>, similar to Earth. Even without a large moon, it doesn’t have wildly changing or unpredictable seasons like Mars.</p>
<p>Looking forward, more research into exoplanets will help scientists understand what seasons look like throughout the vast diversity of planets in the universe.</p><img src="https://counter.theconversation.com/content/216874/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Gongjie Li receives funding from NASA.</span></em></p>You might hate winter, but at least you know what to expect every year. Other planets have wobbly axes that lead to wild, unpredictable seasons.Gongjie Li, Assistant Professor of Physics, Georgia Institute of TechnologyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2191832023-12-28T19:34:18Z2023-12-28T19:34:18ZLarger and more frequent solar storms will make for potential disruptions and spectacular auroras on Earth<figure><img src="https://images.theconversation.com/files/564592/original/file-20231208-29-521tjc.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C1669%2C1669&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A sunspot emitting a flare on the surface of the sun. </span> <span class="attribution"><a class="source" href="https://images.nasa.gov/details/PIA22645">(NASA/GSFC/Solar Dynamics Observatory)</a></span></figcaption></figure><iframe style="width: 100%; height: 100px; border: none; position: relative; z-index: 1;" allowtransparency="" allow="clipboard-read; clipboard-write" src="https://narrations.ad-auris.com/widget/the-conversation-canada/larger-and-more-frequent-solar-storms-will-make-for-potential-disruptions-and-spectacular-auroras-on-earth" width="100%" height="400"></iframe>
<p>Bright auroras, with dancing lights in the sky, characterize the clear winter nights of northern Canada. Longer nights during the fall and winter also favour seeing more auroras, but the show is best outside of light-polluted cities. Impressive auroral events allowed bright auroras to be seen <a href="https://spaceweathergallery2.com/indiv_upload.php?upload_id=202170">as far south as the United States recently</a>. </p>
<p>Auroras are produced through the sun’s interaction with the Earth’s magnetic field. The number of auroras is increasing as <a href="https://www.swpc.noaa.gov/products/solar-cycle-progression">the sun’s activity becomes stronger</a>, approaching a solar maximum. </p>
<p>Perhaps surprisingly, the same space disturbances that cause auroras can affect our technologies.</p>
<p>In 1859, a geomagnetic storm — the largest in recorded history — disrupted technological systems, such as they were at the time, on Earth. Referred to as the “<a href="https://www.space.com/the-carrington-event">Carrington Event</a>” after Richard Carrington, the amateur astronomer who made the connection between a bright solar flare and subsequent auroral and magnetic effects. </p>
<p>That Sun-Earth link was slow to be accepted, but we now know that the Sun can trigger disturbances in near-Earth space, although it seems that events as large as that of 1859 are rare. </p>
<h2>Night visions</h2>
<p>Space is filled with thin hot gas called plasma that <a href="https://svs.gsfc.nasa.gov/14299/">carries magnetic fields</a>. The Earth, in the sun’s outer atmosphere, is surrounded by hot magnetic plasma which rushes past us at speeds of several hundred kilometres per second <a href="https://www.nasa.gov/solar-system/parker-solar-probe-and-the-birth-of-the-solar-wind/">in a flow called the solar wind</a>.</p>
<p>The sun is so massive that loss of the solar wind has a negligible effect on it, but Earth by comparison is a mere speck, three parts in a million as massive. <a href="https://www.nasa.gov/image-article/earths-magnetosphere-3/">Earth has a magnetic field</a>, which protects us from the solar onslaught, but is pushed back by it as well.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/564595/original/file-20231209-17-dta2j1.gif?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="a blue ball of light" src="https://images.theconversation.com/files/564595/original/file-20231209-17-dta2j1.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/564595/original/file-20231209-17-dta2j1.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/564595/original/file-20231209-17-dta2j1.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/564595/original/file-20231209-17-dta2j1.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/564595/original/file-20231209-17-dta2j1.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/564595/original/file-20231209-17-dta2j1.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/564595/original/file-20231209-17-dta2j1.gif?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">These active regions may dramatically flare up in X-ray intensity, affecting Earth’s upper atmosphere and making a hazard for astronauts.</span>
<span class="attribution"><span class="source">(Solar Dynamics Observatory/NASA)</span></span>
</figcaption>
</figure>
<p>Under certain conditions, energy can flow into the near-Earth region from the solar wind, largely building up on the opposite side from the sun in a comet-like “<a href="https://www.jstor.org/stable/24975910">magnetotail</a>.”</p>
<p>This can become unstable if too much energy builds up, blasting particles into the nightside atmosphere to light up auroras. This explains why auroras are seen at night: not only is it dark, but the sun’s energy takes an indirect route by first being stored in the magnetotail.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/o4FSg-90XlA?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">A NASA video explaining the magnetosphere.</span></figcaption>
</figure>
<p>The dancing auroras can also generate magnetic fields, which are strong enough to be detected by a compass, as discovered nearly 300 years ago by <a href="https://www.britannica.com/biography/Anders-Celsius">Swedish astronomer Anders Celsius</a>.</p>
<p>If the magnetic fields change rapidly, they can affect large regions of the Earth, building up to cause problems for power networks. This notably happened in North America in 1989, on the “<a href="https://spaceweatherarchive.com/2021/03/12/the-great-quebec-blackout">day the sun brought darkness</a>.”</p>
<h2>Solar cycles</h2>
<p>Italian astronomer Galileo studied sunspots in a systematic way in <a href="http://galileo.rice.edu/sci/observations/sunspots.html">the early 1600s</a>. About 300 years later, American astronomer George Hale showed that sunspots had intense magnetic fields, <a href="https://www2.hao.ucar.edu/education/scientists/george-ellery-hale-1868-1938">several thousand times stronger than Earth’s</a>. </p>
<p>In the 400 years since Galileo’s observations, we have found that the number of sunspots varies dramatically over <a href="https://www.swpc.noaa.gov/phenomena/sunspotssolar-cycle">an 11-year long cycle</a>. But it is only recently, in the Space Age, that we can relate its effects on Earth.</p>
<h2>Energy storage</h2>
<p>Magnetic fields store energy, and sometimes, as in Earth’s magnetotail or near sunspots, this energy can be changed to other forms. In the strong fields of sunspots, it can be released as X-rays in <a href="https://www.youtube.com/watch?v=64CTIrWBGTc">rapid, unpredictable flares</a>. </p>
<p>Sunspots and flares are near the surface or light-emitting layer of the sun, but <a href="https://www.swpc.noaa.gov/news/strongest-solar-flare-solar-cycle-25">material can escape from the sun’s strong gravity field</a>. Blobs of gas — <a href="https://www.swpc.noaa.gov/phenomena/coronal-mass-ejections">coronal mass ejections</a> — can be hurtled into space. Some small fraction of these are shot out toward Earth, and auroras and their magnetic effects occur when they reach Earth’s atmosphere. They can also cause intensification of our radiation belts in ways that <a href="https://doi.org/10.1511/2014.110.374">can damage satellites</a>.</p>
<p>Counting sunspots on the sun’s surface allows us to get a general idea of what space disturbances may occur as the solar cycle progresses. Similarly, on Earth we can follow the seasons and have a general idea of what storms are likely. In both cases, however, exact prediction is difficult.</p>
<h2>Space weather forecasts</h2>
<p>From long-term trends, it was expected that the upcoming solar maximum would be small, as indeed <a href="https://doi.org/10.1051/swsc/2020060">the one that peaked in 2014 was</a>. However, in this, <a href="https://www.nasa.gov/news-release/solar-cycle-25-is-here-nasa-noaa-scientists-explain-what-that-means/">the following solar cycle</a>, we have already exceeded predicted numbers of sunspots and had large magnetic storms, so predictions may need to be revised upward. </p>
<p>Although direct measurement of incoming disturbances by satellites in the solar wind gives us only about an hour’s warning of stormy space weather, we can also predict a bit further in advance by watching sunspots rotate into view as the sun turns. </p>
<p>One solar rotation takes about as long as it does for the moon to go around Earth, that is to say, a month. So if a particular sunspot brings lots of activity, it likely will repeat in about a month.</p>
<h2>Rare storms</h2>
<p>The strongest flare of <a href="https://www.swpc.noaa.gov/news/sunspot-region-produces-x28-flare-largest-sep-10-2017">Solar Cycle 25 so far occurred on Dec. 14</a>, and was the most powerful eruption the sun has produced <a href="https://www.nasa.gov/missions/goes/september-2017s-intense-solar-activity-viewed-from-space">since the great storms of September 2017</a>.</p>
<p>Large solar storms are rare, but we must calmly prepare for possible space weather impacts that should maximize in a few years. We must be creative, since space weather effects can bring surprises. In 2022, unexpected heating of the atmosphere caused <a href="https://www.space.com/spacex-starlink-satellite-loss-space-weather-forecast">multiple satellite losses</a>. </p>
<p>As our knowledge of space physics steadily improves, so too will the new science of space weather prediction, allowing us to protect our technological assets. </p>
<p>In the meantime, we can look forward to spectacular auroras that should come as we near the 2025 solar maximum, with only measured and reasonable amounts of worry about the potential impacts of space weather.</p><img src="https://counter.theconversation.com/content/219183/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Martin Gerard Connors receives funding from Canada's NSERC. </span></em></p>The sun is expected to reach its solar maximum in 2025. Recent auroras suggest that the maximum may be bigger than predicted.Martin Connors, Professor of Space Science and Physics, Athabasca UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2158932023-12-24T20:53:47Z2023-12-24T20:53:47ZA short history of sunscreen, from basting like a chook to preventing skin cancer<p>Australians have used commercial creams, lotions or gels to manage our skin’s sun exposure for nearly a century. </p>
<p>But why we do it, the preparations themselves, and whether they work, has changed over time.</p>
<p>In this short history of sunscreen in Australia, we look at how we’ve slathered, slopped and spritzed our skin for sometimes surprising reasons.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/4-myths-about-sunscreen-and-why-theyre-wrong-125879">4½ myths about sunscreen and why they're wrong</a>
</strong>
</em>
</p>
<hr>
<h2>At first, suncreams helped you ‘tan with ease’</h2>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/562563/original/file-20231129-23-98jddw.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Advertisement for Hamilton's Sunburn Vanishing Cream" src="https://images.theconversation.com/files/562563/original/file-20231129-23-98jddw.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/562563/original/file-20231129-23-98jddw.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=1129&fit=crop&dpr=1 600w, https://images.theconversation.com/files/562563/original/file-20231129-23-98jddw.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=1129&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/562563/original/file-20231129-23-98jddw.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=1129&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/562563/original/file-20231129-23-98jddw.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1418&fit=crop&dpr=1 754w, https://images.theconversation.com/files/562563/original/file-20231129-23-98jddw.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1418&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/562563/original/file-20231129-23-98jddw.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1418&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">This early sunscreen claimed you could ‘tan with ease’.</span>
<span class="attribution"><a class="source" href="https://trove.nla.gov.au/newspaper/page/11041390?searchTerm=Hamilton%20sun%20vanishing%20cream">Trove/NLA</a></span>
</figcaption>
</figure>
<p>Sunscreens have been available in Australia since the 30s. Chemist <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10120514/">Milton Blake</a> made one of the first.</p>
<p>He used a kerosene heater to cook batches of “sunburn vanishing cream”, scented with French perfume. </p>
<p>His backyard business became H.A. Milton (Hamilton) Laboratories, which still <a href="https://www.hamiltonsunandskin.com.au/history-of-hamilton">makes sunscreens today</a>. </p>
<p>Hamilton’s first cream <a href="https://trove.nla.gov.au/newspaper/article/128464119?searchTerm=Hamilton%20sun%20vanishing%20cream">claimed</a> you could “
Sunbathe in Comfort and TAN with ease”. According to modern standards, it would have had an SPF (or sun protection factor) of 2.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/explainer-how-does-sunscreen-work-what-is-spf-and-can-i-still-tan-with-it-on-88869">Explainer: how does sunscreen work, what is SPF and can I still tan with it on?</a>
</strong>
</em>
</p>
<hr>
<h2>The mirage of ‘safe tanning’</h2>
<p>A tan was considered a “<a href="https://trove.nla.gov.au/newspaper/article/21611069?searchTerm=sunburn%20lotion">modern complexion</a>” and for most of the 20th century, you might put something on your skin to help gain one. That’s when “safe tanning” (without burning) was thought possible.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/562843/original/file-20231130-27-l79asi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Coppertone advertisement showing tanned woman in bikini" src="https://images.theconversation.com/files/562843/original/file-20231130-27-l79asi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/562843/original/file-20231130-27-l79asi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=862&fit=crop&dpr=1 600w, https://images.theconversation.com/files/562843/original/file-20231130-27-l79asi.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=862&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/562843/original/file-20231130-27-l79asi.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=862&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/562843/original/file-20231130-27-l79asi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1083&fit=crop&dpr=1 754w, https://images.theconversation.com/files/562843/original/file-20231130-27-l79asi.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1083&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/562843/original/file-20231130-27-l79asi.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1083&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">This 1967 Coppertone advertisement urged you to ‘tan, not burn’.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/91591049@N00/15224409766/in/photolist-pck5By-nY3gWR-86iQ6o">SenseiAlan/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Sunburn was known to be caused by the <a href="https://www.cancercouncil.com.au/cancer-prevention/sun-protection/understanding-uv-radiation/what-is-uv-radiation/">UVB component</a> of ultraviolet (UV) light. UVA, however, was thought not to be involved in burning; it was just thought to darken the skin pigment melanin. So, medical authorities advised that by using a sunscreen that filtered out UVB, you could “safely tan” without burning.</p>
<p>But that was wrong.</p>
<p>From the 70s, medical research suggested UVA <a href="https://onlinelibrary.wiley.com/doi/full/10.1111/exd.12388">penetrated damagingly deep</a> into the skin, causing ageing effects such as sunspots and wrinkles. And both <a href="https://www.cancercouncil.com.au/cancer-prevention/sun-protection/understanding-uv-radiation/what-is-uv-radiation/">UVA and UVB</a> could cause skin cancer.</p>
<p>Sunscreens from the 80s sought to be “<a href="https://theconversation.com/how-to-pick-the-right-sunscreen-when-youre-blinded-by-choice-125881">broad spectrum</a>” – they filtered both UVB and UVA.</p>
<p>Researchers consequently recommended sunscreens for <a href="https://www.sbs.com.au/language/english/en/article/skin-cancer-in-australia-what-are-the-risks-and-how-to-protect-yourself/sa022ydq1">all skin tones</a>, including for preventing sun damage in people with <a href="https://www.skincancer.org/skin-cancer-information/skin-cancer-skin-of-color/">dark skin</a>.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/sun-damage-and-cancer-how-uv-radiation-affects-our-skin-34538">Sun damage and cancer: how UV radiation affects our skin</a>
</strong>
</em>
</p>
<hr>
<h2>Delaying burning … or encouraging it?</h2>
<p>Up to the 80s, sun preparations ranged from something that claimed to delay burning, to preparations that actively encouraged it to get that desirable tan – think, baby oil or coconut oil. Sun-worshippers even raided the kitchen cabinet, slicking olive oil on their skin.</p>
<p>One manufacturer’s “sun lotion” might effectively filter UVB; another’s merely basted you like a roast chicken.</p>
<p>Since labelling laws before the 80s didn’t require manufacturers to list the ingredients, it was often hard for consumers to tell which was which.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/how-should-i-add-sunscreen-to-my-skincare-routine-now-its-getting-hotter-213453">How should I add sunscreen to my skincare routine now it's getting hotter?</a>
</strong>
</em>
</p>
<hr>
<h2>At last, SPF arrives to guide consumers</h2>
<p>In the 70s, two Queensland researchers, Gordon Groves and Don Robertson, developed tests for sunscreens – sometimes experimenting on students or colleagues. They printed their ranking <a href="https://trove.nla.gov.au/newspaper/article/116399802?searchTerm=guide%20to%20sunburn%20protection">in the newspaper</a>, which the public could use to choose a product. </p>
<p>An Australian sunscreen manufacturer then asked the federal health department to regulate the industry. The company wanted standard definitions to market their products, backed up by consistent lab testing methods.</p>
<p><a href="https://store.standards.org.au/product/as-2604-1986">In 1986</a>, after years of consultation with manufacturers, researchers and consumers, Australian Standard AS2604 gave a specified a testing method, based on the Queensland researchers’ work. We also had a way of expressing how well sunscreens worked – the <a href="https://theconversation.com/explainer-how-does-sunscreen-work-what-is-spf-and-can-i-still-tan-with-it-on-88869">sun protection factor or SPF</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/562856/original/file-20231130-17-70ggq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Sunscreen products with various SPF labels" src="https://images.theconversation.com/files/562856/original/file-20231130-17-70ggq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/562856/original/file-20231130-17-70ggq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=257&fit=crop&dpr=1 600w, https://images.theconversation.com/files/562856/original/file-20231130-17-70ggq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=257&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/562856/original/file-20231130-17-70ggq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=257&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/562856/original/file-20231130-17-70ggq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=323&fit=crop&dpr=1 754w, https://images.theconversation.com/files/562856/original/file-20231130-17-70ggq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=323&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/562856/original/file-20231130-17-70ggq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=323&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Consumers could pick their product based on the sun protection factor or SPF.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-vector/set-sunscreen-products-on-turquoise-background-2291735329">Shutterstock</a></span>
</figcaption>
</figure>
<p>This is the ratio of how long it takes a fair-skinned person to burn using the product compared with how long it takes to burn without it. So a cream that protects the skin sufficiently so it takes 40 minutes to burn instead of 20 minutes has an SPF of 2.</p>
<p>Manufacturers liked SPF because businesses that invested in clever chemistry could distinguish themselves in marketing. Consumers liked SPF because it was easy to understand – the higher the number, the better the protection.</p>
<p>Australians, encouraged from 1981 by the <a href="https://www.youtube.com/watch?v=b7nocIenCYg%22">Slip! Slop! Slap!</a> nationwide skin cancer campaign, could now “slop” on a sunscreen knowing the degree of protection it offered.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/how-to-pick-the-right-sunscreen-when-youre-blinded-by-choice-125881">How to pick the right sunscreen when you're blinded by choice</a>
</strong>
</em>
</p>
<hr>
<h2>How about skin cancer?</h2>
<p>It wasn’t until 1999 that research proved that using sunscreen prevents skin cancer. Again, we have Queensland to thank, specifically the residents of Nambour. They took part in a <a href="https://pubmed.ncbi.nlm.nih.gov/10475183/">trial</a> for nearly five years, carried out by a research team led by Adele Green of the Queensland Institute of Medical Research. Using sunscreen daily over that time reduced rates of squamous cell carcinoma (a common form of skin cancer) by about 60%.</p>
<p>Follow-up <a href="https://pubmed.ncbi.nlm.nih.gov/21135266/">studies</a> in 2011 and 2013 showed regular sunscreen use almost halved the rate of melanoma and <a href="https://pubmed.ncbi.nlm.nih.gov/23732711/">slowed skin ageing</a>. But there was no impact on rates of <a href="https://www.cancer.org.au/cancer-information/types-of-cancer/non-melanoma-skin-cancer">basal cell carcinoma</a>, another common skin cancer. </p>
<p>By then, researchers had shown sunscreen stopped sunburn, and stopping sunburn would prevent at least some types of skin cancer.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1729258841827635600"}"></div></p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/theres-a-serious-ethical-problem-with-some-sunscreen-testing-methods-and-youre-probably-not-aware-of-it-195359">There's a serious ethical problem with some sunscreen testing methods – and you're probably not aware of it</a>
</strong>
</em>
</p>
<hr>
<h2>What’s in sunscreen today?</h2>
<p>An effective sunscreen uses one or more active ingredients in a cream, lotion or gel. The <a href="https://theconversation.com/explainer-how-does-sunscreen-work-what-is-spf-and-can-i-still-tan-with-it-on-88869">active ingredient</a> either works:</p>
<ul>
<li><p>“chemically” by absorbing UV and converting it to heat. Examples include PABA (para-aminobenzoic acid) and benzyl salicylate, or</p></li>
<li><p>“physically” by blocking the UV, such as zinc oxide or titanium dioxide. </p></li>
</ul>
<p>Physical blockers at first had limited cosmetic appeal because they were opaque pastes. (Think cricketers with zinc smeared on their noses.) </p>
<p>With microfine particle technology from the 90s, sunscreen manufacturers could then use a combination of chemical absorbers and physical blockers to achieve high degrees of sun protection in a cosmetically acceptable formulation.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/research-check-should-we-be-worried-that-the-chemicals-from-sunscreen-can-get-into-our-blood-116738">Research Check: should we be worried that the chemicals from sunscreen can get into our blood?</a>
</strong>
</em>
</p>
<hr>
<h2>Where now?</h2>
<p>Australians have embraced sunscreen, but they still don’t apply enough <a href="https://www.cancervic.org.au/get-support/stories/australians-dont-apply-enough-sunscreen.html">or</a> reapply often enough.</p>
<p>Although some people are concerned sunscreen will block the skin’s ability to <a href="https://theconversation.com/should-i-be-getting-my-vitamin-d-levels-checked-211268">make vitamin D</a> this is unlikely. That’s because even SPF50 sunscreen doesn’t filter out all UVB.</p>
<p>There’s also concern about the active ingredients in sunscreen <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9652235/">getting into the environment</a> and whether their <a href="https://www.fda.gov/drugs/news-events-human-drugs/spotlight-cder-science-new-fda-study-shines-light-sunscreen-absorption">absorption by our bodies</a> is a problem.</p>
<p>Sunscreens have evolved from something that at best offered mild protection to effective, easy-to-use products that stave off the harmful effects of UV. They’ve evolved from something only people with fair skin used to a product for anyone.</p>
<p>Remember, slopping on sunscreen is just one part of sun protection. Don’t forget to also slip (protective clothing), slap (hat), seek (shade) and slide (sunglasses).</p><img src="https://counter.theconversation.com/content/215893/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Laura Dawes does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Early products focused on tanning. Others roasted you like a chicken. Which of these claims can you remember?Laura Dawes, Research Fellow in Medico-Legal History, Australian National UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2186702023-12-06T15:53:47Z2023-12-06T15:53:47ZWhy dimming the Sun would be an effective tool in the fight against climate change<p>It’s becoming increasingly clear that we will fail to meet our climate goals. We were already at <a href="https://www.nature.com/articles/d41586-023-03775-z">1.26°C</a> of warming in 2022 and are on track to blow through <a href="https://cds.climate.copernicus.eu/apps/c3s/app-c3s-global-temperature-trend-monitor?month:float=10&year:float=2023">1.5°C in the mid-2030s</a>. Research even suggests that current climate policy will lead to <a href="https://climateactiontracker.org/global/cat-thermometer/">more than 2.5°C</a> of warming by the end of this century. </p>
<p>Warming of this magnitude would devastate vulnerable communities and ecosystems around the world. It’s time we consider something radically new that could stop climate change in its tracks.</p>
<p>After powerful volcanic eruptions, like Tambora (Indonesia) in 1815 and Pinatubo (Philippines) in 1991, <a href="https://scied.ucar.edu/learning-zone/how-climate-works/how-volcanoes-influence-climate#:%7E:text=Volcanic%20ash%20or%20dust%20released,cools%20the%20area%20directly%20below.">global temperatures dip</a> for a few years. Major eruptions create a hazy layer of microscopic particles in the upper atmosphere that last for several years, dimming the Sun temporarily. We could copy this effect to fight climate change.</p>
<p>The Earth is warmed by the Sun, but it is <a href="https://www.nasa.gov/centers-and-facilities/langley/what-is-earths-energy-budget-five-questions-with-a-guy-who-knows/#:%7E:text=Earth's%20energy%20budget%3F-,Earth's%20energy%20budget%20describes%20the%20balance%20between%20the%20radiant%20energy,portion%20of%20the%20electromagnetic%20spectrum.">kept warm by greenhouse gases</a> that trap the heat our planet gives off. The warming effect of our CO₂ emissions could be countered by creating a persistent, artificial haze like those seen following major volcanic eruptions. Research has found that we would only need to dim the Sun <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/jgrd.50646">by around 1%</a> to cool the planet by 1°C. </p>
<p>This may sound unlikely. But every engineering assessment to date has concluded that it would be <a href="https://iopscience.iop.org/article/10.1088/1748-9326/aba7e7/meta">feasible and relatively cheap</a> to do using a fleet of high-flying jets to release reflective particles into the upper atmosphere. </p>
<p>So we could dim the Sun – but should we?</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/563617/original/file-20231205-23-pz9rq2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Ash cloud of Pinatubo during the 1991 eruption." src="https://images.theconversation.com/files/563617/original/file-20231205-23-pz9rq2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/563617/original/file-20231205-23-pz9rq2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=402&fit=crop&dpr=1 600w, https://images.theconversation.com/files/563617/original/file-20231205-23-pz9rq2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=402&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/563617/original/file-20231205-23-pz9rq2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=402&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/563617/original/file-20231205-23-pz9rq2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=505&fit=crop&dpr=1 754w, https://images.theconversation.com/files/563617/original/file-20231205-23-pz9rq2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=505&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/563617/original/file-20231205-23-pz9rq2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=505&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Ash cloud of Pinatubo during the 1991 eruption.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Pinatubo_ash_plume_910612.jpg">Dave Harlow / US Geological Survey</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-sa/4.0/">CC BY-NC-SA</a></span>
</figcaption>
</figure>
<h2>Cooling the planet would work</h2>
<p>Dimming the Sun wouldn’t perfectly reverse climate change. The Sun’s warming effect is strongest during the day, in the summer and at the Tropics, whereas greenhouse gases warm everywhere and at all times. </p>
<p>However, we could create <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019JD030329">an even cooling effect</a> across the world by adjusting where we release the particles. Research suggests that such an approach would <a href="https://royalsocietypublishing.org/doi/full/10.1098/rsta.2016.0454">greatly reduce climate risks</a>. </p>
<p>Rising temperatures really matter. Species around the world are <a href="https://www.science.org/doi/full/10.1126/science.aai9214?casa_token=2qPuH36buhAAAAAA%3AJM9WQcq2tEqIVUDc6yqWP5AOcXOzenwYhY9BCkZAE37QXjk-ndpn-JcqLzjjIxQmAuF88r9G0f2plA">on the move</a>, tracking familiar temperatures polewards as the planet warms up. But many won’t be able to keep pace with the changing climate and others have nowhere to go, so extinctions are <a href="https://www.science.org/doi/10.1126/science.aaa4984">projected to increase</a>. </p>
<p>We are also seeing extreme heat that is edging closer to the <a href="https://www.pnas.org/doi/10.1073/pnas.2316003120">absolute limits of the human body</a>, putting lives at risk and limiting outdoor work.</p>
<p>As the planet heats up, warmer air is drawing more moisture from the soil in dry times, and dumping more out at once when it rains. This is making dry regions drier, wet regions wetter, and is <a href="https://www.nature.com/articles/s44221-023-00047-y">intensifying both droughts and floods</a> across the world. </p>
<p>Dimming the Sun would offset this effect. But it would still alter global wind and rainfall patterns. </p>
<p>Research indicates that this would mean smaller rainfall changes overall. However, <a href="https://www.nature.com/articles/s41558-019-0398-8">a small minority of places</a> could see more pronounced changes in rainfall compared to what they would face under climate change. Climate models disagree on the details of regional rainfall changes, so it’s unclear at this stage which regions would see the greatest change. </p>
<p>Blocking some sunlight <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2023EF003679">would also be an effective</a> way of keeping icy parts of the world frozen. Rising temperatures are causing the Antarctic and Greenland ice sheets to melt at an accelerating rate, <a href="https://www.climate.gov/news-features/understanding-climate/climate-change-global-sea-level">driving up the global sea level</a>. Climate change is also thawing permafrost (frozen soil that stores vast amounts of carbon) leading to the <a href="https://www.nature.com/articles/s43017-021-00230-3">emission of more</a> of methane and CO₂. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/563619/original/file-20231205-22-4p9vrw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Broken pieces of Arctic sea ice." src="https://images.theconversation.com/files/563619/original/file-20231205-22-4p9vrw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/563619/original/file-20231205-22-4p9vrw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=398&fit=crop&dpr=1 600w, https://images.theconversation.com/files/563619/original/file-20231205-22-4p9vrw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=398&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/563619/original/file-20231205-22-4p9vrw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=398&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/563619/original/file-20231205-22-4p9vrw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/563619/original/file-20231205-22-4p9vrw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/563619/original/file-20231205-22-4p9vrw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=501&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Melting ice can accelerate the pace of global warming.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/usgeologicalsurvey/4370267907/in/set-72157623467470824">US Geological Survey</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-sa/4.0/">CC BY-NC-SA</a></span>
</figcaption>
</figure>
<h2>Side effects</h2>
<p>Although dimming the Sun could keep the Earth cool, it would not deal with the root of the climate problem: the buildup of CO₂ and other greenhouse gases in the atmosphere. CO₂ not only warms the planet, it also <a href="https://oceanservice.noaa.gov/facts/acidification.html#:%7E:text=Ocean%20acidification%20refers%20to%20a,CO2%20from%20the%20atmosphere.">acidifies the ocean</a>, making it harder for corals and other creatures to form their shells. Dimming the Sun wouldn’t change this.</p>
<p>It would bring about some side effects as well. This hazy layer of particles would make the sky <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2012GL051652">a little whiter</a>. And if we copy volcanic eruptions by releasing sulphate particles to the upper atmosphere, then we’d also be adding to <a href="https://www.epa.gov/acidrain/what-acid-rain#:%7E:text=Acid%20rain%20results%20when%20sulfur,form%20sulfuric%20and%20nitric%20acids.">the acid rain problem</a>. </p>
<p>These particles could impact <a href="https://www.eea.europa.eu/en/topics/in-depth/climate-change-mitigation-reducing-emissions/current-state-of-the-ozone-layer">the ozone layer</a> too, which protects us from harmful UV rays. Research suggests that adding more sulphate particles to the upper atmosphere would <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2021GL094058">delay the slow recovery</a> of the ozone hole.</p>
<p>These side effects are a concern. But they pale in comparison to the impacts of climate change. A <a href="https://media.rff.org/documents/WP_23-23.pdf">recent study</a> found that the benefit of reduced extreme heat for human health could outweigh the health impacts of these side-effects by more than 50 to 1.</p>
<p>Paul Crutzen, who <a href="https://www.nobelprize.org/prizes/chemistry/1995/crutzen/facts/">won a Nobel prize</a> in 1995 for solving the chemistry of the ozone hole, was well aware of these side effects but nevertheless argued that we should start taking the idea of dimming the Sun seriously. In an article from 2006, <a href="https://www.proquest.com/docview/198512444?pq-origsite=gscholar&fromopenview=true">he stressed</a> that it would be best to cut CO₂ emissions rapidly so that we wouldn’t need to consider dimming the Sun at all. However, <a href="https://www.independent.co.uk/climate-change/news/scientist-publishes-escape-route-from-global-warming-409981.html">he lamented</a> that “currently, this looks like a pious wish”.</p>
<h2>Symptoms matter</h2>
<p>It’s becoming increasingly clear that this “pious wish” isn’t coming true. Since Crutzen’s 2006 article, <a href="https://essd.copernicus.org/articles/14/4811/2022/">CO₂ emissions</a> have surged by more than 15%. We just aren’t cutting emissions fast enough to prevent climate change from wreaking terrible damage. </p>
<p>Dimming the Sun would not address the root cause of the climate disease, and we must keep pushing to cut emissions, but a growing body of evidence suggests that it would work surprisingly well at treating the symptoms.</p>
<p>However, this is not so surprising. Ice melts when it is warm, hotter air carries more moisture and heat has a direct impact on life. We are far from knowing enough to recommend dimming the Sun today, but if countries don’t start taking this idea seriously we may miss a valuable opportunity to reduce the risks of climate change.</p>
<hr>
<figure class="align-right ">
<img alt="Imagine weekly climate newsletter" src="https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
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</figcaption>
</figure>
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<p class="fine-print"><em><span>Peter Irvine receives funding from Horizon Europe. He acts as a scientific advisor to the Degrees Initiative, an NGO which funds developing world research into solar radiation modification geoengineering. </span></em></p>Releasing reflective particles into the upper atmosphere would help us tackle climate change – but it’s not without risk.Peter Irvine, Lecturer in Earth Sciences, UCLLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2178612023-11-30T19:06:13Z2023-11-30T19:06:13ZMassive planet too big for its own sun pushes astronomers to rethink exoplanet formation<figure><img src="https://images.theconversation.com/files/562186/original/file-20231128-23-oz4tck.jpg?ixlib=rb-1.1.0&rect=0%2C8%2C1997%2C1488&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">LHS 3154b, a newly discovered massive planet that should be too big to exist. </span> <span class="attribution"><span class="source">The Pennsylvania State University</span></span></figcaption></figure><p>Imagine you’re a farmer searching for eggs in the chicken coop – but instead of a chicken egg, you find an ostrich egg, much larger than anything a chicken could lay.</p>
<p>That’s a little how <a href="https://scholar.google.com/citations?user=cSnTlM4AAAAJ&hl=en">our team</a> <a href="https://scholar.google.com/citations?user=lN5yvjMAAAAJ&hl=en">of astronomers</a> <a href="https://science.psu.edu/astrp/people/mmd6393">felt when we</a> <a href="https://doi.org/10.1126/science.abo0233">discovered a massive planet</a>, more than 13 times heavier than Earth, around a cool, dim red star, nine times less massive than Earth’s Sun, in 2023. </p>
<p>The smaller star, called an M star, is not only smaller than the Sun in Earth’s solar system, but it’s 100 times less luminous. Such a star should not have the necessary amount of material in its planet-forming disk to birth such a massive planet.</p>
<h2>The Habitable Zone Planet Finder</h2>
<p>Over the past decade, our team designed and built a new instrument at Penn State capable of detecting the light from these dim, cool stars at wavelengths beyond the sensitivity of the human eye – in the near-infrared – where such cool stars <a href="https://www.e-education.psu.edu/astro801/book/export/html/1755">emit most of their light</a>. </p>
<p>Attached to the 10-meter Hobby-Eberly Telescope in West Texas, our instrument, dubbed the <a href="https://hpf.psu.edu/">Habitable Zone Planet Finder</a>, can measure the subtle change in a star’s velocity as a planet gravitationally tugs on it. This technique, called the Doppler radial velocity technique, is <a href="https://theconversation.com/rarity-of-jupiter-like-planets-means-planetary-systems-exactly-like-ours-may-be-scarce-52116">great for detecting exoplanets</a>. </p>
<p>“<a href="https://exoplanets.nasa.gov/">Exoplanet</a>” is a combination of the words extrasolar and planet, so the term applies to any planet-sized body in orbit around a star that isn’t Earth’s Sun.</p>
<p>Thirty years ago, Doppler radial velocity observations enabled the discovery of <a href="https://exoplanets.nasa.gov/exoplanet-catalog/7001/51-pegasi-b/">51 Pegasi b</a>, the first known exoplanet orbiting a Sunlike star. In the ensuing decades, astronomers like us have improved this technique. These <a href="https://noirlab.edu/public/projects/neid/">increasingly more precise</a> measurements have an important goal: to enable the discovery of rocky planets in <a href="https://exoplanets.nasa.gov/search-for-life/habitable-zone/">habitable zones</a>, the regions around stars where liquid water can be sustained on the planetary surface. </p>
<p>The Doppler technique doesn’t yet have the capabilities to discover habitable zone planets the mass of the Earth around stars the size of the Sun. But the cool and dim M stars show a larger Doppler signature for the same Earth-size planet. The lower mass of the star leads to it getting tugged more by the orbiting planet. And the lower luminosity leads to a <a href="https://exoplanets.nasa.gov/resources/2255/what-is-the-habitable-zone/">closer-in habitable zone</a> and a shorter orbit, which also makes the planet easier to detect. </p>
<p>Planets around these smaller stars were the planets our team designed the Habitable Zone Planet Finder to discover. Our new discovery, <a href="https://doi.org/10.1126/science.abo0233">published in the journal Science</a>, of a massive planet orbiting closely around the cool dim M star LHS 3154 – the ostrich egg in the chicken coop – came as a real surprise.</p>
<h2>LHS 3154b: The planet that should not exist</h2>
<p><a href="https://theconversation.com/astronomers-have-learned-lots-about-the-universe-but-how-do-they-study-astronomical-objects-too-distant-to-visit-214320">Planets form in disks</a> composed of gas and dust. These disks pull together dust grains that grow into pebbles and eventually combine to form a solid planetary core. Once the core is formed, the planet can gravitationally pull in the solid dust, as well as surrounding gas such as hydrogen and helium. But it needs a lot of mass and materials to do this successfully. This way to form planets is called <a href="https://earthhow.com/planet-formation/">core accretion</a>.</p>
<p>A star as low mass as LHS 3154, nine times less massive than the Sun, should have a correspondingly low-mass planet forming disk. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/eSdZR4zT_UM?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">An artist’s rendering of LHS 3154b. Video Credit: Abby Minnich.</span></figcaption>
</figure>
<p>A typical disk around such a low-mass star should simply not have enough solid materials or mass to be able to make a core heavy enough to create such a planet. From computer simulations our team conducted, we concluded that such a planet needs a disk at least 10 times more massive than typically assumed <a href="https://doi.org/10.48550/arXiv.1608.03621">from direct observations of planet-forming disks</a>.</p>
<p>A different planet formation theory, <a href="https://astrobites.org/2011/02/28/planet-formation-at-wide-orbits-through-gravitational-instability/">gravitational instability</a> – where gas and dust in the disk undergo a direct collapse to form a planet – also struggles to explain the formation of such a planet without a very massive disk.</p>
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<h2>Planets around the most common stars</h2>
<p>Cool, dim M stars are <a href="https://www.stsci.edu/contents/newsletters/2020-volume-37-issue-01/how-well-do-we-understand-m-dwarfs">the most common stars in our galaxy</a>. In DC comics lore, <a href="https://theconversation.com/how-astronomers-could-find-the-real-planet-krypton-56646">Superman’s home world</a>, <a href="https://www.theguardian.com/culture/us-news-blog/2012/nov/05/neil-degrasse-tyson-superman-planet">planet Krypton, orbited an M dwarf star</a>. </p>
<p>Astronomers know, from discoveries made with Habitable Zone Planet Finder and other instruments, that giant planets in close-in orbits around the most massive M stars are <a href="https://doi.org/10.48550/arXiv.2303.00659">at least 10 times rarer</a> than those around Sunlike stars. And we know of no such massive planets in close orbits around the least massive M stars – until the discovery of LHS 3154b. </p>
<p>Understanding how planets form around our coolest neighbors will help us understand both how planets form in general and how rocky worlds around the most numerous types of stars form and evolve. This line of research could also help astronomers understand whether M stars are capable of supporting life.</p><img src="https://counter.theconversation.com/content/217861/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Suvrath Mahadevan receives external funding from NSF, NASA, and the Heising-Simons Foundation, as well as research funding and support from Penn State.
</span></em></p><p class="fine-print"><em><span>Guðmundur Kári Stefánsson receives funding from NSF, NASA and the Heising-Simons Foundation.</span></em></p><p class="fine-print"><em><span>Megan Delamer receives funding from NSF, NASA, and Heising-Simons Foundation. </span></em></p>A newly discovered planet that should be too big to have formed around a tiny star is throwing into question what researchers know about planet formation.Suvrath Mahadevan, Verne M. Willaman Professor of Astronomy & Astrophysics, Penn StateGuðmundur Kári Stefánsson, NASA Hubble Fellow, Department of Astrophysical Sciences, Princeton UniversityMegan Delamer, Graduate Student, Department of Astronomy, Penn StateLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2173702023-11-10T00:44:23Z2023-11-10T00:44:23ZWill Saturn’s rings really ‘disappear’ by 2025? An astronomer explains<figure><img src="https://images.theconversation.com/files/558725/original/file-20231109-23-mux310.jpg?ixlib=rb-1.1.0&rect=359%2C215%2C3269%2C1562&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://images.nasa.gov/details/PIA17218">NASA/JPL-Caltech/Space Science Institute</a></span></figcaption></figure><p>If you can get your hands on a telescope, there are few sights more spectacular than the magnificent ringed planet – <a href="https://science.nasa.gov/saturn/">Saturn</a>.</p>
<p>Currently, Saturn is <a href="https://stellarium-web.org/">clearly visible in the evening sky</a>, at its highest just after sunset. It’s the ideal time to use a telescope or binoculars to get a good view of the Solar System’s sixth planet and its famous rings.</p>
<p>But in the past few days, a slew of articles have run like wildfire through social media. Saturn’s rings, those articles claim, <a href="https://www.earth.com/news/saturns-rings-will-vanish-from-sight-in-2025/">are rapidly disappearing</a> – and will be gone by 2025!</p>
<p>So what’s the story? Could the next couple of months, before Saturn drops out of view in the evening sky, really be our last chance to see its mighty rings? </p>
<p>The short answer is <strong>no</strong>. While it’s true the rings will become almost invisible from Earth in 2025, this is neither a surprise nor reason to panic. The rings will “reappear” soon thereafter. Here’s why.</p>
<h2>Tipping and tilting Earth</h2>
<p>To understand why our view of Saturn changes, let’s begin by considering Earth on its constant journey around the Sun. That journey takes us through the seasons – from winter to spring, summer and autumn, then back again. </p>
<p>What causes the seasons? Put simply, Earth is tilted towards one side, as seen from the Sun. Our equator is tilted by about 23.5 degrees from the plane of our orbit. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/558734/original/file-20231109-15-9f73cj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram of Earth showing its position during solstices and equinoxes" src="https://images.theconversation.com/files/558734/original/file-20231109-15-9f73cj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/558734/original/file-20231109-15-9f73cj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=440&fit=crop&dpr=1 600w, https://images.theconversation.com/files/558734/original/file-20231109-15-9f73cj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=440&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/558734/original/file-20231109-15-9f73cj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=440&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/558734/original/file-20231109-15-9f73cj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=553&fit=crop&dpr=1 754w, https://images.theconversation.com/files/558734/original/file-20231109-15-9f73cj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=553&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/558734/original/file-20231109-15-9f73cj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=553&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Earth has seasons because its axis is tilted. The axis always points in the same direction as our planet orbits the Sun.</span>
<span class="attribution"><a class="source" href="https://media.bom.gov.au/social/blog/1762/solstices-and-equinoxes-the-reasons-for-the-seasons/">Bureau of Meteorology</a></span>
</figcaption>
</figure>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/what-is-a-solstice-an-astronomer-explains-the-long-and-short-of-days-years-and-seasons-208178">What is a solstice? An astronomer explains the long and short of days, years and seasons</a>
</strong>
</em>
</p>
<hr>
<p>The result? As we move around the Sun, we alternately tip one hemisphere and then the other towards our star. When your home hemisphere is tilted more towards the Sun, you get longer days than nights and experience spring and summer. When you’re tilted away, you get shorter days and longer nights, and experience autumn and winter. </p>
<p>From the Sun’s viewpoint, Earth appears to “nod” up and down, alternately showing off its hemispheres as it moves around our star. Now, let’s move on to Saturn.</p>
<h2>Saturn, a giant tilted world</h2>
<p>Just like Earth, Saturn experiences seasons, but more than 29 times longer than ours. Where Earth’s equator is tilted by 23.5 degrees, Saturn’s equator has a 26.7 degree tilt. The result? As Saturn moves through its 29.4-year orbit around our star, it also appears to nod up and down as seen from both Earth and the Sun.</p>
<p>What about Saturn’s rings? The planet’s enormous ring system, comprised of bits of ice, dust and rocks, spreads out over a huge distance – <a href="https://science.nasa.gov/saturn/facts/">just over 280,000km from the planet</a>. But it’s very thin – in most places, just tens of metres thick. The rings orbit directly above Saturn’s equator and so they too are tilted to the plane of Saturn’s orbit. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/558739/original/file-20231109-17-qluj40.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Saturn and its rings, tilted at Saturnian midsummer" src="https://images.theconversation.com/files/558739/original/file-20231109-17-qluj40.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/558739/original/file-20231109-17-qluj40.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=469&fit=crop&dpr=1 600w, https://images.theconversation.com/files/558739/original/file-20231109-17-qluj40.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=469&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/558739/original/file-20231109-17-qluj40.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=469&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/558739/original/file-20231109-17-qluj40.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=589&fit=crop&dpr=1 754w, https://images.theconversation.com/files/558739/original/file-20231109-17-qluj40.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=589&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/558739/original/file-20231109-17-qluj40.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=589&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A mosaic of images from NASA’s Cassini mission taken in 2016, highlighting Saturn’s axial tilt during its northern hemisphere summer.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/lightsinthedark/49999550421">NASA/JPL-Caltech/SSI. Composite by Jason Major via Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-sa/4.0/">CC BY-NC-SA</a></span>
</figcaption>
</figure>
<h2>So why do Saturn’s rings ‘disappear’?</h2>
<p>The rings are so thin that, seen from a distance, they appear to vanish when edge on. You can visualise this easily by grabbing a sheet of paper, and rotating it until it is edge on – the paper almost vanishes from view.</p>
<p>As Saturn moves around the Sun, our viewpoint changes. For half of the orbit, its northern hemisphere is tilted towards us and the northern face of the planet’s rings is tipped our way. </p>
<p>When Saturn is on the other side of the Sun, its southern hemisphere is pointed our way. For the same reason, we see the southern face of the planet’s rings tilted our way.</p>
<p>The best way to illustrate this is to get your sheet of paper, and hold it horizontally – parallel to the ground – at eye level. Now, move the paper down towards the ground a few inches. What do you see? The upper side of the paper comes into view. Move the paper back up, through your eye line, to hold it above you and you can see the underside of the paper. But as it passes through eye level, the paper will all but disappear.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/558740/original/file-20231109-26-lli6wh.gif?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/558740/original/file-20231109-26-lli6wh.gif?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/558740/original/file-20231109-26-lli6wh.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=384&fit=crop&dpr=1 600w, https://images.theconversation.com/files/558740/original/file-20231109-26-lli6wh.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=384&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/558740/original/file-20231109-26-lli6wh.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=384&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/558740/original/file-20231109-26-lli6wh.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=483&fit=crop&dpr=1 754w, https://images.theconversation.com/files/558740/original/file-20231109-26-lli6wh.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=483&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/558740/original/file-20231109-26-lli6wh.gif?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=483&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">This simulation demonstrates the 29.5-year orbital period of Saturn, as viewed from Earth. The ring system lies directly above Saturn’s equator, so both sides of its disk are visible from Earth during the course of one Saturnian year.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Saturnoppositions-animated.gif">Tdadamemd/Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>That’s what we see with Saturn’s rings. As the seasons on Saturn progress, we go from having the southern side of the rings tilted our way to seeing the northern side. Then, the planet tips back, revealing the southern side once more.</p>
<p>Twice per Saturnian year, we see the rings edge on and they all but vanish from view.</p>
<p>That’s what’s happening in 2025 – the reason Saturn’s rings will seemingly “disappear” is because we will be looking at them edge on.</p>
<p>This happens regularly. The last time was in 2009 and the rings gradually became visible again, over the course of a few months. The rings will be edge on once again in March 2025. Then they’ll gradually come back into view as seen through large telescopes, before sliding out of view again in November 2025. </p>
<p>Thereafter, the rings will gradually get more and more obvious, reappearing first to the largest telescopes over the months that follow. Nothing to worry about.</p>
<p>If you want to clearly see Saturn’s rings, now is your best chance, at least until 2027 or 2028!</p><img src="https://counter.theconversation.com/content/217370/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jonti Horner does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Viral headlines would have you think Saturn’s rings will vanish in just 18 months. Here’s what that really means and why you don’t need to worry.Jonti Horner, Professor (Astrophysics), University of Southern QueenslandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2144442023-10-26T10:30:15Z2023-10-26T10:30:15ZThe Sun’s activity cycle is reaching its peak early: knowing why could help us unlock the secrets of our star<figure><img src="https://images.theconversation.com/files/554595/original/file-20231018-21-ojnm6l.jpg?ixlib=rb-1.1.0&rect=12%2C0%2C4065%2C2152&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">An image from January 2023 showing an X1.2 class flare erupting on the Sun (far left hand side).</span> <span class="attribution"><a class="source" href="https://svs.gsfc.nasa.gov/14270/">NASA/GSFC/SDO</a></span></figcaption></figure><p>Our Sun is a steady and everlasting companion. Reliable like a clock, its apparent passage across the sky allows us to measure time. The Sun and its path is also the source of Earth’s seasons. But in many respects, our Sun is far from calm and unchanging.</p>
<p>Close up, the Sun shows extensive <a href="https://spaceplace.nasa.gov/solar-activity/en/">variation and activity</a>. Bright explosions called <a href="https://hesperia.gsfc.nasa.gov/sftheory/flare.htm">flares</a> regularly cause huge outbreaks of radiation. Darker, cooler areas <a href="https://www.space.com/sunspots-formation-discovery-observations">called sunspots</a> emerge, move, change shape and vanish. The Sun also releases material into space in powerful eruptions, called <a href="https://en.wikipedia.org/wiki/Solar_particle_event">solar particle events</a>.</p>
<p>This solar activity varies with time. It peaks every 11 years – and the next high point had been <a href="https://www.weather.gov/news/201509-solar-cycle">forecast for July 2025</a>. But it now looks as if this “solar maximum” will arrive earlier than expected. This finding could lead to a better understanding of our host star.</p>
<p>Solar activity also affects Earth and the technology we rely on. Solar particle events can disable satellites and disrupt electrical grids. Activity from the Sun that affects our planet is often referred to as “space weather”.</p>
<h2>Timing matters</h2>
<p>To ensure we can make forecasts and prepare, we need a good set of rules – a scientific model. Nasa and the US National Oceanic and Atmospheric Administration have been creating these for many years.</p>
<p>They merge a variety of methods to <a href="https://www.swpc.noaa.gov/products/solar-cycle-progression#:%7E:text=The%20Prediction%20Panel%20predicted%20Cycle,November%202024%20and%20March%202026.&text=SWPC%20Space%20Weather%20Operations%20(SWO)%2C%20Daily%20Observations.">predict solar activity</a>. This approach has yielded a date for the next solar maximum (the peak) of around July 2025. This peak was also forecast to be relatively weak, like the maximum during the previous solar cycle. This lasted from about December 2008 to December 2019, with a peak in April 2014.</p>
<p>However, an <a href="https://link.springer.com/article/10.1007/s11207-020-1595-3">alternative forecast</a> has been published by a team led by Nasa scientist Robert Leamon and Scott McIntosh, deputy director at the US National Centre for Atmospheric Research (NCAR). They say the cycle’s peak will occur a year earlier in mid-late 2024 and sunspot numbers will be twice the official prediction – an indication of activity. Observations of the Sun currently support this alternative forecast. </p>
<p>What’s interesting is that many prediction methods rely on timing the length of a cycle measured by the minimum (lowest point) of solar activity. But Leamon and McIntosh looked in more depth at the actual sunspots and their magnetic properties. When a solar cycle ends, it is not instantaneous. It is a gentle transition where fewer sunspots appear with magnetic properties linked to the old cycle and more appear with properties linked to the new cycle. </p>
<p>This current prediction uses the terminator – the time when the very last sunspot of the old cycle has faded – to indicate the end of that solar cycle. This can result in different timings for the length of a cycle. For example, the <a href="https://www.weather.gov/news/201509-solar-cycle">last minimum was December 2019</a> but the terminator actually happened in December 2021. The research group was then able to develop predictions for how strong the upcoming cycle would be by looking at how long the previous one was.</p>
<h2>In the line of fire</h2>
<p>But what would higher solar activity mean for us, as the cycle shortly reaches its peak? As the Sun releases vast amounts of energy as flares and other events that eject material into space, <a href="https://www.swpc.noaa.gov/phenomena/coronal-mass-ejections">there is a chance that some will hit Earth</a> if we are in the line of fire. Luckily, Earth has its own magnetic shield that can protect us.</p>
<p>As particles and magnetic fields from the Sun reach us, they first interact with Earth’s own magnetic field, causing it to be buffeted and squashed. It also forces solar particles to move in a way dictated by Earth’s magnetic fields. This traps them to some extent, preventing them from hitting the Earth’s surface.</p>
<figure class="align-center ">
<img alt="Aurora" src="https://images.theconversation.com/files/554822/original/file-20231019-19-oa6m6f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/554822/original/file-20231019-19-oa6m6f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=353&fit=crop&dpr=1 600w, https://images.theconversation.com/files/554822/original/file-20231019-19-oa6m6f.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=353&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/554822/original/file-20231019-19-oa6m6f.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=353&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/554822/original/file-20231019-19-oa6m6f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=444&fit=crop&dpr=1 754w, https://images.theconversation.com/files/554822/original/file-20231019-19-oa6m6f.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=444&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/554822/original/file-20231019-19-oa6m6f.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=444&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Auroras are caused by interactions between solar particles and the Earth’s magnetic field.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/northern-lights-over-snowy-mountains-aurora-2222259423">Abstract51 / Shutterstock</a></span>
</figcaption>
</figure>
<p>Although Earth’s magnetic “shield” gives us a degree of protection, solar activity still affects us. Examples of this are the <a href="https://www.jpl.nasa.gov/nmp/st5/SCIENCE/aurora.html">northern (or southern) lights</a>. These occur when solar particles reach the high atmosphere and “excite” atoms there, causing them to move to a high energy state. As the atoms relax, they emit light in different colours – for example as reds, greens and blues. This stunning display is ideally viewed closer to our planet’s magnetic poles. </p>
<p>Solar activity can cause power surges in the long transmission lines used in electrical grids. One example was the <a href="https://spaceweatherarchive.com/2021/03/12/the-great-quebec-blackout/">1989 power blackout in Quebec, Canada</a>.</p>
<p>Other effects include a change of particle density in the high atmosphere. This can result in minor errors on devices using GPS. It can also lead to slight heating of our outer atmosphere, making it extend further into space. This increases the thickness of the atmosphere for satellites in low Earth orbit. </p>
<p>This can cause them to lose altitude and, sometimes, burn up. One such event <a href="https://www.space.com/spacex-starlink-satellites-lost-geomagnetic-storm">affected a batch of new StarLink satellites</a> launched by SpaceX in February 2022. This event occurred when the Sun was showing roughly half the activity we’re currently experiencing. </p>
<p>When solar activity grows stronger, it’s more likely that a solar storm could strike us, causing electrical problems on satellites. Those spacecraft may need to be put into what’s called “safe mode” where many systems are switched off. This allows them to sit out the storm.</p>
<figure class="align-center ">
<img alt="GPS III satellite." src="https://images.theconversation.com/files/554824/original/file-20231019-19-el47p9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/554824/original/file-20231019-19-el47p9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=422&fit=crop&dpr=1 600w, https://images.theconversation.com/files/554824/original/file-20231019-19-el47p9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=422&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/554824/original/file-20231019-19-el47p9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=422&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/554824/original/file-20231019-19-el47p9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=531&fit=crop&dpr=1 754w, https://images.theconversation.com/files/554824/original/file-20231019-19-el47p9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=531&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/554824/original/file-20231019-19-el47p9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=531&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Solar activity can cause location errors when using GPS devices.</span>
<span class="attribution"><a class="source" href="https://www.spaceforce.mil/Multimedia/Photos/igphoto/2002516820/">Lockheed Martin and U.S. Space Force</a></span>
</figcaption>
</figure>
<p>Our society is constantly developing in ways that make us more reliant on electrical infrastructure. We are also expanding our technology into space – technology which is vulnerable if we don’t monitor space weather and its source, the Sun. If we know what’s coming, we can prepare. Electrical grids are being designed to be less prone to power surges and satellites are being designed to better ride out space weather. </p>
<p>But we need a deeper understanding of our star. Experts already keep a <a href="https://www.sidc.be/SILSO/home">detailed log of past observations</a> and are constantly extending their ways of <a href="https://science.nasa.gov/mission/parker-solar-probe/">observing the Sun and space weather using satellites</a>. We are also improving scientific models that let us predict solar activity. This current, surprising solar cycle will enhance our ability to do that.</p><img src="https://counter.theconversation.com/content/214444/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Daniel Brown does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>A more active Sun could disable satellites and affect electrical grids on Earth.Daniel Brown, Lecturer in Astronomy, Nottingham Trent UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2133422023-10-11T12:30:02Z2023-10-11T12:30:02ZComets 101 − everything you need to know about the snow cones of space<figure><img src="https://images.theconversation.com/files/551230/original/file-20230929-15-mbvm9p.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C1200%2C1200&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Comet Hale-Bopp was visible from Earth in 1997.</span> <span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Comet_Hale-Bopp_1995O1.jpg">E. Kolmhofer, H. Raab; Johannes-Kepler-Observatory, Linz, Austria</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span></figcaption></figure><p>When you hear the word comet, you might imagine a bright streak moving across the sky. You may have a family member who saw a comet before you were born, or you may have seen one yourself when <a href="https://www.livescience.com/space/comets/green-comet-nishimura-survives-its-superheated-slingshot-around-the-sun-will-we-get-another-chance-to-see-it">comet Nishimura passed by Earth</a> in September 2023. But what are these special celestial objects made of? Where do they come from, and why do they have such long tails?</p>
<p>As a <a href="https://msutoday.msu.edu/for-media/experts/details?u=shannon.schmoll">planetarium director</a>, I spend most of my time getting people excited about and interested in space. Nothing piques people’s interest in Earth’s place in the universe quite like comets. They’re unpredictable, and they often go undetected until they get close to the Sun. I still get excited when one comes into view.</p>
<h2>What exactly is a comet?</h2>
<p>Comets are leftover material from the formation of the solar system. As the solar system formed about <a href="https://science.nasa.gov/solar-system/facts/">4.5 billion years ago</a>, most gas, dust, rock and metal ended up in the Sun or the planets. What did not get captured was <a href="https://solarsystem.nasa.gov/solar-system/our-solar-system/in-depth/">left over as comets and asteroids</a>. </p>
<p>Because <a href="https://www.universetoday.com/40692/what-are-comets-made-of/">comets are</a> clumps of rock, dust, ice and the frozen forms of various gases and molecules, <a href="https://adsabs.harvard.edu/full/1989ESASP.302...39K">they’re often called</a> “dirty snowballs” or “icy dirtballs” by astronomers. Theses clumps of ice and dirt make up what’s called the comet nucleus.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/549442/original/file-20230920-29-htg22i.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram showing comet nuclei, which look like gray rocks, of progressively larger sizes." src="https://images.theconversation.com/files/549442/original/file-20230920-29-htg22i.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/549442/original/file-20230920-29-htg22i.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=296&fit=crop&dpr=1 600w, https://images.theconversation.com/files/549442/original/file-20230920-29-htg22i.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=296&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/549442/original/file-20230920-29-htg22i.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=296&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/549442/original/file-20230920-29-htg22i.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=373&fit=crop&dpr=1 754w, https://images.theconversation.com/files/549442/original/file-20230920-29-htg22i.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=373&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/549442/original/file-20230920-29-htg22i.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=373&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Size comparison of various comet nuclei.</span>
<span class="attribution"><a class="source" href="https://hubblesite.org/contents/media/images/2022/020/01FZGSSNBGK1ZSFW2DCS2GYFZC?news=true">NASA, ESA, Zena Levy (STScI)</a></span>
</figcaption>
</figure>
<p>Outside the nucleus is a porous, almost fluffy layer of ice, kind of like a snow cone. This layer is surrounded by a <a href="https://www.jpl.nasa.gov/news/why-comets-are-like-deep-fried-ice-cream">dense crystalline crust</a>, which forms when the comet passes near the Sun and its outer layers heat up. With a crispy outside and a fluffy inside, astronomers have compared comets to <a href="https://www.nasa.gov/jpl/rosetta/why-comets-are-like-deep-fried-ice-cream">deep-fried ice cream</a>.</p>
<p>Most comets are <a href="https://www.vanderbilt.edu/AnS/physics/astrocourses/AST101/readings/comets.html">a few miles wide</a>, and the largest known is <a href="https://www.nasa.gov/feature/goddard/2022/hubble-confirms-largest-comet-nucleus-ever-seen">about 85 miles</a> wide. Because they are relatively small and dark compared with other objects in the solar system, people can’t see them unless the comet gets close to the Sun.</p>
<h2>Pin the tail on the comet</h2>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/551217/original/file-20230929-25-us7tnz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Starry sky with a comet in the mid left portion of the image and a tree in the foreground" src="https://images.theconversation.com/files/551217/original/file-20230929-25-us7tnz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/551217/original/file-20230929-25-us7tnz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=783&fit=crop&dpr=1 600w, https://images.theconversation.com/files/551217/original/file-20230929-25-us7tnz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=783&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/551217/original/file-20230929-25-us7tnz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=783&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/551217/original/file-20230929-25-us7tnz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=983&fit=crop&dpr=1 754w, https://images.theconversation.com/files/551217/original/file-20230929-25-us7tnz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=983&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/551217/original/file-20230929-25-us7tnz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=983&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Comet Hale-Bopp as seen from Earth in 1997. The blue ion tail is visible to the top left of the comet.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Comet-Hale-Bopp-29-03-1997_hires.jpg">Philipp Salzgeber</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>As a comet moves close to the Sun, it heats up. The various frozen gases and molecules making up the comet change directly from solid ice to gas in a <a href="https://www.britannica.com/science/sublimation-phase-change">process called sublimation</a>. This sublimation process releases dust particles trapped under the comet’s surface. </p>
<p>The dust and released gas form a cloud around the comet called a coma. This gas and dust interact with the Sun to form <a href="https://skyandtelescope.org/astronomy-resources/why-do-comets-have-tails/">two different tails</a>. </p>
<p>The first tail, made up of gas, is called <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/comet-tails">the ion tail</a>. The Sun’s radiation strips electrons from the gases in the coma, leaving them with a positive charge. These charged gases are called ions. Wind from the Sun then pushes these charged gas particles directly away from the Sun, forming a tail that appears blue in color. The blue color comes from large numbers of <a href="https://astronomy.swin.edu.au/cosmos/c/Cometary+Gas+Tail">carbon monoxide</a> ions in the tail.</p>
<p>The dust tail forms from the dust particles released during sublimation. These are pushed away from the Sun by <a href="https://science.nasa.gov/structured-tails-comet-neowise">pressure caused by the Sun’s light</a>. The tail reflects the sunlight and swoops behind the comet as it moves, giving <a href="https://spaceplace.nasa.gov/comets/en/">the comet’s tail a curve</a>. </p>
<p>The closer a comet gets to the Sun, the longer and brighter its tail will grow. The tail can grow significantly longer than the nucleus and clock in around <a href="https://coolcosmos.ipac.caltech.edu/ask/182-What-is-the-size-of-a-comet-">half a million miles long</a>. </p>
<h2>Where do comets come from?</h2>
<p>All comets have <a href="https://www.st-andrews.ac.uk/%7Ebds2/ltsn/ljm/JAVA/COMETORB/COMET.HTM">highly eccentric orbits</a>. Their paths are elongated ovals with extreme trajectories that take them both very close to and very far from the Sun. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/Ia1k4Jec1Dc?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Comets’ orbits can be very long, meaning they may spend most of their time in far-off reaches of the solar system.</span></figcaption>
</figure>
<p>An object will <a href="https://solarsystem.nasa.gov/resources/310/orbits-and-keplers-laws/">orbit faster the closer it is</a> to the Sun, as <a href="https://www.britannica.com/science/Keplers-second-law-of-planetary-motion">angular momentum is conserved</a>. Think about how an <a href="https://news.unl.edu/newsrooms/today/article/physics-of-olympian-feats-spinning-figure-skater/">ice skater spins faster</a> when they bring their arms in closer to their body – similarly, comets speed up when they get close to the Sun. Otherwise, comets spend most of their time moving relatively slowly through the outer reaches of the solar system.</p>
<p>A lot of comets likely originate in a far-out region of our solar system called <a href="https://solarsystem.nasa.gov/solar-system/oort-cloud/overview/">the Oort cloud</a>. </p>
<p>The Oort cloud is predicted to be a round shell of <a href="https://science.nasa.gov/planetary-science/focus-areas/small-bodies-solar-system/">small solar system bodies</a> that surround the Earth’s solar system with an innermost boundary about 2,000 times farther from the Sun than Earth. For reference, Pluto is only about <a href="https://solarsystem.nasa.gov/planets/dwarf-planets/pluto/in-depth/">40 times farther</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/551201/original/file-20230929-27-56dxz8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Sphere of small particles with a disk like structure in the middle. A tiny rectangle in the center points to a zoomed in image of the Sun and planet orbits" src="https://images.theconversation.com/files/551201/original/file-20230929-27-56dxz8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/551201/original/file-20230929-27-56dxz8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=515&fit=crop&dpr=1 600w, https://images.theconversation.com/files/551201/original/file-20230929-27-56dxz8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=515&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/551201/original/file-20230929-27-56dxz8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=515&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/551201/original/file-20230929-27-56dxz8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=647&fit=crop&dpr=1 754w, https://images.theconversation.com/files/551201/original/file-20230929-27-56dxz8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=647&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/551201/original/file-20230929-27-56dxz8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=647&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A NASA diagram of the Oort cloud’s structure. The term KBO refers to Kuiper Belt objects near where Pluto lies.</span>
<span class="attribution"><a class="source" href="https://solarsystem.nasa.gov/resources/491/oort-cloud/">NASA</a></span>
</figcaption>
</figure>
<p>Comets from the Oort cloud take over 200 years to complete their orbits, a metric called the orbital period. Because of their long periods, they’re called <a href="https://astronomy.swin.edu.au/cosmos/l/Long-period+Comets">long-period comets</a>. Astronomers often don’t know much about these comets until they get close to the inner solar system. </p>
<p><a href="https://starchild.gsfc.nasa.gov/docs/StarChild/questions/question40.html">Short-period comets</a>, on the other hand, have orbital periods of less than 200 years. Halley’s comet is a famous comet that comes close to the Sun every 75 years. </p>
<p>While that’s a long time for a human, that’s a short period for a comet. Short-period comets generally come from the <a href="https://solarsystem.nasa.gov/solar-system/kuiper-belt/overview/">Kuiper Belt</a>, an asteroid belt out beyond Neptune and, most famously, the home of Pluto. </p>
<p>There’s a subset of short-period comets that get only to about Jupiter’s orbit at their farthest point from the Sun. These have orbital periods of less than 20 years and are called <a href="https://astronomy.swin.edu.au/cosmos/J/Jupiter-family+comets">Jupiter-family comets</a>.</p>
<p>Comets’ time in the inner solar system is relatively short, generally on the order of <a href="https://eyes.nasa.gov/apps/asteroids/#/home">weeks to months</a>. As they approach the Sun, their tails grow and they brighten before fading on their way back to the outer solar system. </p>
<p>But even the short-period comets don’t come around often, and their porous interior means they can sometimes fall apart. All of this makes their behavior <a href="https://www.space.com/20347-comet-brightness-predictions-difficult.html">difficult to predict</a>. Astronomers can track comets when they are coming toward the inner solar system and make predictions based on observations. But they never quite know if a comet will get bright enough to be seen with the naked eye as it passes Earth, or if it will fall apart and fizzle out as it enters the inner solar system. </p>
<p>Either way, comets will keep people looking up at the skies for years to come.</p><img src="https://counter.theconversation.com/content/213342/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Shannon Schmoll receives funding from National Science Foundation, president-elect of the International Planetarium Society, and treasurer of the Great Lakes Planetarium Association.</span></em></p>There’s a flurry of excitement every time a comet comes into view from Earth. But what are these celestial objects, and where do they come from?Shannon Schmoll, Director of the Abrams Planetarium, Michigan State UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2134532023-10-11T03:12:00Z2023-10-11T03:12:00ZHow should I add sunscreen to my skincare routine now it’s getting hotter?<figure><img src="https://images.theconversation.com/files/551609/original/file-20231003-17-n2lo07.jpg?ixlib=rb-1.1.0&rect=14%2C110%2C4905%2C3164&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://unsplash.com/photos/xOEmZX6YSu8">Annie Spratt/Unsplash</a></span></figcaption></figure><p>Sun exposure is the number one cause of skin cancer – including the most deadly form, melanoma. High levels of sun exposure cause <a href="https://europepmc.org/article/MED/26437734#id580549">an estimated 7,200 melanomas in Australia each year</a>. </p>
<p>Too much sun exposure can also lead to premature ageing, resulting in wrinkles, fine lines and age spots. </p>
<p>Can a tweak to your skincare routine help prevent this?</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/sunscreen-heres-why-its-an-anti-ageing-skincare-essential-187322">Sunscreen: here’s why it’s an anti-ageing skincare essential</a>
</strong>
</em>
</p>
<hr>
<h2>When should I start wearing sunscreen?</h2>
<p>In Australia, we are advised to <a href="https://pubmed.ncbi.nlm.nih.gov/30681231/">wear sunscreen</a> on days when the ultraviolet (UV) index reaches three or higher. That’s year-round for much of Australia. The weather forecast or the Cancer Council’s free <a href="https://www.sunsmart.com.au/resources/sunsmart-app">SunSmart app</a> are easy ways to check the UV Index.</p>
<p>Besides “primary sunscreens”, which are dedicated sun-protection products, a sun protection factor (SPF) is also found in many beauty products, such as foundations, powders and moisturisers. These are called “secondary sunscreens” because they have a primary purpose other than sun protection. </p>
<p>Primary sunscreens are regulated by the <a href="https://www.tga.gov.au/news/news/about-sunscreens#_Sun_protection_factor">Therapeutic Goods Administration</a> and the SPF must be determined by testing on human skin. SPF measures how quickly skin burns with and without the sunscreen under intense UV light. If the skin takes ten seconds to burn with no sunscreen, and 300 seconds to burn with the sunscreen, the SPF is 30 (300 divided by 10).</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1617699959146688514"}"></div></p>
<h2>Is the SPF in makeup or moisturisers enough to protect me the whole day?</h2>
<p>Simple answer? No. SPF 30 mixed into foundation is not going to be as effective as a primary SPF 30 sunscreen. </p>
<p>Also, when people use a moisturiser or makeup that includes SPF, they generally don’t do the three key steps that make sunscreens effective: </p>
<ol>
<li>putting a thick enough amount on</li>
<li>covering all sun exposed areas</li>
<li>reapplying regularly when outdoors for a sustained amount of time.</li>
</ol>
<p>One <a href="https://pubmed.ncbi.nlm.nih.gov/37632801/">study</a> had 39 participants apply their usual SPF makeup/moisturisers and photographed them with UV photography in the morning, then again in the afternoon, without reapplying during the day. The UV photography allowed the researchers to visualise how much protection these products were still providing. </p>
<p>They found participants missed some facial areas with the initial application and the SPF products provided less coverage by the afternoon.</p>
<figure class="align-right ">
<img alt="Woman applies makeup" src="https://images.theconversation.com/files/551610/original/file-20231003-27-zqq5eo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/551610/original/file-20231003-27-zqq5eo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=900&fit=crop&dpr=1 600w, https://images.theconversation.com/files/551610/original/file-20231003-27-zqq5eo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=900&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/551610/original/file-20231003-27-zqq5eo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=900&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/551610/original/file-20231003-27-zqq5eo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1131&fit=crop&dpr=1 754w, https://images.theconversation.com/files/551610/original/file-20231003-27-zqq5eo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1131&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/551610/original/file-20231003-27-zqq5eo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1131&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Consider how much you’re using.</span>
<span class="attribution"><a class="source" href="https://www.pexels.com/photo/woman-in-black-blazer-and-white-shirt-4612152/">Pexels/Cottonbro Studio</a></span>
</figcaption>
</figure>
<p>Another consideration is the product type. Liquid foundation may be applied more thickly than powder makeup, which is generally lightly applied. </p>
<p>The <a href="https://www.tga.gov.au/products/medicines/sunscreens">Therapeutic Goods Administration</a> tests primary sunscreens so they’re effective when applied at 2mg per 2 square centimetres of skin.</p>
<p>For the face, ears and neck, this is about one teaspoon (5mL) – are you applying that much powder?</p>
<p>It’s unlikely people will cake on their moisturiser thickly and reapply during the day, so these products aren’t effective sun protection if outdoors for a sustained amount of time when used alone.</p>
<h2>If skin products with SPF aren’t giving me better protection, should I stop using them?</h2>
<p>These products can still serve a protective purpose, as <a href="https://onlinelibrary.wiley.com/doi/10.1111/srt.13010">some research</a> suggests layering sunscreen and makeup products may help to cover areas that were missed during a single application. </p>
<p>When layering, SPF factors are not additive. If wearing an SPF 30 sunscreen and makeup with SPF 15, that doesn’t equal SPF 45. You will be getting the protection from the highest product (in this scenario, it’s the SPF 30). </p>
<p>A good metaphor is SPF in makeup is like “icing on the cake”. Use it as an add-on and if areas were missed with the initial sunscreen application, then there is another chance to cover all areas with the SPF makeup.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/explainer-how-does-sunscreen-work-what-is-spf-and-can-i-still-tan-with-it-on-88869">Explainer: how does sunscreen work, what is SPF and can I still tan with it on?</a>
</strong>
</em>
</p>
<hr>
<h2>Should I apply sunscreen before or after makeup?</h2>
<p>It depends on whether you’re using a chemical or physical sunscreen. Chemical sunscreens need to absorb into the skin to block and absorb the sun’s rays, whereas physical sunscreens sit on the surface of the skin and act as a shield. </p>
<p>When the main ingredient is zinc oxide or titanium dioxide, it’s a physical sunscreen – think the classic zinc sticks you used to apply to your nose and lips at the beach. Physical sunscreens are recommended for people with sensitive skin and although they used to be pretty thick and sticky, newer versions feel more like chemical sunscreens. </p>
<p>For maximum sun protection when using chemical sunscreens, apply sunscreen first, followed by moisturiser, then makeup. Give the sunscreen a few minutes to dry and sink into the skin before starting to put on other products. Chemical sunscreen should be applied 20 minutes before going outdoors.</p>
<figure class="align-center ">
<img alt="Man puts sunscreen on his face" src="https://images.theconversation.com/files/551611/original/file-20231003-25-4yrdir.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/551611/original/file-20231003-25-4yrdir.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/551611/original/file-20231003-25-4yrdir.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/551611/original/file-20231003-25-4yrdir.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/551611/original/file-20231003-25-4yrdir.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/551611/original/file-20231003-25-4yrdir.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/551611/original/file-20231003-25-4yrdir.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=502&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Give chemical sunscreen a few minutes to dry before applying moisturiser.</span>
<span class="attribution"><a class="source" href="https://www.pexels.com/photo/man-putting-on-cream-on-his-face-7433339/">Pexels/August de Richelieu</a></span>
</figcaption>
</figure>
<p>When using a physical sunscreen, first apply moisturisers, followed by sunscreen, and then makeup.</p>
<p>When reapplying sunscreen, it’s recommended to wash off makeup and start fresh, but this isn’t going to be practical for many people, so gently patting sunscreen over makeup is another option. Physical sunscreens will be most effective for reapplication over makeup.</p>
<h2>What type of sunscreen should I use?</h2>
<p>The best sunscreen is the one you actually like to apply. Protecting your skin on a daily basis (and not just for trips to the beach!) is a must in Australia’s high UV climate, and should be done with a primary sunscreen.</p>
<p>Look for sunscreens that have the label “broad spectrum”, which means it covers for UVA and UVB, and has at least SPF30. </p>
<p>Then experiment with features like matte finish, milk texture or fragrance-free to find a sunscreen you like.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/how-to-pick-the-right-sunscreen-when-youre-blinded-by-choice-125881">How to pick the right sunscreen when you're blinded by choice</a>
</strong>
</em>
</p>
<hr>
<p>No sunscreen provides 100% protection so you should also use other sun protection such as protective clothing, hats, sunglasses, using shade and avoiding the sun during peak UV hours.</p>
<p>Skin care and makeup products with SPF is better than nothing, but don’t rely solely on your morning makeup for sun protection the entire day.</p><img src="https://counter.theconversation.com/content/213453/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Monika Janda receives funding from National Health and Medical Research Council, Medical Research Future Fund and Australian Cancer Research Foundation. </span></em></p><p class="fine-print"><em><span>Katie Lee receives funding from the National Health and Medical Research Council. </span></em></p><p class="fine-print"><em><span>Caitlin Horsham does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Does SPF in makeup and moisturisers provide effective sun protection?Monika Janda, Professor in Behavioural Science, The University of QueenslandCaitlin Horsham, Research Manager, The University of QueenslandKatie Lee, PhD Candidate, The University of QueenslandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2099552023-08-14T18:42:58Z2023-08-14T18:42:58ZThis solar cycle, the sun’s activity is more powerful and surprising than predicted<figure><img src="https://images.theconversation.com/files/541795/original/file-20230808-15-85ytq4.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C1920%2C1080&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A coronal mass ejection on the solar surface.</span> <span class="attribution"><span class="source">(NASA/GSFC/SDO)</span></span></figcaption></figure><iframe style="width: 100%; height: 100px; border: none; position: relative; z-index: 1;" allowtransparency="" allow="clipboard-read; clipboard-write" src="https://narrations.ad-auris.com/widget/the-conversation-canada/this-solar-cycle-the-suns-activity-is-more-powerful-and-surprising-than-predicted" width="100%" height="400"></iframe>
<p>What do you feel when you see the aurora? </p>
<p>Otherwise known as the northern or southern lights, an aurora is light emitted by upper atmospheric particles as they interact with energized ones <a href="https://superdarn.ca/tutorials-11">from the magnetosphere</a>.</p>
<p>It’s an awe-inspiring and otherworldly event that those living at high latitudes can experience often. In <a href="https://creeliteracy.org/2018/05/01/northern-lights-creesimonsays/">Cree and Ojibwe teachings</a>, the northern lights are ancestral spirits who remain and communicate from the sky. </p>
<p>To scientists, the aurora is an infinitely complex amalgamation of <a href="https://www.nasa.gov/ionosphere">ionospheric</a> dynamics, a manifestation of Earth’s intrinsic connection to the sun. To industry, it’s a risk factor.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/540229/original/file-20230731-17-9pbazi.jpg?ixlib=rb-1.1.0&rect=0%2C2%2C936%2C524&q=45&auto=format&w=1000&fit=clip"><img alt="green lights ribbon in the sky above powerlines" src="https://images.theconversation.com/files/540229/original/file-20230731-17-9pbazi.jpg?ixlib=rb-1.1.0&rect=0%2C2%2C936%2C524&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/540229/original/file-20230731-17-9pbazi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/540229/original/file-20230731-17-9pbazi.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/540229/original/file-20230731-17-9pbazi.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/540229/original/file-20230731-17-9pbazi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=425&fit=crop&dpr=1 754w, https://images.theconversation.com/files/540229/original/file-20230731-17-9pbazi.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=425&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/540229/original/file-20230731-17-9pbazi.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=425&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The aurora borealis seen above the Saskatoon SuperDARN space weather radar.</span>
<span class="attribution"><span class="source">(A. Reimer)</span></span>
</figcaption>
</figure>
<h2>The Starlink destruction event</h2>
<p>In February 2022, <a href="https://www.bbc.com/news/world-60317806">SpaceX launched 49 Starlink internet satellites into a low-Earth orbit (LEO)</a>. This was the 36th Starlink launch that SpaceX had carried out, and one that they anticipated to go off without a hitch, just like the 35 before. </p>
<p>On launch day, a <a href="https://www.swpc.noaa.gov/phenomena/coronal-mass-ejections">coronal mass ejection</a> — a large burst of plasma expelled from the sun — struck Earth. It caused a geomagnetic storm in the atmosphere between around 100 and 500 kilometres in altitude, the target range for Starlink. </p>
<p>This event injected an immense amount of electromagnetic energy straight into Earth’s upper atmosphere. It produced <a href="https://www.youtube.com/watch?v=q_GYySXTtio">beautiful auroral displays</a>, but the energy also increased the density of the air. A higher air density typically isn’t a big deal for LEO satellites, because it’s already extremely low at usual operational altitudes (upwards of 400 kilometres). </p>
<p>Starlink, however, was initially <a href="https://doi.org/10.1029/2022SW003074">launched into an altitude of 210 kilometres</a>. That’s much closer to Earth, with an exponentially higher air density. Thirty-eight out of those 49 initial launch satellites were subsequently lost due to atmospheric drag from the dense atmosphere, <a href="https://doi.org/10.1051/swsc/2022034">pulling them back to Earth</a>.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/mUlAz_Oxv4Q?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Starlink satellites burning up in the atmosphere over Puerto Rico, Feb. 7, 2022.</span></figcaption>
</figure>
<h2>Surprising solar cycle</h2>
<p>The sun undergoes a cycle — an 11-year one, to be exact — from which its activity increases and decreases periodically. At the peak of a cycle, we see more sunspots on the solar surface, more radiation emitted, and more solar flares. Geomagnetic storms like the one that caused the Starlink destruction event are a relatively common occurrence, especially when the sun reaches the peak of its 11-year cycle of strengthening and weakening activity. </p>
<p>In the previous cycle, which ended in 2019 (the 24th tracked cycle since 1755), <a href="https://doi.org/10.1016/j.asr.2022.10.033">there were 927 storms classed as moderate or weak alone</a> — an average of one every five or so days. </p>
<p>We’re currently four years into solar cycle 25, but this one has already proven surprising. The maximum activity of the 25th cycle was predicted to occur in 2025, but solar activity has already exceeded that. This means we’ve been seeing more geomagnetic storms, more auroral displays (and at lower latitudes than usual) and, potentially, more hazardous conditions for LEO satellites.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/540308/original/file-20230731-23-cwg668.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A plotted graph showing solar cycle sunspots" src="https://images.theconversation.com/files/540308/original/file-20230731-23-cwg668.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/540308/original/file-20230731-23-cwg668.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=221&fit=crop&dpr=1 600w, https://images.theconversation.com/files/540308/original/file-20230731-23-cwg668.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=221&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/540308/original/file-20230731-23-cwg668.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=221&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/540308/original/file-20230731-23-cwg668.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=278&fit=crop&dpr=1 754w, https://images.theconversation.com/files/540308/original/file-20230731-23-cwg668.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=278&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/540308/original/file-20230731-23-cwg668.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=278&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Solar activity as the number of sunspots visible on the solar surface. The number of sunspots seen is already considerably higher than what is expected from the solar maximum, two years ahead of schedule.</span>
<span class="attribution"><a class="source" href="https://www.swpc.noaa.gov/products/solar-cycle-progression">(National Oceanic and Atmospheric Administration)</a></span>
</figcaption>
</figure>
<h2>Space weather — the unseen force of nature</h2>
<p>If geomagnetic storms are so common, why don’t they cause more issues? <a href="https://www.maine.gov/mema/maine-prepares/preparedness-library/geomagnetic-storms">The reality is that they do</a>, but the consequences are much less obvious than satellites burning up in the atmosphere.</p>
<p>When space weather energy enters Earth’s upper atmosphere, for example, the ionospheric composition changes in addition to the air getting denser. High-frequency, or “shortwave,” radio communication depends on a predictable ionosphere to broadcast long distances. </p>
<p>Geomagnetic storms that affect ionospheric composition can cause <a href="https://doi.org/10.1029/2018SW002008">radio blackouts</a>, such as a <a href="https://www.space.com/x-class-solar-flare-radio-blackout-august-2023">disruption in North America on Aug. 7</a>. Even minor storms can cause the degradation of radio signals used in military and maritime systems, aviation communication or ham radio. </p>
<p>Extreme storms can cause radio blackouts lasting hours, and for an entire side of the globe. Storms that big can also cause more discernible problems, such as the nine-hour <a href="http://www.hydroquebec.com/learning/notions-de-base/tempete-mars-1989.html">electricity outage experienced by Hydro-Québec in 1989</a>.</p>
<h2>Space weather warning systems</h2>
<p>It’s not all doom and disintegrating rockets, however. We can detect when a solar flare leaves the surface of the sun and predict roughly when it will affect the Earth, giving forewarning to certain types of storms and <a href="https://www.aurorawatch.ca/">chances to see the aurora</a>.</p>
<p>For many storms however, there is very little or no predictive capability because it depends on how the Earth’s magnetic field interacts with the solar wind, which is harder to see. </p>
<p>Nowcasting — using real-time data to understand conditions as they occur — is one of our best tools. With instruments such as ground-based radar and magnetometers on satellites, <a href="https://doi.org/10.1029/2023GL103733">we can estimate the electromagnetic space weather energy entering the atmosphere almost instantaneously</a>. </p>
<p>As for why SpaceX lost satellites in February 2022 during a minor geomagnetic storm, that was just a matter of timing. The loss of the satellites, however, is a stunning reminder of the power of the universe we live in.</p><img src="https://counter.theconversation.com/content/209955/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Daniel Billett receives funding from the European Space Agency and the Natural Sciences and Engineering Research Council of Canada. </span></em></p>We’re currently a few years into the 25th studied solar cycle. An 11-year period of sun activity, this solar cycle is more active than previously expected.Daniel Billett, Postdoctoral Fellow in Space Physics, University of SaskatchewanLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2042762023-06-19T02:38:10Z2023-06-19T02:38:10ZWhere was the Sun? Here’s why astronomers are more useful in court cases than you’d think<figure><img src="https://images.theconversation.com/files/532540/original/file-20230619-6257-v67z8o.jpg?ixlib=rb-1.1.0&rect=0%2C860%2C3019%2C2091&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://unsplash.com/photos/ZwW1ouTbv6U">Obed Hernández/Unsplash</a></span></figcaption></figure><p>Over the past eight years, I have been asked to submit astronomical evidence for court cases all over Australia.</p>
<p>Normally when we think of evidence in court, we think of eyewitnesses, <a href="https://theconversation.com/dna-is-often-used-in-solving-crimes-but-how-does-dna-profiling-actually-work-191937">DNA</a> or police reports. Often, this evidence requires an expert to explain it – to be able to communicate the findings and data to the members of the court to make an informed decision. These experts are typically in medicine, engineering, psychology, or other fields.</p>
<p>Expert astronomers usually are not what one pictures in court, but that is exactly what I do.</p>
<p>The first time I was asked by police to do it came as a bit of a surprise. I had never thought about applying astronomy to the courtroom. Once the first group knew I can do it, more and more requests came in, from colleagues in the same police force or division, or investigators having seen my evidence elsewhere.</p>
<p>Now, I’m asked to submit evidence for roughly 1–2 cases per week. Usually this requires submitting a <a href="https://www.cornwalls.com.au/your-words-have-power-expert-evidence-and-witness-statements/">statement of evidence</a> to the court. But sometimes I am asked to attend court and explain what the evidence means.</p>
<p>When I’m needed as an expert in court, it tends to be for matters of consequence. My evidence is either critical to a part of the case, or the case itself is fairly major and all the details are being checked and verified.</p>
<p>But what exactly am I providing evidence for?</p>
<h2>Tracking the Sun and the Moon</h2>
<p>Most court evidence from an astronomer involves calculating the positions and lighting from an astronomical body – the Sun or Moon. Luckily, the <a href="https://gml.noaa.gov/grad/solcalc/azel.html">tools we use</a> to calculate the positions of celestial bodies are very accurate, and can be calculated hundreds to thousands of years into the past or future.</p>
<p>An obvious example is when someone claims the Sun was in their eyes, causing a glare, and they get into a car accident. Someone needs to say where the Sun was, its position, and how it aligned with the street and direction of travel. At certain times and in certain directions, the Sun may indeed hinder someone’s vision.</p>
<p>There is also the situation where someone sees something, but it happened around sunrise or sunset. An expert is needed to say what the lighting level was – as there are very clear definitions based on the Sun’s position below the horizon, and how much you can see. For instance, what if the event occurred five minutes after sunset? The light level depends on the time of year, the location and other factors. It is not a clear-cut case of daytime versus nighttime.</p>
<p>The Moon can feature in court evidence as well. Especially in dark locations away from city lights, an astronomer can provide evidence on how much light the Moon provided on a given night.</p>
<p>There are also historical cases or times when people note the view or phase of the Moon as a way of defining when something happened. The full Moon has a precise definition, but the day before or after may appear to look like a full Moon, despite it not technically being full.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/532543/original/file-20230619-15-4m89at.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A photo of a gibbous moon on a black background" src="https://images.theconversation.com/files/532543/original/file-20230619-15-4m89at.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/532543/original/file-20230619-15-4m89at.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=337&fit=crop&dpr=1 600w, https://images.theconversation.com/files/532543/original/file-20230619-15-4m89at.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=337&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/532543/original/file-20230619-15-4m89at.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=337&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/532543/original/file-20230619-15-4m89at.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/532543/original/file-20230619-15-4m89at.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/532543/original/file-20230619-15-4m89at.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Gibbous, full, waning? Astronomers can define the phases of the Moon with greater precision, which can be useful in a court case.</span>
<span class="attribution"><a class="source" href="https://unsplash.com/photos/b_pRpgLvcF8">Patrick Ilao/Unsplash</a></span>
</figcaption>
</figure>
<h2>The limitations of expertise</h2>
<p>Of course, like any part of science, there are limits to what I can say. If someone was looking through a window – how refractive was the window? Were there clouds blocking the Moon or Sun? It is up to other experts, and other parts of the legal system to sort out these factors.</p>
<p>Just like many fields, space technology is changing, and so too is its impact on law and crime. Satellites are being used more and more in cases to help track things as they happen. For example, <a href="https://www.maxar.com/">the space technology company Maxar</a> operates some of the highest-resolution commercial satellites to image Earth. For a small cost, people can task these satellites to look at certain areas and/or times. </p>
<p>Lately, we have seen the impact of satellites on Russia’s war in Ukraine, and how they have been instrumental in looking at troop movements, and even evidence of some of the alleged war crimes.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/ukraine-war-offensive-use-of-satellite-tech-a-sign-of-how-conflict-is-increasingly-moving-into-space-207641">Ukraine war: offensive use of satellite tech a sign of how conflict is increasingly moving into space</a>
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<p>Satellite images have been used for a range of criminal investigations, such as <a href="https://blog.maxar.com/earth-intelligence/2018/the-power-of-a-human-network-reflecting-on-500-geohive-campaigns">people smuggling</a> or <a href="https://blog.maxar.com/earth-intelligence/2022/combating-illegal-gold-mining-in-the-amazon-rainforest-with-maxars-high-resolution-satellite-imagery">illegal mines</a>.</p>
<p>They are also being used in Australia for criminal matters. This is yet another situation where an expert is needed to explain the satellite imagery and what it may mean, or even help access it altogether.</p>
<h2>Experts are vital</h2>
<p>Working as an expert witness has given me hope, because I see the extent to which the justice system will sometimes go to get all the details right – like taking into account the phase of the Moon or the position of the Sun. It is also the perfect example of the importance of experts in our society.</p>
<p>In science, we are actively encouraging people to go to sources of accurate and trustworthy information, especially in an era of rife misinformation.</p>
<p>Through experts, fields like space and astronomy can impact people’s lives directly – even in the court room.</p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/servant-or-partner-the-role-of-expertise-and-knowledge-in-democracy-92026">Servant or partner? The role of expertise and knowledge in democracy</a>
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<img src="https://counter.theconversation.com/content/204276/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Brad E Tucker does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Among the expert witnesses in our justice system, astronomers play a surprising role. This astronomer provides evidence to several cases per week.Brad E Tucker, Astrophysicist, Australian National UniversityLicensed as Creative Commons – attribution, no derivatives.