tag:theconversation.com,2011:/ca/topics/star-32439/articlesStar – The Conversation2024-03-29T12:46:01Ztag:theconversation.com,2011:article/2247202024-03-29T12:46:01Z2024-03-29T12:46:01ZExploding stars are rare but emit torrents of radiation − if one happened close enough to Earth, it could threaten life on the planet<figure><img src="https://images.theconversation.com/files/584272/original/file-20240326-16-h4n3zh.jpg?ixlib=rb-1.1.0&rect=0%2C20%2C3433%2C3972&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Massive dying stars emit large amounts of radiation. </span> <span class="attribution"><a class="source" href="https://newsroom.ap.org/detail/HubbleSpaceTelescopePhotoGallery/e1151b05688d4689bb32d2f46a350506/photo?Query=supernova&mediaType=photo&sortBy=&dateRange=Anytime&totalCount=396&digitizationType=Digitized&currentItemNo=6&vs=true&vs=true">NASA/ESA/Hubble SM4 ERO Team via AP</a></span></figcaption></figure><p>Stars like the Sun are <a href="https://science.nasa.gov/science-research/planetary-science/08jan_sunclimate/">remarkably constant</a>. They vary in brightness by only 0.1% over years and decades, thanks to the fusion of hydrogen into helium that powers them. This process will keep the Sun shining steadily for <a href="https://theconversation.com/the-sun-wont-die-for-5-billion-years-so-why-do-humans-have-only-1-billion-years-left-on-earth-37379">about 5 billion more years</a>, but when stars exhaust their nuclear fuel, their deaths can <a href="https://spaceplace.nasa.gov/supernova/en/">lead to pyrotechnics</a>. </p>
<p><a href="https://www.space.com/14732-sun-burns-star-death.html">The Sun will eventually die</a> by growing large and then condensing into a type of star called a <a href="https://imagine.gsfc.nasa.gov/science/objects/dwarfs2.html">white dwarf</a>. But stars more than eight times more massive than the Sun <a href="https://www.uwa.edu.au/science/-/media/Faculties/Science/Docs/Death-of-a-star.pdf">die violently</a> in an explosion <a href="https://www.space.com/6638-supernova.html">called a supernova</a>. </p>
<p>Supernovae happen across the Milky Way only a <a href="https://www.esa.int/Science_Exploration/Space_Science/Integral/Integral_identifies_supernova_rate_for_Milky_Way">few times a century</a>, and these violent explosions are usually remote enough that people here on Earth don’t notice. For a dying star to have any effect on life on our planet, it would have to go supernova within 100 light years from Earth.</p>
<p>I’m an <a href="https://scholar.google.com/citations?user=OrRLRQ4AAAAJ&hl=en">astronomer</a> who studies <a href="https://wwnorton.com/books/9780393343861">cosmology</a> and <a href="https://wwnorton.com/books/9780393357509">black holes</a>. </p>
<p>In my writing about <a href="https://wwnorton.com/books/9780393339987">cosmic endings</a>, I’ve described the threat posed by <a href="https://warwick.ac.uk/fac/sci/physics/research/astro/outreach/biggestbangs/">stellar cataclysms</a> such as supernovae and related phenomena such as gamma-ray bursts. Most of these cataclysms are remote, but when they occur closer to home they can pose a threat to life on Earth.</p>
<h2>The death of a massive star</h2>
<p>Very few stars are massive enough to die in a supernova. But when one does, it briefly <a href="https://www.sciencedirect.com/topics/physics-and-astronomy/type-ia-supernovae">rivals the brightness of billions of stars</a>. At one supernova per 50 years, and with <a href="https://www.space.com/25303-how-many-galaxies-are-in-the-universe.html">100 billion galaxies in the universe</a>, somewhere in the universe a supernova explodes every hundredth of a second.</p>
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<figcaption><span class="caption">An animation showing a supernova.</span></figcaption>
</figure>
<p>The dying star emits high energy radiation as gamma rays. <a href="https://www.livescience.com/50215-gamma-rays.html">Gamma rays</a> are a form of electromagnetic radiation with wavelengths much shorter than light waves, meaning they’re invisible to the human eye. The dying star also releases a torrent of high-energy particles in the form of <a href="https://news.uchicago.edu/explainer/what-are-cosmic-rays">cosmic rays</a>: subatomic particles moving at close to the speed of light.</p>
<p>Supernovae in the Milky Way are rare, but a few have been close enough to Earth that historical records discuss them. In <a href="https://doi.org/10.1088/1009-9271/6/5/17">185 A.D.</a>, a star appeared in a place where no star had previously been seen. It was probably a supernova. </p>
<p>Observers around the world saw a bright star suddenly appear in <a href="https://noirlab.edu/public/news/noao0305/">1006 A.D</a>. Astronomers later matched it to a supernova 7,200 light years away. Then, in <a href="https://www.wired.com/2012/07/july-4-1054-crab-nebula-makes-a-spectacular-debut-in-the-heavens/">1054 A.D.</a>, Chinese astronomers recorded a star visible in the daytime sky that astronomers subsequently identified as a supernova 6,500 light years away.</p>
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<a href="https://images.theconversation.com/files/584276/original/file-20240326-18-r7dpu3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A man with dark hair and a beard, wearing dark clothes with an elaborate collar, resting one hand on his hip and another on a globe." src="https://images.theconversation.com/files/584276/original/file-20240326-18-r7dpu3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/584276/original/file-20240326-18-r7dpu3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=861&fit=crop&dpr=1 600w, https://images.theconversation.com/files/584276/original/file-20240326-18-r7dpu3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=861&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/584276/original/file-20240326-18-r7dpu3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=861&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/584276/original/file-20240326-18-r7dpu3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1082&fit=crop&dpr=1 754w, https://images.theconversation.com/files/584276/original/file-20240326-18-r7dpu3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1082&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/584276/original/file-20240326-18-r7dpu3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1082&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Johannes Kepler, the astronomer who observed what was likely a supernova in 1604.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:JKepler.jpg">Kepler-Museum in Weil der Stadt</a></span>
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<p><a href="https://www.jpl.nasa.gov/news/the-history-of-johannes-kepler">Johannes Kepler observed</a> the last supernova in the Milky Way in 1604, so in a statistical sense, <a href="https://www.smithsonianmag.com/science-nature/when-will-the-next-supernova-in-our-galaxy-occur-180980422/">the next one is overdue</a>. </p>
<p>At 600 light years away, <a href="https://www.huffpost.com/entry/the-betelgeuse-supernova_b_6583546">the red supergiant Betelgeuse</a> in the constellation of Orion is the nearest massive star getting close to the end of its life. When it goes supernova, it will shine as bright as the full Moon for those watching from Earth, without causing any damage to life on our planet.</p>
<h2>Radiation damage</h2>
<p>If a star goes supernova close enough to Earth, the gamma-ray radiation could damage some of the planetary protection that allows life to thrive on Earth. There’s a time delay due to the finite speed of light. If a supernova goes off 100 light years away, it takes 100 years for us to see it.</p>
<p>Astronomers have found evidence of a supernova 300 light years away that exploded 2.5 million years ago. Radioactive atoms trapped in seafloor sediments are the <a href="https://www.science.org/content/article/exploding-stars-may-have-assaulted-ancient-earth">telltale signs of this event</a>. Radiation from gamma rays eroded the <a href="https://education.nationalgeographic.org/resource/ozone-layer/">ozone layer</a>, which protects life on Earth from the Sun’s harmful radiation. This event would have cooled the climate, leading to the extinction of some ancient species.</p>
<p>Safety from a supernova comes with greater distance. Gamma rays and cosmic rays spread out in all directions once emitted from a supernova, so the fraction that reach the Earth <a href="http://hyperphysics.phy-astr.gsu.edu/hbase/Forces/isq.html">decreases with greater distance</a>. For example, imagine two identical supernovae, with one 10 times closer to Earth than the other. Earth would receive radiation that’s about a hundred times stronger from the closer event.</p>
<p>A supernova within 30 light years would be catastrophic, severely depleting the ozone layer, disrupting the marine food chain and likely causing mass extinction. Some astronomers guess that nearby supernovae triggered a <a href="https://doi.org/10.1073/pnas.2013774117">series of mass extinctions</a> 360 to 375 million years ago. Luckily, these events happen within 30 light years only every few hundred million years. </p>
<h2>When neutron stars collide</h2>
<p>But supernovae aren’t the only events that emit gamma rays. <a href="https://theconversation.com/why-astrophysicists-are-over-the-moon-about-observing-merging-neutron-stars-84957">Neutron star collisions</a> cause high-energy phenomena ranging from gamma rays to <a href="https://www.npr.org/sections/thetwo-way/2017/10/16/557557544/astronomers-strike-gravitational-gold-in-colliding-neutron-stars">gravitational waves</a>. </p>
<p>Left behind after a supernova explosion, <a href="https://www.energy.gov/science/doe-explainsneutron-stars">neutron stars</a> are city-size balls of matter with the density of an atomic nucleus, so 300 trillion times denser than the Sun. These collisions created many of the <a href="https://www.space.com/neutron-star-collisions-gave-earth-precious-metals">gold and precious metals</a> on Earth. The intense pressure caused by two ultradense <a href="https://theconversation.com/cosmic-alchemy-colliding-neutron-stars-show-us-how-the-universe-creates-gold-86104">objects colliding forces neutrons</a> into atomic nuclei, which creates heavier elements such as gold and platinum. </p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/y8VDwGi0r0E?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Neutron stars merge when gravity pulls them together, which releases intense radiation.</span></figcaption>
</figure>
<p>A neutron star collision generates an intense <a href="https://science.nasa.gov/universe/gamma-ray-bursts-harvesting-knowledge-from-the-universes-most-powerful-explosions/">burst of gamma rays</a>. These gamma rays are concentrated into a <a href="https://www.nasa.gov/image-article/neutron-stars-collide/">narrow jet</a> of radiation that packs a big punch. </p>
<p>If the Earth were in the line of fire of a gamma-ray burst within <a href="https://www.aps.org/publications/apsnews/200407/extinction.cfm">10,000 light years</a>, or 10% of the diameter of the galaxy, the burst would <a href="https://doi.org/10.1086/496914">severely damage the ozone layer</a>. It would also damage the DNA inside organisms’ cells, at a level that would kill many simple life forms like bacteria.</p>
<p>That sounds ominous, but neutron stars do not typically form in pairs, so there is <a href="https://journals.aps.org/prx/abstract/10.1103/PhysRevX.13.011048">only one collision in the Milky Way about every 10,000 years</a>. They are <a href="https://www.scientificamerican.com/article/a-nearby-neutron-star-collision-could-cause-calamity-on-earth/">100 times rarer than supernova explosions</a>. Across the entire universe, there is a neutron star collision every few minutes.</p>
<p>Gamma-ray bursts may not hold an imminent threat to life on Earth, but over very long time scales, bursts will inevitably hit the Earth. The <a href="https://www.livescience.com/49040-gamma-ray-burst-mass-extinction.html">odds of a gamma-ray burst triggering a mass extinction</a> are 50% in the past 500 million years and 90% in the 4 billion years since there has been life on Earth. </p>
<p>By that math, it’s quite likely that a gamma-ray burst caused one of the <a href="https://ourworldindata.org/mass-extinctions">five mass extinctions</a> in the past 500 million years. Astronomers have argued that a gamma-ray burst caused the <a href="https://doi.org/10.1017/S1473550404001910">first mass extinction</a> 440 million years ago, when <a href="https://ucmp.berkeley.edu/ordovician/ordovician.html">60% of all marine creatures disappeared</a>.</p>
<h2>A recent reminder</h2>
<p>The most extreme astrophysical events have a long reach. Astronomers were reminded of this in October 2022, when a pulse of radiation swept through the solar system and overloaded all of the gamma-ray telescopes in space.</p>
<p>It was the <a href="https://www.nasa.gov/universe/nasa-missions-study-what-may-be-a-1-in-10000-year-gamma-ray-burst/">brightest gamma-ray burst</a> to occur since human civilization began. The radiation caused a sudden disturbance <a href="https://www.swpc.noaa.gov/phenomena/ionosphere">to the Earth’s ionosphere</a>, even though the source was an explosion nearly <a href="https://www.science.org/content/article/cosmic-blast-seared-earth-s-atmosphere-2-billion-light-years-away">2 billion light years away</a>. Life on Earth was unaffected, but the fact that it altered the ionosphere is sobering – a similar burst in the Milky Way would be a million times brighter.</p><img src="https://counter.theconversation.com/content/224720/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Chris Impey receives funding from the National Science Foundation and the Howard Hughes Medical Institute.</span></em></p>Some ancient texts record what were likely dying stars, faintly visible from Earth. If close enough, these events can disturb telescopes and even damage the ozone layer.Chris Impey, University Distinguished Professor of Astronomy, University of ArizonaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2172412023-12-18T13:23:27Z2023-12-18T13:23:27ZWhy are some black holes bigger than others? An astronomer explains how these celestial vacuums grow<figure><img src="https://images.theconversation.com/files/562536/original/file-20231129-23-ug9ynd.jpg?ixlib=rb-1.1.0&rect=5%2C15%2C3429%2C2863&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Black holes use gravity to pull matter into them. </span> <span class="attribution"><a class="source" href="https://newsroom.ap.org/detail/HungryBlackHole/4cd9b7c1c318427ba2f3b78c77cfe6de/photo?Query=black%20hole&mediaType=photo&sortBy=&dateRange=Anytime&totalCount=418&currentItemNo=7&vs=true&vs=true">NASA/Chandra X-ray Observatory/M.Weiss via AP</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><strong>Why are there small and big black holes? Also, why are some black holes invisible and others have white outlines? – Sedra and Humaid, Abu Dhabi, United Arab Emirates</strong></p>
</blockquote>
<hr>
<p><a href="https://theconversation.com/the-scariest-things-in-the-universe-are-black-holes-and-here-are-3-reasons-148615">Black holes</a> are dense astronomical objects with gravity so strong that nothing, not even light, can escape. Anything that crosses the boundary of a black hole’s gravitational influence, called the event horizon, will fall into the black hole. Inside this deep, dense pit, it is never to be seen again. </p>
<p>Black holes litter the universe. Some smaller black holes are sprinkled randomly throughout galaxies like our Milky Way. Other gigantic ones, called <a href="https://theconversation.com/supermassive-black-hole-at-the-center-of-our-galaxy-may-have-a-friend-128295">“supermassive” black holes</a>, lie at the centers of galaxies. Those can weigh anywhere between a million to a billion times the mass of our Sun. So you might be wondering: How can astronomers possibly see something so dark and so big?</p>
<p>I am an <a href="https://jackiechampagne.com">astronomer</a> who studies the very first supermassive black holes that formed in our universe. I want to understand how black holes form and what kinds of astrophysical neighborhoods they grow up in.</p>
<h2>Types of black holes</h2>
<p>Let’s talk about how black holes begin their lives. Two famous scientists, <a href="https://www.britannica.com/biography/Albert-Einstein">Albert Einstein</a> and <a href="https://www.britannica.com/biography/Karl-Schwarzschild">Karl Schwarzchild</a>, first pitched the <a href="https://www.astronomy.com/science/a-brief-history-of-black-holes/">idea of a black hole</a>. They thought that when a large star dies, its core might shrink and shrink until it <a href="https://universe.nasa.gov/black-holes/types/">collapses under its own weight</a>. This is what we astronomers call a “<a href="https://www.nasa.gov/image-article/stellar-mass-black-hole/">stellar mass black hole</a>,” which is just another way of saying it’s comparatively very small.</p>
<p>Stellar mass black holes are only a few times bigger than our Sun. Supermassive black holes are more of a mystery, though. They are many millions of times heavier than our Sun, and they are packed into a small area that’s about the size of our solar system. Some scientists think supermassive black holes might form by <a href="https://science.nasa.gov/astrophysics/focus-areas/black-holes/">many stars colliding and collapsing at once</a>, while others think they might have already started growing several billion years ago. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/tMax0KgyZZU?wmode=transparent&start=13" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Stars at the center of the Milky Way are orbiting around an invisible object, a supermassive black hole, like planets orbit around the Sun. Credit: Andrea Ghez/UCLA/W.M. Keck Observatory.</span></figcaption>
</figure>
<h2>Growing black holes</h2>
<p>What do black holes look like? Most of the time, they are not actively growing, so they are invisible. But we can tell they’re there because <a href="https://theconversation.com/2020-nobel-prize-in-physics-awarded-for-work-on-black-holes-an-astrophysicist-explains-the-trailblazing-discoveries-147614">stars can still orbit around them</a>, just like Earth around the Sun. </p>
<p>When something is orbiting an invisible object at high speeds, scientists know there <a href="https://theconversation.com/2020-nobel-prize-in-physics-awarded-for-work-on-black-holes-an-astrophysicist-explains-the-trailblazing-discoveries-147614">must be a massive black hole</a> in the middle. This is the case for the closest supermassive black hole to us, which lies at the center of the Milky Way – safely millions of miles away from you.</p>
<p>Meanwhile, when a hungry black hole is eating up gas in a galaxy, it heats that gas up until you can see a <a href="https://universe.nasa.gov/black-holes/anatomy/">glowing ring</a> of X-rays, optical light and infrared light around the black hole. Once it exhausts all of the fuel near the event horizon, the light dies down once again and it becomes invisible. </p>
<h2>Outlines around black holes</h2>
<p>One of the most famous “white outlines” is the <a href="https://cerncourier.com/a/building-gargantua/">image of a black hole</a> from <a href="https://www.imdb.com/title/tt0816692/">the movie “Interstellar</a>.” In that movie, they were trying to show the white-hot, glowing ring of gases that are falling into the actively growing black hole. </p>
<p>In real life, we don’t get such a close-up view. The best image of the ring around a real black hole comes from the <a href="https://eventhorizontelescope.org/">Event Horizon Telescope</a>, showing scientists the supermassive black hole at the center of a <a href="https://science.nasa.gov/resource/first-image-of-a-black-hole/">galaxy called M87</a>. It might look blurry to you, but this doughnut is actually the sharpest image ever taken of something so far away.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/559440/original/file-20231114-27-fnfqnq.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A blurry golden circle against a black background." src="https://images.theconversation.com/files/559440/original/file-20231114-27-fnfqnq.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/559440/original/file-20231114-27-fnfqnq.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=350&fit=crop&dpr=1 600w, https://images.theconversation.com/files/559440/original/file-20231114-27-fnfqnq.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=350&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/559440/original/file-20231114-27-fnfqnq.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=350&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/559440/original/file-20231114-27-fnfqnq.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=439&fit=crop&dpr=1 754w, https://images.theconversation.com/files/559440/original/file-20231114-27-fnfqnq.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=439&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/559440/original/file-20231114-27-fnfqnq.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=439&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 first-ever image of a black hole was taken by the Event Horizon Telescope in 2019. You can see the light as it bends around the intense gravity of the black hole at the center of a galaxy called M87. It might look blurry, but this is the equivalent of being able to read a newspaper on a table in Paris if you were standing in New York.</span>
<span class="attribution"><a class="source" href="https://eventhorizontelescope.org/press-release-april-10-2019-astronomers-capture-first-image-black-hole">Event Horizon Telescope</a></span>
</figcaption>
</figure>
<p>There are lots of types of black holes out there in the universe. Some are small and invisible, and some grow to gigantic proportions by eating up stuff inside a galaxy and shining bright. But don’t worry, black holes can’t just keep sucking in everything in the universe – eventually there is nothing close enough to the black hole to fall in, and it will become invisible again. So you are safe to keep asking questions about black holes. </p>
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<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/217241/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jaclyn Champagne receives funding from the National Science Foundation and the Space Telescope Science Institute. </span></em></p>Pictures of black holes have a white outline around them when photographed, due to one of black holes’ unique and key features.Jaclyn Champagne, JASPER Postdoctoral Researcher, University of ArizonaLicensed 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/1980352023-02-09T16:59:27Z2023-02-09T16:59:27ZLight pollution has cut humanity’s ancient connection with the stars – but we can restore it<figure><img src="https://images.theconversation.com/files/508340/original/file-20230206-31-b29opi.jpg?ixlib=rb-1.1.0&rect=4%2C0%2C2991%2C1994&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/milky-way-rises-over-pine-trees-384983128">Andrey Prokhorov/Shutterstock</a></span></figcaption></figure><p>Humans are naturally afraid of the dark. We sometimes imagine monsters under the bed and walk faster down unlit streets at night. To conquer our fears, we may leave a night light on to scare away the monsters and a light over the porch to deter break-ins. </p>
<p>Yet, in huddling for safety under our pools of light, we have lost our connection to the night sky. Star counts by public awareness campaign <a href="https://www.globeatnight.org/">Globe at Night</a> revealed that, between 2011 and 2022, the world’s night sky <a href="https://www.theguardian.com/environment/2023/jan/19/light-pollution-rapidly-reducing-stars-visible-naked-eye-study-finds">more than doubled in artificial brightness</a>. Yet local interventions can create meaningful change. </p>
<p>Light pollution is cutting us off from one of nature’s greatest wonders, harming wildlife and blocking research that could help fight climate change. Stars are more than pretty glimmers in the night sky. They have shaped the mythology of every human civilisation. They guide birds on their astonishing migratory journeys. And now we need to do our bit to prevent light pollution so stars can be part of our future. </p>
<p><a href="https://skyandtelescope.org/astronomy-blogs/how-many-stars-night-sky-09172014/">The human eye can detect around 5,000</a> stars in the night sky. But the light emitted by skyscrapers, street lamps, and houses obscures all but a handful of the brightest stars. </p>
<p>Our ancestors used the rising and setting of the constellations as <a href="https://www.britannica.com/science/calendar/Time-determination-by-stars-Sun-and-Moon">calendars</a>. They also <a href="https://theconversation.com/how-far-theyll-go-moana-shows-the-power-of-polynesian-celestial-navigation-72375#:%7E:text=The%20position%20of%20Moana's%20hand,are%20travelling%20exactly%20due%20East.&text=Later%20in%20the%20film%2C%20we,by%20following%20Maui's%20fish%20hook.">navigated by the stars</a> as they searched for new lands or traced nautical trade routes. Sailors don’t normally use the stars to navigate any more, but they are still taught how to, <a href="https://www.popularmechanics.com/military/research/a36078957/celestial-navigation/">in case their navigation systems break down</a>. </p>
<p>Migratory animals, including birds and insects, are <a href="https://www.darksky.org/light-pollution/wildlife/">drawn away from their natural flight paths</a> by the beckoning “sky glow” of cities. In the summer of 2019, Las Vegas was <a href="https://www.smithsonianmag.com/smart-news/las-vegas-was-inundated-46-million-grasshoppers-single-night-2019-180977395/">invaded</a> by millions of migrating grasshoppers, while the beams of New York’s <a href="https://www.nytimes.com/2018/09/10/opinion/9-11-tribute-in-light-birds.html">9/11 Tribute in Light</a> are a magnet for flocks of migrating songbirds flying at night. </p>
<p>Disoriented by the bright city lights, birds crash into towering skyscrapers. Insect numbers are collapsing worldwide and light pollution is making matters worse by <a href="https://www.smithsonianmag.com/smart-news/light-pollution-contributes-insect-apocalypse-180973642/">disrupting their nocturnal life cycles</a>.</p>
<h2>What is light pollution</h2>
<p>Light pollution is caused by the same <a href="https://spaceplace.nasa.gov/blue-sky/en/">physics that turns the sky blue during the day</a>. Sunlight is made up of all the colours of the rainbow and each colour has a different wavelength. The air that surrounds us is composed of tiny particles (such as oxygen and carbon dioxide molecules). </p>
<p>As light from the Sun makes its way through the air, it is scattered by these particles in random directions. Blue light (with shorter wavelengths) is scattered more than red light (which has longer wavelengths). As a result, our eyes receive more blue light from every direction in the sky. </p>
<p>At night, light scattered by the same air particles causes the sky to shine down on us. A small fraction of this sky glow is caused by natural sources, such as starlight and the Earth’s atmosphere. But most of the light that creates sky glow is artificial. </p>
<figure class="align-center ">
<img alt="The constellation Orion, imaged at left from dark skies, and at right from the teeming metropolis of Orem, UT comprising about half a million people." src="https://images.theconversation.com/files/509173/original/file-20230209-22-xf5oal.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/509173/original/file-20230209-22-xf5oal.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=440&fit=crop&dpr=1 600w, https://images.theconversation.com/files/509173/original/file-20230209-22-xf5oal.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=440&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/509173/original/file-20230209-22-xf5oal.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=440&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/509173/original/file-20230209-22-xf5oal.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=553&fit=crop&dpr=1 754w, https://images.theconversation.com/files/509173/original/file-20230209-22-xf5oal.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=553&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/509173/original/file-20230209-22-xf5oal.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">
<figcaption>
<span class="caption">Light pollution is not pretty.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Light_pollution_It%27s_not_pretty.jpg">Jeremy Stanley/Wikimedia</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Light pollution also affects our ability to study the universe. Even modern observatories, built on remote mountaintops, are affected by the encroaching sky glow from growing, sprawling cities. Light pollution is so widespread that <a href="https://www.space.com/major-observatories-suffering-light-pollution">three quarters of all observatories</a> are affected. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/h0RKQmVAeQM?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Migrating birds flying through Tribute in Light in 2015.</span></figcaption>
</figure>
<h2>Looking up</h2>
<p>There is no reason to despair, though. We created light pollution; we can fix it.</p>
<p>Around the world, <a href="https://www.darksky.org/">dark sky</a> <a href="https://www.darkskydiscovery.org.uk/">associations</a> are working to educate the public about the hazards of light pollution, to lobby for <a href="https://www.allaboutbirds.org/news/new-york-city-passes-landmark-lights-out-laws/">legislation to protect dark sky reserves</a> and encourage people to reignite their connection with <a href="https://www.darksky.org/our-work/lighting/">dark, star-studded skies</a>.</p>
<p><a href="https://theconversation.com/turn-off-the-porch-light-6-easy-ways-to-stop-light-pollution-from-harming-our-wildlife-132595">Fighting light pollution begins at home.</a> If you need to keep outside lights on for security, use shielded lamps that only shine downwards. Use light bulbs that do not emit violet and blue light as this is harmful to wildlife. Smart lighting controls will also help reduce your house’s effect on wildlife and make it easier for you to observe the night sky.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/505372/original/file-20230119-16-5t6mrz.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/505372/original/file-20230119-16-5t6mrz.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=267&fit=crop&dpr=1 600w, https://images.theconversation.com/files/505372/original/file-20230119-16-5t6mrz.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=267&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/505372/original/file-20230119-16-5t6mrz.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=267&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/505372/original/file-20230119-16-5t6mrz.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=336&fit=crop&dpr=1 754w, https://images.theconversation.com/files/505372/original/file-20230119-16-5t6mrz.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=336&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/505372/original/file-20230119-16-5t6mrz.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=336&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">2016 world map of artificial sky brightness. 80% of the world’s population is now affected by light pollution. Credit: Falchi et al., Science Advances, 2016;2:e160037.</span>
</figcaption>
</figure>
<p>You will also find <a href="https://www.lightpollutionmap.info">interactive maps</a> that show how polluted the skies are in your area. These maps are created from data gathered by satellites and by citizen scientists taking part in annual star counts. You can help darken our skies, too. </p>
<p>In the UK, the 2023 annual star count will take place on <a href="https://www.cpre.org.uk/what-we-care-about/nature-and-landscapes/dark-skies/star-count-2023/">February 17-24</a>. And, wherever you are in the world, you can always take part in the year-long <a href="https://globeatnight.org/">Globe at Night</a> star count whenever you want. </p>
<p>The task is simple: step outside on a clear night, count how many stars you can see in a well-known constellation, such as Orion, and report back. </p>
<p>To defeat light pollution, we need to know how severe it is and what difference national policies and local interventions (such as replacing the street lights in your town) make. In the UK, for example, star counts show light pollution may have <a href="https://www.cpre.org.uk/news/night-skies-outlook-is-bright-our-star-count-results-suggest/">peaked in 2020</a> and has started to decline. </p>
<p>Perhaps the most important aspect of star counts is that they shine a light on our vanishing night skies and galvanize us to take action. Ultimately, it’s up to each and every one of us to reduce our effect on the sky, by changing the way we light our homes and neighbourhoods and by lobbying our representatives to pass <a href="https://www.allaboutbirds.org/news/new-york-city-passes-landmark-lights-out-laws/#">dark sky legislation</a>. </p>
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<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">
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<p><strong><em>Don’t have time to read about climate change as much as you’d like?</em></strong>
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<hr><img src="https://counter.theconversation.com/content/198035/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Or Graur 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>People travel hundreds or thousands of miles and spend a fortune to see the night sky in all its splendor. But we are literally blocking out the cosmic beauty above our homes.Or Graur, Reader in Astrophysics, University of PortsmouthLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1960522022-12-08T19:24:10Z2022-12-08T19:24:10Z‘Extreme stripping action’ led to the messy birth of the Southern Ring Nebula, Webb image reveals<figure><img src="https://images.theconversation.com/files/499746/original/file-20221208-22-s12rbl.png?ixlib=rb-1.1.0&rect=7%2C71%2C4764%2C3620&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">NASA</span></span></figcaption></figure><p>When the first five images from the James Webb Space Telescope (JWST) were unveiled, one of them stared at me with two eyes. It was an image of the Southern Ring Nebula, NGC3132, and smack in the middle were two bright stars.</p>
<p>Now, the fact that NGC3132 houses a binary star system (two stars orbiting one another) has been known since the days of the Hubble Space Telescope. </p>
<p>But in those early images, the central star that ejected the nebula – a tiny, hot white dwarf – was so dim it was almost invisible next to its bright Sun-like companion. In effect, the nebula had one eye almost closed. </p>
<p>But the JWST reveals more than Hubble did. It can collect “cooler” photons (light particles) in the infrared range of the electromagnetic spectrum. In this cooler light, we saw both stars in the binary system shining as bright as one another: two glaring eyes! </p>
<p>This was surprising to any astronomer who understands this type of nebula; super-hot white dwarfs typically don’t shine brightly in infrared light. It made sense for the cooler star to be shining this way, but observing the same brilliance from its partner was unexpected.</p>
<p>Emails started to bolt coast to coast and across oceans as astronomers pieced the puzzle together. The central white dwarf star of NGC3132, they realised, is enshrouded in dust. The dust is warmed up by the star’s heat and therefore shines in the infrared, producing the light we observed. </p>
<p>It was this that led us on the trail to find out what was really happening in the Southern Ring Nebula. Our findings from a team of nearly 70 astronomers are <a href="https://www.nature.com/articles/s41550-022-01845-2">published today</a> in Nature Astronomy. </p>
<h2>At the heart, a hot white dwarf</h2>
<p>The Southern Ring Nebula is a planetary nebula. That means it’s a gaseous nebula formed by a Sun-like star shedding most of its gas in the last act before its demise. </p>
<p>Once it shed much of its mass, the star became a hot white dwarf. This central star now sits in the middle of the nebula, cooling like a stellar ember, effectively dying. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/499740/original/file-20221208-11-k8glwk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/499740/original/file-20221208-11-k8glwk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/499740/original/file-20221208-11-k8glwk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=534&fit=crop&dpr=1 600w, https://images.theconversation.com/files/499740/original/file-20221208-11-k8glwk.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=534&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/499740/original/file-20221208-11-k8glwk.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=534&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/499740/original/file-20221208-11-k8glwk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=671&fit=crop&dpr=1 754w, https://images.theconversation.com/files/499740/original/file-20221208-11-k8glwk.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=671&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/499740/original/file-20221208-11-k8glwk.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=671&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">You can see the two central stars quite clearly in this image, the dust-enshrouded white dwarf in the red and its companion to its left.</span>
<span class="attribution"><span class="source">NASA</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>The beauty of planetary nebulae is they can be looked at forensically: parts of the nebula farther from the middle were ejected earlier in time. In this way, the entire nebula functions a bit like a geological record.</p>
<p>With its dying white dwarf in the centre, our group approached NGC3132 like a crime scene.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/a-cosmic-time-machine-how-the-james-webb-space-telescope-lets-us-see-the-first-galaxies-in-the-universe-187015">A cosmic time machine: how the James Webb Space Telescope lets us see the first galaxies in the universe</a>
</strong>
</em>
</p>
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<h2>Two unknown suspects emerge</h2>
<p>First, we quickly realised the dust making the central star shine so brightly was actually a disk wrapped closely around the central star that must have been forged by a companion. This orbiting companion star would have stripped gas away from the central star, hastening its demise. </p>
<p>We didn’t spot the companion, though. We think it’s either too faint to detect, or has potentially perished in the interaction and merged with the central star. </p>
<p>Then we noticed something else: broken concentric arches engraved in the extended halo of the nebula. These also betrayed the presence of an orbiting companion. Could this culprit be the same one that forged the disk of dust?</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/499743/original/file-20221208-24-8f4ak2.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/499743/original/file-20221208-24-8f4ak2.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/499743/original/file-20221208-24-8f4ak2.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=591&fit=crop&dpr=1 600w, https://images.theconversation.com/files/499743/original/file-20221208-24-8f4ak2.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=591&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/499743/original/file-20221208-24-8f4ak2.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=591&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/499743/original/file-20221208-24-8f4ak2.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=743&fit=crop&dpr=1 754w, https://images.theconversation.com/files/499743/original/file-20221208-24-8f4ak2.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=743&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/499743/original/file-20221208-24-8f4ak2.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=743&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Note the concentric arches on the edges of the nebula.</span>
<span class="attribution"><span class="source">NASA</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>We don’t think so. Although the arches have suffered some “weathering”, our measurements of them betray the presence of yet another companion star. This one is placed a little too far from the central star to have created the dust disk. </p>
<p>And just like that, we had gathered evidence the Southern Ring Nebula contains not just two stars in a binary system, but four. </p>
<p>And we would gather more yet. </p>
<h2>Tied up in a bumpy, gassy bubble</h2>
<p>The “ring” that gives the nebula its name is actually the wall of an egg-shaped bubble containing hot gas, heated by the central star. This wall is marked with noticeable protuberances.</p>
<p>Combining the JWST image with data from the European Southern Observatory, our team created a 3D model that revealed these protuberances come in pairs, moving in opposite directions away from the central star. </p>
<p>One possible explanation is the interaction that created the dust disk didn’t involve just one close companion, but two. In other words, we’re looking at a potential fifth star in the mix – interacting chaotically with the central star to blow out jets that push out those protuberances.</p>
<p>This fifth star’s presence is still tentative. But we can say with a good degree of certainty the stellar system that created the Southern Ring Nebula comprises not just the binary star system (the two eyes of the nebula), but also a third star that ripped away the gas to form the disk, and another that inscribed a track of concentric arches in the gas bubble. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/499742/original/file-20221208-12-q7hy77.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/499742/original/file-20221208-12-q7hy77.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=325&fit=crop&dpr=1 600w, https://images.theconversation.com/files/499742/original/file-20221208-12-q7hy77.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=325&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/499742/original/file-20221208-12-q7hy77.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=325&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/499742/original/file-20221208-12-q7hy77.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=409&fit=crop&dpr=1 754w, https://images.theconversation.com/files/499742/original/file-20221208-12-q7hy77.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=409&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/499742/original/file-20221208-12-q7hy77.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=409&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The panels above are a time-lapse cartoon of the formation of NGC3132. Star 1 is the central star (shown in the first panel before it becomes a white dwarf). Star 2 is the distant bystander companion. Star 3 and 4 are responsible for emitting jets that created protuberances in the shape of the gas bubble, and form the dusty disk around the white dwarf (shown in panel 4). Star 5 gave rise to the formation of the concentric arches.</span>
<span class="attribution"><span class="source">NASA, ESA, CSA, E. Wheatley (STScI)</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>As for the second eye of the nebula – the one we’d always known about – it was definitely an innocent bystander. It’s too far from the central star to have participated in its demise.</p>
<h2>One case closed, more to come</h2>
<p>The case of the Southern Ring Nebula isn’t the only one demonstrating how stars work in packs. Much of stellar astrophysics is being revisited today in light of the realisation of just how gregarious stars can be. And we’re all the more excited for it. </p>
<p>A wealth of phenomena arise from stellar interactions, from supernova explosions, to the merging of black holes and neutron stars giving rise to gravitational wave events. </p>
<p>As the JWST delivers more detailed images of the universe, astronomers will be keenly dusting off their gloves to tackle more mysteries.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/the-james-webb-space-telescope-has-taken-its-first-aligned-image-of-a-star-heres-how-it-was-done-178315">The James Webb Space Telescope has taken its first aligned image of a star. Here's how it was done</a>
</strong>
</em>
</p>
<hr>
<img src="https://counter.theconversation.com/content/196052/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Orsola De Marco is affiliated with Astronomy Australia Limited (non-executive board director and chair of the board). This is a non-for-profit company that applies for and administers NCRIS grants to Australian Astronomy.</span></em></p>Astronomers have unpacked the mystery of how one star’s death created the nebula NGC3132 – never before seen in such detail.Orsola De Marco, Professor of Astrophysics, Macquarie UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1210752020-01-21T13:49:57Z2020-01-21T13:49:57ZEven planets have their (size) limits<figure><img src="https://images.theconversation.com/files/297273/original/file-20191016-98661-1c4okmk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A planet-forming disk made from rock and gas surrounds a young star. </span> <span class="attribution"><a class="source" href="https://www.jpl.nasa.gov/news/news.php?feature=927">NASA/JPL-Caltech/SwRI/MSSS/ Gerald Eichstädt /Seán Doran</a></span></figcaption></figure><p>Scientists have discovered over 4,000 exoplanets outside of our Solar System, according to <a href="https://exoplanetarchive.ipac.caltech.edu/">NASA’s Exoplanet Archive</a>.</p>
<p>Some of these planets orbit <a href="https://en.wikipedia.org/wiki/Circumbinary_planet">multiple stars</a> at the same time. Certain planets are so close to their star that it takes only a handful of days to make one revolution, compared to the Earth which takes 365.25 days. Others slingshot around their star with <a href="http://www.hzgallery.org/913_2.png">extremely oblong orbits</a>, unlike the Earth’s circular one. When it comes to how exoplanets behave and where they exist, there are many possibilities.</p>
<p>And yet, when it comes to sizes of planets, specifically their mass and radius, there are some limitations. And for that, we have physics to blame.</p>
<p><a href="https://scholar.google.com/citations?user=u6_GYWkAAAAJ&hl=en&oi=ao">I am a planetary astrophysicist</a> and I try to understand what makes a <a href="https://www.youtube.com/watch?v=AKA0z6SOHws">planet able to support life</a>. I look at the chemical <a href="http://www.nataliehinkel.com">connection between stars and their exoplanets</a> and how the interior structure and mineralogy of different sized planets compare to each other. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/310996/original/file-20200120-69539-754k58.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/310996/original/file-20200120-69539-754k58.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/310996/original/file-20200120-69539-754k58.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/310996/original/file-20200120-69539-754k58.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/310996/original/file-20200120-69539-754k58.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/310996/original/file-20200120-69539-754k58.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/310996/original/file-20200120-69539-754k58.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/310996/original/file-20200120-69539-754k58.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">This sketch illustrates a family tree of exoplanets starting from the protoplanetary disk, which is a swirling disk of gas and dust surrounding a planet (much like a stellar disk but smaller). Gas and dust is pulled onto the planet, depending on the planet’s mass and gravity.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/image-feature/ames/new-branch-in-exoplanet-family-tree">NASA/Ames Research Center/JPL-Caltech/Tim Pyle</a></span>
</figcaption>
</figure>
<h2>Rocky versus gaseous planets</h2>
<p>In our Solar System, we have two kinds of planets: small, <a href="https://en.wikipedia.org/wiki/Terrestrial_planet">rocky</a>, dense planets that are similar to Earth and large, <a href="https://en.wikipedia.org/wiki/Gas_giant">gaseous planets</a> like Jupiter. From what we astrophysicists have detected so far, most planets fall into these two categories. </p>
<p>In fact, when we look at the data from planet-hunting missions such as the <a href="https://www.nasa.gov/mission_pages/kepler/overview/index.html">Kepler mission</a> or from the <a href="https://www.nasa.gov/tess-transiting-exoplanet-survey-satellite">Transiting Exoplanet System Satellite</a>, there is a gap in the planet sizes. Namely, there <a href="https://arxiv.org/abs/1703.10375">aren’t many planets that fulfill the definition of a “super-Earth,”</a> with a radius of one and a half to twice Earth’s radius and a mass that is five to 10 times greater.</p>
<p>So the question is, why aren’t there any super-Earths? Why do astronomers only see small rocky planets and enormous gaseous planets?</p>
<p>The differences between the two kinds of planets, and the reason for this super-Earth gap, has everything to do with a planet’s atmosphere – especially when the planet is forming. </p>
<p><a href="https://en.wikipedia.org/wiki/Star_formation">When a star is born</a>, a huge ball of gas comes together, starts to spin, collapses in on itself and ignites a <a href="https://en.wikipedia.org/wiki/Fusion">fusion reaction</a> within the star’s core. This process isn’t perfect; there is a lot of extra gas and dust left over after the star is formed. The extra material continues to rotate around the star until it eventually forms into a stellar disk: a flat, ring-shaped collection of gas, dust, and rocks. </p>
<p>During all of this motion and commotion, the dust grains slam into each other, forming pebbles which then grow into larger and larger boulders until they form planets. As the planet grows in size, its mass and therefore gravity increases, allowing it to capture not only the accumulated dust and rocks – but also the gas, which forms an atmosphere. </p>
<p>There is lots of gas within the stellar disk – after all, hydrogen and helium are the most common elements in stars and in the universe. However, there is considerably less rocky material because only a limited amount was made during star formation.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/310994/original/file-20200120-69543-1yrmgez.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/310994/original/file-20200120-69543-1yrmgez.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/310994/original/file-20200120-69543-1yrmgez.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/310994/original/file-20200120-69543-1yrmgez.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/310994/original/file-20200120-69543-1yrmgez.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/310994/original/file-20200120-69543-1yrmgez.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/310994/original/file-20200120-69543-1yrmgez.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/310994/original/file-20200120-69543-1yrmgez.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">Comparison of confirmed super-Earth planets compared to the size of the Earth.</span>
<span class="attribution"><a class="source" href="https://exoplanets.nasa.gov/news/207/finding-another-earth/">NASA/Ames/JPL-Caltech</a></span>
</figcaption>
</figure>
<h2>The trouble with super-Earths</h2>
<p>If a planet remains relatively small, with a radius less than 1.5 times Earth’s radius, then its gravity is not strong enough to hold onto a huge amount of atmosphere, like what’s on Neptune or Jupiter. If, however, it continues to grow larger, then it captures more and more gas which forms an atmosphere that causes it to swell to the size of Neptune (four times Earth’s radius) or Jupiter, 11 times Earth’s radius. </p>
<p>Therefore, a planet either stays small and rocky, or it becomes a large, gaseous planet. The middle ground, where a super-Earth might be formed, is very difficult because, once it has enough mass and gravitational pull, it needs the exact right circumstances to stop the avalanche of gas from piling onto the planet and puffing it up. This is sometimes referred to as “unstable equilibrium” – such that when a body (or a planet) is slightly displaced (a little bit more gas is added) it departs further from the original position (and becomes a giant planet).</p>
<p>Another factor to consider is that once a planet is formed, it doesn’t always stay in the same orbit. Sometimes planets move or migrate towards their host star. As the planet gets closer to the star, its atmosphere heats up causing the atoms and molecules to move very fast and escape the planet’s gravitational pull. So some of the small rocky planets are actually the cores of <a href="https://arxiv.org/pdf/1706.02050.pdf">bigger planets that have been stripped of their atmosphere</a>. </p>
<p>So, while there are no super huge rocky planets or small fluffy planets, there is still a huge amount of diversity in planet sizes, geometries and compositions. </p>
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<p class="fine-print"><em><span>Natalie Hinkel receives funding from the NASA Nexus for Exoplanet System Science research coordination network based out of Arizona State University. This funding is used to research exoplanet habitability.</span></em></p>Why isn’t there an endless variety of planets in the universe? An astrophysicist explains why planets only come in two flavors.Natalie Hinkel, Planetary Astrophysicist, Senior Research Scientist at the Southwest Research Institute and Co-Investigator for the Nexus for Exoplanet System Science (NExSS), Arizona State UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1241582019-12-16T13:43:04Z2019-12-16T13:43:04ZPlanetary confusion – why astronomers keep changing what it means to be a planet<figure><img src="https://images.theconversation.com/files/300167/original/file-20191104-88409-13vd5ta.png?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">In 2015, NASA’s New Horizons spacecraft looked back toward the sun and captured this near-sunset view of the rugged, icy mountains and flat ice plains extending to Pluto’s horizon. </span> <span class="attribution"><a class="source" href="https://www.nasa.gov/image-feature/pluto-s-majestic-mountains-frozen-plains-and-foggy-hazes">NASA/JHUAPL/SwRI</a></span></figcaption></figure><p>As an astronomer, the question I hear the most is why isn’t Pluto a planet anymore? More than 10 years ago, astronomers famously voted to change <a href="https://www.nytimes.com/2006/08/24/science/space/25pluto.html">Pluto’s classification</a>. But the question still comes up. </p>
<p>When I am asked directly if I think Pluto is a planet, I tell everyone my answer is no. It all goes back to the origin of the word “planet.” It comes from the Greek phrase for “wandering stars.” Back in ancient times before the telescope was invented, the mathematician and astronomer Claudius Ptolemy called stars “fixed stars” to distinguish them from the seven wanderers that move across the sky in a very specific way. <a href="https://www.loc.gov/collections/finding-our-place-in-the-cosmos-with-carl-sagan/articles-and-essays/modeling-the-cosmos/ancient-greek-astronomy-and-cosmology">These seven objects are the Sun, the Moon, Mercury, Venus, Mars, Jupiter and Saturn</a>.</p>
<p>When people started using the word “planet,” they were referring to those seven objects. Even Earth was not originally called a planet – but the Sun and Moon were. </p>
<p>Since people use the word “planet” today to refer to many objects beyond the original seven, it’s no surprise we argue about some of them.</p>
<p>Although I am trained as an astronomer and I studied more distant objects like stars and galaxies, I have an interest in the objects in our Solar System because I teach several classes on planetary science.</p>
<h2>Asteroids, the first demoted planets</h2>
<p>The word “planet” is used to describe <a href="https://www.skyandtelescope.com/observing/ice-giants-neptune-and-uranus/">Uranus and Neptune</a>, which were discovered in 1781 and 1846 respectively, because they move in the same way that the other “wandering stars” move. Like Saturn and Jupiter, if you look at them through a telescope, they appear bigger than stars, so they were recognized to be more like planets than stars. </p>
<p>Not long after the discovery of Uranus, astronomers discovered additional wandering objects – these were named <a href="https://www.esa.int/About_Us/Welcome_to_ESA/ESA_history/Asteroids_The_discovery_of_asteroids">Ceres, Pallas, Juno and Vesta</a>. At the time they were considered planets, too. Through a telescope they look like pinpoints of light and not disks. With a small telescope, even <a href="http://www.astronomy.com/observing/sky-this-month/2018/08/neptune-at-its-best">distant Neptune appears fuzzier than a star</a>. Even though these other, new objects were called planets at first, astronomers thought they needed a different name since they appear more star-like than planet-like. </p>
<p>William Herschel (who discovered Uranus) is often said to have named them “asteroids” which means “star-like,” but <a href="https://www.skyandtelescope.com/astronomy-news/why-do-we-call-them-asteroids/">recently, Clifford Cunningham</a> claimed that the person who coined that name was Charles Burney Jr., a preeminent Greek scholar. </p>
<p>Today, just like the word “planet,” we use the word “asteroid” differently. Now it refers to objects that are rocky in composition, mostly found between Mars and Jupiter, mostly irregularly shaped, smaller than planets, but bigger than meteoroids. Most people assume there is a strict definition for what makes an object an asteroid. But there isn’t, just like there never was for the word “planet.”</p>
<p>In the 1800s the large asteroids were called planets. Students at the time likely learned that the planets were Mercury, Venus, Earth, Mars, Ceres, Vesta, Pallas, Juno, Jupiter, Saturn, Uranus and, eventually, Neptune. Most books today write that asteroids are different than planets, but there is a <a href="https://arxiv.org/abs/1805.04115">debate among astronomers</a> about whether the term “asteroid” was originally used to mean a small type of planet, rather than a different type of object altogether. </p>
<h2>How are moons different than planets?</h2>
<p>These days, scientists consider properties of these celestial objects to figure out whether an object is a planet or not. For example, you might say that shape is important; planets should be mostly spherical, while asteroids can be lumpy. As astronomers try to fix these definitions to make them more precise, we then create new problems. If we use roundness as an important distinction for objects, what should we call moons? Should moons be considered planets if they are round and asteroids if they are not round? Or are they somehow different from planets and asteroids altogether? </p>
<p>I would argue we should again look to how the word “moon” came to refer to objects that orbit planets. </p>
<p>When astronomers talk about the Moon of Earth, we capitalize the word “Moon” to indicate that it’s a proper name. That is, <a href="http://curious.astro.cornell.edu/observational-astronomy/seti-and-extraterrestrial-life/159-our-solar-system/the-sun/the-solar-system/4-what-are-the-names-of-the-earth-moon-sun-and-solar-system-beginner">the Earth’s moon has the name, Moon</a>. For much of human history, it was the only Moon known, so there was no need to have a word that referred to one celestial body orbiting another. This changed when <a href="http://galileo.rice.edu/sci/observations/jupiter_satellites.html">Galileo discovered four large objects orbiting Jupiter</a>. These are now called Io, Europa, Ganymede and Callisto, the moons of Jupiter. </p>
<p>This makes people think the technical definition of moon is a satellite of another object, and so we call lots of objects that orbit Mars, Jupiter, Saturn, Uranus, Neptune, Pluto, Eris, Makemake, Ida and a <a href="https://stardate.org/radio/program/2018-08-28">large number of other asteroids</a> moons. When you start to look at the variety of moons, some, like Ganymede and Titan, are larger than Mercury. Some are similar in size to the object they orbit. Some are small and irregularly shaped, and some have odd orbits. </p>
<p>So they are not all just like Earth’s Moon. If we try to fix the definition for what is a moon and how that differs from a planet and asteroid, we are likely going to have to reconsider the classification of some of these objects, too. You can argue that Titan has more properties in common with the planets than Pluto does, for example. You can also argue that every single particle in Saturn’s rings is an individual moon, which would mean that Saturn has billions upon billions of moons.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/300166/original/file-20191104-88419-3j0wfr.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/300166/original/file-20191104-88419-3j0wfr.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/300166/original/file-20191104-88419-3j0wfr.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/300166/original/file-20191104-88419-3j0wfr.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/300166/original/file-20191104-88419-3j0wfr.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/300166/original/file-20191104-88419-3j0wfr.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/300166/original/file-20191104-88419-3j0wfr.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/300166/original/file-20191104-88419-3j0wfr.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">Family portrait of Pluto’s moons: This composite image shows a sliver of Pluto’s large moon, Charon, and all four of Pluto’s small moons.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/image-feature/charon-and-the-small-moons-of-pluto">NASA/JHUAPL/SwRI</a></span>
</figcaption>
</figure>
<h2>Planets around other stars</h2>
<p>The most recent naming challenge astronomers face arose when they discovering planets far from our Solar System orbiting around distant stars. These objects have been called extrasolar planets, exosolar planets or <a href="http://exoplanets.org/">exoplanets</a>. </p>
<p>Astronomers are currently searching for <a href="https://arxiv.org/abs/1904.10618">exomoons</a> orbiting exoplanets. Exoplanets are being discovered that have properties unlike the planets in our Solar System, so astronomers have started putting them in categories like “hot Jupiter,” “warm Jupiter,” “super-Earth” and “mini-Neptune.” </p>
<p>Ideas for how planets form also suggest that there are planetary objects that have been flung out of orbit from their parent star. This means there are <a href="https://exoplanets.nasa.gov/resources/28/free-floating-planets-may-be-more-common-than-stars/">free-floating planets</a> not orbiting any star. Should planetary objects that are flung out of a solar system also get ejected from the elite club of planets? </p>
<p>When I teach, I end this discussion with a recommendation. Rather than arguing over planet, moon, asteroid and exoplanet, I think we need to do what Herschel and Burney did and coin a new word. For now, I use “world” in my class, but I do not offer a rigorous definition of what makes something a world and what does not. Instead, I tell my students that all of these objects are of interest to study. </p>
<h2>The Sun was once a planet</h2>
<p>A lot of people seem to feel that scientists wronged Pluto by changing its classification. I look at it that Pluto was only originally called a planet because of an accident; scientists were looking for planets beyond Neptune, and when they found Pluto they called it a planet, even though its observable properties should have led them to call it an asteroid. </p>
<p>As our understanding of this object has grown, I feel like the evidence now leads me to call Pluto something besides planet. There are other scientists who disagree, feeling Pluto still should be classified as a planet. </p>
<p>But remember: The Greeks started out calling the Sun a planet given how it moved on the sky. We now know that the properties of the Sun show it to belong in a very different category from the planets; it’s a star, not a planet. If we can stop calling the Sun a planet, why can’t we do the same to Pluto?</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/300165/original/file-20191104-88387-brm58q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/300165/original/file-20191104-88387-brm58q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/300165/original/file-20191104-88387-brm58q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/300165/original/file-20191104-88387-brm58q.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/300165/original/file-20191104-88387-brm58q.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/300165/original/file-20191104-88387-brm58q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/300165/original/file-20191104-88387-brm58q.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/300165/original/file-20191104-88387-brm58q.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">The Kepler-90 planets have a similar configuration to our solar system with small planets found orbiting close to their star, and the larger planets found farther away.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/image-feature/ames/kepler-90-system-planet-sizes">NASA/Ames Research Center/Wendy Stenzel</a></span>
</figcaption>
</figure>
<p>[ <em>Like what you’ve read? Want more?</em> <a href="https://theconversation.com/us/newsletters?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=likethis">Sign up for The Conversation’s daily newsletter</a>. ]</p><img src="https://counter.theconversation.com/content/124158/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 are still upset that Pluto was demoted from being a planet. But definitions of various celestial objects are fairly fluid. So whether it is an asteroid or moon or planet is up for debate.Christopher Palma, Associate Dean for Undergraduate Students and Teaching Professor of Astronomy & Astrophysics, Penn StateLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1188182019-06-25T12:48:29Z2019-06-25T12:48:29ZAccelerating exoplanet discovery using chemical signatures of stars<figure><img src="https://images.theconversation.com/files/280862/original/file-20190624-61729-h9lccm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Planets form from a disc of dust orbiting a star.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/birth-solar-sytem-protoplanetary-disk-155181773?studio=1">Mopic/Shutterstock.com</a></span></figcaption></figure><p>Stars are born when <a href="https://doi.org/10.1093/mnras/194.4.809">huge clouds of dust and gas collapse</a> in on themselves and ignite. These clouds are made up of raw elements, like oxygen and titanium, and <a href="http://articles.adsabs.harvard.edu/full/1987ARA%26A%2E%2E25%2E%2E%2E23S/0000071.000.html">each cloud has a unique composition</a> that imprints on the star. And within the stellar afterbirth – from the material that didn’t find its way into the star – planets are formed.</p>
<p>Finding planets orbiting distant stars, or exoplanets, is difficult. There are tried and true methods that involve using large telescopes to detect these tiny objects. But I’ve developed a faster and more powerful strategy for planet hunting that is based on the chemistry of the star. I am a <a href="http://www.nataliehinkel.com/">planetary astrophysicist</a>. Admittedly, this is a title that I made up because I wanted something that actually described what I do. I study the elements within stars, their patterns, and how they are connected to planets. </p>
<p>I created an enormous database of stars and their elemental compositions. Some of those stars have planets orbiting them; others don’t. When a star has an orbiting planet, it could be the smaller rocky type, a large gas one, or both. However, not every star can have a giant Jupiter-sized planets – since these planets require a huge amount of elements and materials to form. </p>
<p>Together with a small team of researchers from Arizona State University, University of California, Riverside, Vanderbilt University and New York University, I used software that searches for complex patterns within stellar data to figure out <a href="https://arxiv.org/abs/1805.12144">which stars are likely to have planets orbiting</a> them based only on the star’s chemical composition. </p>
<p>Now, instead of looking through huge all-sky telescope surveys hoping to find a signature of a planet, my team can fast-track the discovery and characterization of planets by analyzing the composition of their host stars. Of the 4,200 stars that we analyzed, we found that approximately 360 stars have a greater than 90% chance of hosting a giant planet. Now we are working to get time on a telescope to test our predictions. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/281011/original/file-20190624-97785-1tt50j2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/281011/original/file-20190624-97785-1tt50j2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/281011/original/file-20190624-97785-1tt50j2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281011/original/file-20190624-97785-1tt50j2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281011/original/file-20190624-97785-1tt50j2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281011/original/file-20190624-97785-1tt50j2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281011/original/file-20190624-97785-1tt50j2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281011/original/file-20190624-97785-1tt50j2.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">Stars and planets are chemically linked to one another, since they both form within the same molecular cloud. The raw ingredients within the planet ultimately creates an environment that’s ‘alive’ and conducive to life – or not.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/image-feature/light-echoes-used-to-study-protoplanetary-disks">NASA/JPL-Caltech</a></span>
</figcaption>
</figure>
<h2>The Hypatia Catalog and its elements</h2>
<p>The algorithm we developed uses the chemical composition of stars that we know have orbiting giant planets to determine which combination of elements – or chemical fingerprint – is common to stars that host planets. My team then used this algorithm to look at the chemistry of stars not known to have planets to provide a prediction score that a star is likely to host a planet.</p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/281039/original/file-20190624-97762-1eu1vvw.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/281039/original/file-20190624-97762-1eu1vvw.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281039/original/file-20190624-97762-1eu1vvw.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281039/original/file-20190624-97762-1eu1vvw.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281039/original/file-20190624-97762-1eu1vvw.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281039/original/file-20190624-97762-1eu1vvw.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281039/original/file-20190624-97762-1eu1vvw.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281039/original/file-20190624-97762-1eu1vvw.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"></a>
<figcaption>
<span class="caption">This is the logo for the Hypatia Catalog showing an artist depiction of Hypatia. Some of the most important elements in stars are listed along the outside.</span>
<span class="attribution"><span class="source">Nahks Tr'Ehnl</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Light shines from the interior of a star and is absorbed by atoms in its upper layer, creating a stellar spectra. The absorbed wavelengths reveal what type of elements from the periodic table are present. Using a technique called <a href="https://imagine.gsfc.nasa.gov/science/toolbox/spectra1.html">spectroscopy</a>, scientists are able to measure the light from the star and measure the amount, or abundance, of those elements. I compiled the largest catalog of elements in nearby stars in the <a href="https://www.hypatiacatalog.com/">Hypatia Catalog</a>. I named it to honor one of the first known female astronomers who was a powerhouse in 400 A.D. </p>
<p>I use the Hypatia Catalog to understand planets from a more chemical or compositional perspective. Each star is made up of different combinations and quantities of elements, which is reflected in the planets orbiting the star. There can be a huge variety in the chemical composition of planets from their interiors to their surfaces. </p>
<h2>Physically detecting exoplanets</h2>
<p>There are two primary techniques for finding or detecting exoplanets.</p>
<p>The first is the “radial velocity” technique, which detects when a star wobbles in the presence of a planet with a strong gravitational force. </p>
<p>Another strategy is to look for a “blip” in the light a star emits, which happens when a planet moves in front of the star (with respect to the Earth) and actually dims the stellar light. Both of these methods look for ways that the planet influences the star. However, it’s difficult to detect planets because they are so small compared with their star – it would be like trying to observe a person being influenced by a raindrop.</p>
<p>The radial velocity and “blip” methods look at the physical relationship between a star and a planet. These are important because they determine the temperature, orbit and dynamics that exoplanet scientists use to define whether a planet may be habitable. However, none of these detection methods take into account what the star and planet are made of. And yet, understanding the composition of the planet is vital to predicting whether it is habitable. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/280812/original/file-20190621-61775-ynllx.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/280812/original/file-20190621-61775-ynllx.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=386&fit=crop&dpr=1 600w, https://images.theconversation.com/files/280812/original/file-20190621-61775-ynllx.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=386&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/280812/original/file-20190621-61775-ynllx.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=386&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/280812/original/file-20190621-61775-ynllx.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=485&fit=crop&dpr=1 754w, https://images.theconversation.com/files/280812/original/file-20190621-61775-ynllx.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=485&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/280812/original/file-20190621-61775-ynllx.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=485&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">An artist’s impression of how common planets are around the stars in the Milky Way. The planets, their orbits and their host stars are all vastly magnified.</span>
<span class="attribution"><a class="source" href="https://www.eso.org/public/norway/images/eso1204a/?lang">ESO/M. Kornmesser</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>Planetary composition is key to habitability</h2>
<p>The planet Earth is “alive” – it moves and shifts in a complex way. The surface conditions, like temperature and weather, are maintained by relying on the movement of the continents, for example by <a href="https://en.wikipedia.org/wiki/Plate_tectonics">plate tectonics</a>. The cycling of different elements or molecules, like the <a href="https://en.wikipedia.org/wiki/Oxygen_cycle">oxygen-carbon dioxide cycle</a>, helps organisms breathe. In order for exoplanets to truly be habitable for life, basic elements must be present within the planet to make sure that these key processes happen. </p>
<p>We exoplanetary scientists don’t currently have the technology to directly observe the surface or interior of a planet outside of our Solar System. This is partially because planets are so small compared to their star, so we’d need high-powered telescopes. It is also because planets don’t shine or emit their own light. </p>
<p>Therefore, my colleagues and I use the stellar composition as a proxy for the planet’s makeup. The <a href="https://arxiv.org/abs/1805.12144">algorithm that we developed</a> is a unique one, because it looks at the elemental link between a star and its planet from the very beginning. This makes the approximately 360 likely giant planet host stars we found even more remarkable, because they were identified by the chemical fingerprint. </p>
<p>As part of <a href="https://arxiv.org/abs/1805.12144">this research published</a> in The Astrophysical Journal, we studied a variety of different elements, up to 16 at a time. We wanted to see how those elements influenced each other and which were the most important for planet detection and possible formation. </p>
<p>We found that carbon, oxygen, sodium and iron were the most important elements when predicting that a star had a giant planet. Carbon, oxygen and iron are all very important elements when it comes to building rocky and or gas planets. However, we were surprised to discover that sodium also seemed to be a critical ingredient of stars that form giant planets. Sodium is not considered to be a major planet-forming element within the Solar System.</p>
<p>For practical reasons we didn’t use the algorithm to look at Earth-like planets. Rather we focused our study, and trained our algorithm, on big gaseous planets where humans couldn’t survive. Most of the exoplanets that astronomers have discovered to date have sizes similar to Neptune or Jupiter because they are easier to detect. </p>
<p>However, as new missions like <a href="https://tess.mit.edu/">TESS</a> and <a href="http://sci.esa.int/cheops/">CHEOPS</a> discover smaller, Earth-sized planets, we will have more data with which to train the algorithm to look for rocky planets like Earth. </p>
<p>[ <em><a href="https://theconversation.com/us/newsletters?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=thanksforreading">Thanks for reading! We can send you The Conversation’s stories every day in an informative email. Sign up today.</a></em> ]</p><img src="https://counter.theconversation.com/content/118818/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Natalie Hinkel receives funding from the Vanderbilt Office of the Provost through the Vanderbilt Initiative in Data-intensive Astrophysics (VIDA) fellowship and by NASA’s Nexus for Solar System Science (NExSS) research coordination network at Arizona State University.</span></em></p>It is always exciting to discover new planets beyond our Solar System. Now a planetary astrophysicist is using a star’s chemistry to predict which ones are likely to host giant planets.Natalie Hinkel, Planetary Astrophysicist, Senior Research Scientist at the Southwest Research Institute and Co-Investigator for the Nexus for Exoplanet System Science (NExSS), Arizona State UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1051272018-10-31T01:40:49Z2018-10-31T01:40:49ZCurious Kids: If a star explodes, will it destroy Earth?<figure><img src="https://images.theconversation.com/files/243122/original/file-20181030-76396-yep6vj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The good thing about space is that – even though it has lots of dangerous stuff floating in it, and lots of exploding stars – it's so big and empty that it almost doesn't matter</span> <span class="attribution"><a class="source" href="https://www.nasa.gov/mission_pages/chandra/exploded-star-blooms-like-flower-photo.html">NASA/CXC/U.Texas</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p><em>This is an article from <a href="https://theconversation.com/au/topics/curious-kids-36782">Curious Kids</a>, a series for children. The Conversation is asking kids to send in questions they’d like an expert to answer. All questions are welcome: find out how to enter at the bottom. You might also like the podcast <a href="http://www.abc.net.au/kidslisten/imagine-this/">Imagine This</a>, a co-production between ABC KIDS listen and The Conversation, based on Curious Kids.</em> </p>
<hr>
<blockquote>
<p><strong>If a star explodes, will it destroy the Earth? – Sascha, age 8, Hurstbridge Victoria.</strong></p>
</blockquote>
<p>What a great question. Thank you, Sascha. The answer is a resounding “I hope not!”</p>
<p>Luckily for us, not all stars explode and then die. When stars age, they change from a dwarf star (our Sun is actually currently a dwarf star) into a giant star. If a star is big enough it can then explode in what we call a “core-collapse supernova”. But it would need to be around ten times more massive than our Sun for that to happen.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/241570/original/file-20181022-105757-1t5jocp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/241570/original/file-20181022-105757-1t5jocp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/241570/original/file-20181022-105757-1t5jocp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/241570/original/file-20181022-105757-1t5jocp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/241570/original/file-20181022-105757-1t5jocp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/241570/original/file-20181022-105757-1t5jocp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/241570/original/file-20181022-105757-1t5jocp.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">
<figcaption>
<span class="caption">Crab Nebula - the remnant of an exploding star.</span>
<span class="attribution"><span class="source">Wikipedia</span></span>
</figcaption>
</figure>
<p>So, we’re safe from the Sun exploding. But that doesn’t mean we’re safe in general, because giant stars are big! </p>
<p>In several billion years, the Sun will run out of hydrogen (that’s a gas it burns for fuel) and as it shifts to sticking different atoms together it will expand outwards. First, it will swallow Mercury. Then Venus. And then it will swallow Earth.</p>
<p>This is not great for Earth.</p>
<p>The good news is we have billions of years to prepare for this and leave the planet, if humans are even still around by then.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/Tth9G90IkWY?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">This animation shows the supernova event which created the Crab Nebula. Credit: ESA/Hubble (M. Kornmesser & L. L. Christensen)</span></figcaption>
</figure>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/curious-kids-why-do-stars-twinkle-81188">Curious Kids: Why do stars twinkle?</a>
</strong>
</em>
</p>
<hr>
<p>But you asked about exploding stars. So are there stars <em>other than the Sun</em>, which might explode soon close to us?</p>
<p>Yes, there are! As long as by “soon” we mean within a million years. </p>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/241571/original/file-20181022-105748-15yxqvw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/241571/original/file-20181022-105748-15yxqvw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=925&fit=crop&dpr=1 600w, https://images.theconversation.com/files/241571/original/file-20181022-105748-15yxqvw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=925&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/241571/original/file-20181022-105748-15yxqvw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=925&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/241571/original/file-20181022-105748-15yxqvw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1162&fit=crop&dpr=1 754w, https://images.theconversation.com/files/241571/original/file-20181022-105748-15yxqvw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1162&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/241571/original/file-20181022-105748-15yxqvw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1162&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The Orion nebula and Betelgeuse.</span>
<span class="attribution"><span class="source">Wikipedia</span></span>
</figcaption>
</figure>
<p>If you find the constellation Orion in the sky, there is a bright red star at one end – this is Betelgeuse. It is a red supergiant star – so big that if we swapped its position with the Sun, Betelgeuse would swallow Mars, and the asteroid belt. It might also swallow Jupiter as well. </p>
<p>And within the next million years Betelgeuse is expected to explode. Luckily for us, it is around 600 light years away, far enough that when it explodes Earth is safe. </p>
<p>When Betelgeuse explodes it will be so bright that it will outshine the full moon for over a month. We’ll be able to see it in the day time and walk around at night, able to see solely from Betelgeuse’s light.</p>
<p>But it won’t destroy the Earth. </p>
<p>The good thing about space is that – even though it has lots of dangerous stuff floating in it – it’s so big and empty that it almost doesn’t matter. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/241572/original/file-20181022-105770-oqy3ov.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/241572/original/file-20181022-105770-oqy3ov.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/241572/original/file-20181022-105770-oqy3ov.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/241572/original/file-20181022-105770-oqy3ov.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/241572/original/file-20181022-105770-oqy3ov.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/241572/original/file-20181022-105770-oqy3ov.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/241572/original/file-20181022-105770-oqy3ov.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The Andromeda galaxy - currently heading straight towards us!</span>
<span class="attribution"><span class="source">Wikipedia</span></span>
</figcaption>
</figure>
<p>Two galaxies smashing together and merging into one sounds catastrophic. But space is so empty that even with the hundreds of billions of stars from the Andromeda galaxy shooting towards us, we don’t expect any collisions between stars at all. There’s just too much space between them. That’s not just with our Sun, but with <em>any</em> of the billions of stars in the Milky Way. </p>
<p>It’s crazy how big space is!</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/curious-kids-why-is-the-earth-round-80311">Curious Kids: Why is the Earth round?</a>
</strong>
</em>
</p>
<hr>
<p><em>Hello, curious kids! Have you got a question you’d like an expert to answer? Ask an adult to send your question to us. You can:</em></p>
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<figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=376&fit=crop&dpr=1 600w, https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=376&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=376&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=472&fit=crop&dpr=1 754w, https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=472&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=472&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
<span class="attribution"><a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p><em>Please tell us your name, age and which city you live in. You can send an audio recording of your question too, if you want. Send as many questions as you like! We won’t be able to answer every question but we will do our best.</em></p><img src="https://counter.theconversation.com/content/105127/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Samuel Hinton 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>Are there stars other than the Sun that might explode soon close to us? Yes, there are! As long as by ‘soon’ we mean within a million years.Samuel Hinton, PhD, The University of QueenslandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1019772018-08-28T20:19:51Z2018-08-28T20:19:51ZCurious Kids: Where are all the other galaxies hidden?<figure><img src="https://images.theconversation.com/files/233003/original/file-20180822-149484-cs44to.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The other galaxies are there, but they are hiding a very long way away.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/galaxy-nebula-elements-this-image-furnished-530443579">www.shutterstock.com</a></span></figcaption></figure><p><em>This is an article from <a href="https://theconversation.com/au/topics/curious-kids-36782">Curious Kids</a>, a series for children. The Conversation is asking kids to send in questions they’d like an expert to answer. All questions are welcome – serious, weird or wacky! You might also like the podcast <a href="http://www.abc.net.au/kidslisten/imagine-this/">Imagine This</a>, a co-production between ABC KIDS listen and The Conversation, based on Curious Kids.</em> </p>
<hr>
<blockquote>
<p><strong>Where are all the other galaxies hidden? – Sasha, age 7, Sydney.</strong></p>
</blockquote>
<hr>
<p>Hi Sasha, </p>
<p>Thanks for sending in your question.</p>
<p>Almost everything in our universe is high above the clouds, even higher than an aeroplane. If you keep going up, up, up… you get to outer space. There is a lot of empty space up there, as well as some fascinating things like planets, stars and beautiful clouds of gas.</p>
<p>Imagine that you could launch yourself on a very fast spaceship — travelling as fast as lightning — the first place you would reach would be the planets in our solar system: Mercury, Venus, Mars, Jupiter, Saturn, Uranus and Neptune. At that speed, you could travel to the planets in a few minutes. Which would you visit first?</p>
<p>If you went even further, travelling for almost five years on your spaceship you would reach the nearest stars. Many of these stars live in twos or threes, and have their very own planets too. We don’t know whether there are any animals, plants, birds or fish on these planets, or perhaps creatures that we don’t have here on Earth. Maybe that’s a mission for astronaut Sasha. Can you imagine what life on other planets might be like?</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/curious-kids-will-the-universe-expand-forever-or-contract-in-a-big-crunch-96209">Curious Kids: will the universe expand forever, or contract in a big crunch?</a>
</strong>
</em>
</p>
<hr>
<p>If you zoom even further on your spaceship, travelling for thousands of years, you will start to see that we live in a huge spiral galaxy containing two hundred billion stars. It’s called the Milky Way and you can see it glowing in the night sky as a band of light. Have you ever seen the Milky Way?</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/233007/original/file-20180822-149481-1uvtm1h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/233007/original/file-20180822-149481-1uvtm1h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/233007/original/file-20180822-149481-1uvtm1h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=342&fit=crop&dpr=1 600w, https://images.theconversation.com/files/233007/original/file-20180822-149481-1uvtm1h.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=342&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/233007/original/file-20180822-149481-1uvtm1h.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=342&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/233007/original/file-20180822-149481-1uvtm1h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=430&fit=crop&dpr=1 754w, https://images.theconversation.com/files/233007/original/file-20180822-149481-1uvtm1h.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=430&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/233007/original/file-20180822-149481-1uvtm1h.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=430&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 artist’s impression of the Milky Way galaxy, which is where you find our solar system.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<p>Now, keep travelling out of our Milky Way, for more than two million years (you’ll be very old by then). You will finally reach the nearest spiral galaxy, called the Andromeda galaxy. It’s hard to believe, but all the other galaxies are even further away than this. Some galaxies are so far away they would take thousands of millions of years to reach.</p>
<p>So to answer your question Sasha, the other galaxies are there, but they are hiding a very long way away. That’s why we can’t easily see them when we look up at the night sky. Luckily, we don’t have to fly in a spaceship for millions of years to find other galaxies. Scientists like me, astronomers who study space, can use huge telescopes to study the light coming from galaxies and see what they are up to.</p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/curious-kids-whats-going-to-happen-to-the-sun-in-the-future-will-it-explode-78029">Curious Kids: What's going to happen to the Sun in the future? Will it explode?</a>
</strong>
</em>
</p>
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<p>Galaxies are fascinating. Like people, some are young and others are old. Some galaxies are made up of hot stars that have only recently been born, like baby stars. Other galaxies are colder and contain mostly older stars. Galaxies can be active too. As gravity pulls them towards one another, they can merge together and collide. This will eventually happen to the Milky Way, which will collide with the Andromeda galaxy in about four billion years’ time. When that happens, the Sun will keep shining but our night sky will look very different.</p>
<p>I hope you will keep looking up at the stars, astronaut Sasha. It’s a fascinating place out there. Let me know if you find life on those planets!</p>
<hr>
<p><em>Hello, curious kids! Have you got a question you’d like an expert to answer? Ask an adult to send your question to us. They can:</em></p>
<p><em>* Email your question to curiouskids@theconversation.edu.au
<br>
* Tell us on <a href="https://twitter.com/ConversationEDU">Twitter</a></em></p>
<figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=376&fit=crop&dpr=1 600w, https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=376&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=376&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=472&fit=crop&dpr=1 754w, https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=472&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=472&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
<span class="attribution"><a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p><em>Please tell us your name, age and which city you live in. You can send an audio recording of your question too, if you want. Send as many questions as you like! We won’t be able to answer every question but we will do our best.</em></p><img src="https://counter.theconversation.com/content/101977/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Lisa Harvey-Smith has authored a book called 'When Galaxies Collide' (Melbourne University Publishing, 2018). </span></em></p>We are in the Milky Way. If you travelled on an extremely fast spaceship for more than two million years, you would reach our neighbour, the Andromeda galaxy. All other galaxies are even further away.Lisa Harvey-Smith, Astronomer, CSIROLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/811882017-09-03T20:01:57Z2017-09-03T20:01:57ZCurious Kids: Why do stars twinkle?<figure><img src="https://images.theconversation.com/files/180452/original/file-20170801-22169-m3uof.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C4000%2C2663&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Lasers being shone from the European Southern Observatory's Very Large Telescope in Chile.
These lasers help remove the twinkles in the night sky and help astronomers see stars clearer on Earth than ever before.</span> <span class="attribution"><a class="source" href="http://eso.org/public/images/16fkc16776-cc/">F. Kamphues/ESO</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p><em>This is an article from <a href="https://theconversation.com/au/topics/curious-kids-36782">Curious Kids</a>, a series for children. The Conversation is asking kids to send in questions they’d like an expert to answer. All questions are welcome – serious, weird or wacky!</em> </p>
<blockquote>
<p><strong>Why do stars twinkle? – Max, 3, Earlwood.</strong> </p>
</blockquote>
<p>Max, that’s a fantastic question! And the answer, it turns out, is all around us.</p>
<p>Have you ever been out on a really hot day? Like ice-cream-melting-through-your-hands hot? Well, if you have, you may have noticed trees near the horizon being a bit wobbly or blurry. It looks strange, and something very similar is happening when we see stars twinkle in the night sky. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/179730/original/file-20170726-30125-ezpont.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/179730/original/file-20170726-30125-ezpont.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/179730/original/file-20170726-30125-ezpont.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/179730/original/file-20170726-30125-ezpont.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/179730/original/file-20170726-30125-ezpont.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/179730/original/file-20170726-30125-ezpont.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/179730/original/file-20170726-30125-ezpont.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/179730/original/file-20170726-30125-ezpont.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">The light from the setting Sun bends through the atmosphere creating a mirage. This mirage behaves the same way as a star’s twinkling light.</span>
<span class="attribution"><span class="source">Brocken Inaglory</span></span>
</figcaption>
</figure>
<p>When we look up, we don’t just look into space. We’re actually looking at space through all of the air above us, called <a href="https://theconversation.com/curious-kids-why-is-the-sky-blue-and-where-does-it-start-81165">the atmosphere</a>. </p>
<p>The Earth’s atmosphere is a layer of air. A whopping 120 kilometres tall, or more. This air, around and above us, moves and swirls around the Earth at different speeds. </p>
<p>How fast this air travels, depends on its temperature. When the air is hot, it has loads of energy and loves to move around. But when the air is cold, it doesn’t move as much.</p>
<p>Hot air is also lighter than cold air, so it rises past, and mixes with, the cold air around it. This mixing creates swirls in the atmosphere known as “turbulence”.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/179619/original/file-20170725-28293-19z3sh4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/179619/original/file-20170725-28293-19z3sh4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/179619/original/file-20170725-28293-19z3sh4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=479&fit=crop&dpr=1 600w, https://images.theconversation.com/files/179619/original/file-20170725-28293-19z3sh4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=479&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/179619/original/file-20170725-28293-19z3sh4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=479&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/179619/original/file-20170725-28293-19z3sh4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=602&fit=crop&dpr=1 754w, https://images.theconversation.com/files/179619/original/file-20170725-28293-19z3sh4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=602&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/179619/original/file-20170725-28293-19z3sh4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=602&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">van Gogh’s painting ‘The Starry Night’ artistically shows the stars light being swirled by turbulence in our atmosphere.</span>
<span class="attribution"><span class="source">Vincent van Gogh, Wikimedia</span></span>
</figcaption>
</figure>
<p>Air can also be bumped around as it passes up and down hills and mountains on the Earth’s surface, creating waves that reach into the upper atmosphere. These waves disturb the air above, also causing turbulence.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/180456/original/file-20170801-5515-f2dvba.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/180456/original/file-20170801-5515-f2dvba.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/180456/original/file-20170801-5515-f2dvba.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/180456/original/file-20170801-5515-f2dvba.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/180456/original/file-20170801-5515-f2dvba.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/180456/original/file-20170801-5515-f2dvba.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/180456/original/file-20170801-5515-f2dvba.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/180456/original/file-20170801-5515-f2dvba.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">Air can be pushed up as it passes above mountains and hills, creating waves in the atmosphere. These waves can create really cool cloud patterns like this near the Moul n'ga Cirque in Southeast Algeria.</span>
<span class="attribution"><span class="source">Pir6mon/wikimedia</span></span>
</figcaption>
</figure>
<p>As light from a star races through our atmosphere, it bounces and bumps through the different layers, bending the light before you see it. Since the hot and cold layers of air keep moving, the bending of the light changes too, which causes the star’s appearance to wobble or twinkle.</p>
<p>Indigenous Australians and Torres Strait Islanders have been observing the twinkling of stars for thousands of years. The stars’ twinkling shows how the winds are moving, which can really help when <a href="https://theconversation.com/stories-from-the-sky-astronomy-in-indigenous-knowledge-33140">predicting weather</a> - like really hot days.</p>
<h2>Correcting the twinkle</h2>
<p>While twinkling looks pretty, astronomers find it very annoying. This is because it blurs the things we want to see, like distant galaxies.</p>
<p>What can we do about this?</p>
<p>Well, space is the best place to see a star without a twinkle. However, getting big telescopes into space is very hard. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/178607/original/file-20170718-21994-1k9x6ub.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/178607/original/file-20170718-21994-1k9x6ub.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=433&fit=crop&dpr=1 600w, https://images.theconversation.com/files/178607/original/file-20170718-21994-1k9x6ub.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=433&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/178607/original/file-20170718-21994-1k9x6ub.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=433&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/178607/original/file-20170718-21994-1k9x6ub.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=544&fit=crop&dpr=1 754w, https://images.theconversation.com/files/178607/original/file-20170718-21994-1k9x6ub.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=544&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/178607/original/file-20170718-21994-1k9x6ub.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=544&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">NASA’s Spitzer Space Telescope snapped this photo of hundreds of thousands of stars lurking in the Milky Way Galaxy, thanks to its infrared photography equipment.</span>
<span class="attribution"><a class="source" href="https://images.nasa.gov/#/details-PIA03654.html">NASA/JPL-Caltech</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>We can build big telescopes on the ground that use <a href="https://www.youtube.com/watch?v=gDGvNyVApgg">lasers and bendable mirrors</a> - bending the mirrors to match the twinkling starlight. This then shows us the whole universe, as if the atmosphere vanished above us!</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/179567/original/file-20170725-11526-1676g6e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/179567/original/file-20170725-11526-1676g6e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/179567/original/file-20170725-11526-1676g6e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/179567/original/file-20170725-11526-1676g6e.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/179567/original/file-20170725-11526-1676g6e.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/179567/original/file-20170725-11526-1676g6e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/179567/original/file-20170725-11526-1676g6e.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/179567/original/file-20170725-11526-1676g6e.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"></a>
<figcaption>
<span class="caption">Astronomers use lasers to work out how the atmosphere moves, so that they can remove the twinkle from stars they observe. This whole process is called ‘adaptive optics’.</span>
<span class="attribution"><span class="source">G. Hüdepohl/ESO</span></span>
</figcaption>
</figure>
<h2>But what about the planets?</h2>
<p>So that’s the story of why stars appear to twinkle in the sky. If you look really carefully, you might have noticed that planets, like Venus and Jupiter, don’t seem to twinkle like the stars around them.</p>
<p>Why is that? </p>
<p>Well, if you look at a star through even the biggest telescope, you still just see a tiny point of light. This light comes through the atmosphere in a tiny beam - that can be easily knocked around.</p>
<p>If you look at the planets through a telescope, you see their disks - they are close enough to us that we can “zoom in”, and see a planet, rather than a point of light. That means that the light from those planets comes through the atmosphere in a much thicker beam than that from a star - and that thicker beam is much harder to knock around. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/179624/original/file-20170725-28293-11x063q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/179624/original/file-20170725-28293-11x063q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/179624/original/file-20170725-28293-11x063q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=375&fit=crop&dpr=1 600w, https://images.theconversation.com/files/179624/original/file-20170725-28293-11x063q.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=375&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/179624/original/file-20170725-28293-11x063q.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=375&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/179624/original/file-20170725-28293-11x063q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=471&fit=crop&dpr=1 754w, https://images.theconversation.com/files/179624/original/file-20170725-28293-11x063q.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=471&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/179624/original/file-20170725-28293-11x063q.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=471&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Only stars twinkle in the night sky. Planets in our solar system are too close and big for them to twinkle. Venus is the brightest light nearer to the centre. Jupiter is just north-west of Venus.</span>
<span class="attribution"><span class="source">Brocken Inaglory/Wikimedia</span></span>
</figcaption>
</figure>
<p>As a result, the planets barely flicker, while the stars twinkle like crazy.</p>
<hr>
<p><em>Hello, curious kids! Have you got a question you’d like an expert to answer? Ask an adult to send your question to us. They can:</em></p>
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<figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=376&fit=crop&dpr=1 600w, https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=376&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=376&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=472&fit=crop&dpr=1 754w, https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=472&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=472&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="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
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<p><em>Please tell us your name, age, and which city you live in. You can send an audio recording of your question too, if you want. Send as many questions as you like! We won’t be able to answer every question but we will do our best.</em></p><img src="https://counter.theconversation.com/content/81188/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jake Clark is supported by an Australian Government Research Training Program (RTP) Scholarship.</span></em></p><p class="fine-print"><em><span>Belinda Nicholson is supported by an Australian Government Research Training Program (RTP) Scholarship.
</span></em></p><p class="fine-print"><em><span>Brad Carter and Jonti Horner do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>How exactly do the stars twinkle in the night sky? As it turns out, the answer is full of hot air… and cold air.Jake Clark, PhD Student, University of Southern QueenslandBelinda Nicholson, PhD Candidate, University of Southern QueenslandBrad Carter, Professor (Physics), University of Southern QueenslandJonti Horner, Vice Chancellor's Senior Research Fellow, University of Southern QueenslandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/648872016-11-27T19:14:29Z2016-11-27T19:14:29ZA Galah to help capture millions of rainbows to map the history of the Milky Way<figure><img src="https://images.theconversation.com/files/140875/original/image-20161007-21447-t8o7h5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Untangling the history of the Milky Way.</span> <span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:ESO_-_Milky_Way.jpg">ESO/S Brunier</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>Our galaxy, the Milky Way, contains at least 100 billion stars. Over the centuries, astronomers have scoured the skies, developing a <a href="https://map.gsfc.nasa.gov/universe/rel_stars.html">thorough understanding of the lives of those stars</a>, from their <a href="http://earthsky.org/space/orion-nebula-jewel-in-orions-sword">formation in vast nebulae</a> to their <a href="http://www.abc.net.au/news/2016-01-15/newly-discovered-supernova-most-powerful-explosion-ever-seen/7086138">fiery and spectacular deaths</a>.</p>
<p>But how has our galaxy changed over time? Where did the stars we see today form, and which of them are siblings, formed together from the same cloud of material? </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/140878/original/image-20161007-21414-u2lye7.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/140878/original/image-20161007-21414-u2lye7.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/140878/original/image-20161007-21414-u2lye7.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/140878/original/image-20161007-21414-u2lye7.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/140878/original/image-20161007-21414-u2lye7.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/140878/original/image-20161007-21414-u2lye7.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/140878/original/image-20161007-21414-u2lye7.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/140878/original/image-20161007-21414-u2lye7.png?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"></a>
<figcaption>
<span class="caption">The lives of stars.</span>
<span class="attribution"><span class="source">Wikimedia/cmglee/NASA Goddard Space Flight Center</span></span>
</figcaption>
</figure>
<p>To answer these questions we need to perform <a href="https://www.aao.gov.au/public/galactic-archaeology">Galactic archaeology</a>. To do this, an ambitious Australian-led observing survey, called <a href="https://galah-survey.org/">Galah</a>, is undertaking the immense task of capturing millions of rainbows to disentangle our galaxy’s story.</p>
<h2>Birds of a feather</h2>
<p>When we break the light from a star into its component colours, the spectrum is laced with dark lines. These are the telltale fingerprints of the various atomic and molecular species present in the star’s outer layers.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/140882/original/image-20161007-21443-1vfyqxl.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/140882/original/image-20161007-21443-1vfyqxl.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/140882/original/image-20161007-21443-1vfyqxl.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=176&fit=crop&dpr=1 600w, https://images.theconversation.com/files/140882/original/image-20161007-21443-1vfyqxl.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=176&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/140882/original/image-20161007-21443-1vfyqxl.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=176&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/140882/original/image-20161007-21443-1vfyqxl.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=221&fit=crop&dpr=1 754w, https://images.theconversation.com/files/140882/original/image-20161007-21443-1vfyqxl.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=221&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/140882/original/image-20161007-21443-1vfyqxl.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=221&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 Fraunhofer lines - absorption lines in the sun’s spectrum that signpost the chemical composition of its outer atmosphere.</span>
<span class="attribution"><span class="source">Wikimedia/nl:Gebruiker:MaureenV/Phrood/Saperaud</span></span>
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</figure>
<p>By studying those lines we can <a href="http://spiff.rit.edu/classes/phys230/lectures/spec_interp/spec_interp.html">learn a great deal about the star</a>, such as how fast it spins, its temperature, and what elements it is made of. We can even use them to <a href="https://theconversation.com/what-the-weather-is-like-on-a-star-can-help-in-the-search-for-life-56275">study stellar magnetic fields</a>.</p>
<p>In essence, stars turn hydrogen and helium into heavier elements. When they die, they return that material to the galaxy, to be incorporated in the next generation of stars. </p>
<p>Most stars form in <a href="http://www.atnf.csiro.au/outreach/education/senior/astrophysics/stellarevolution_clusters.html">clusters</a>, groups of hundreds to millions of stars that <a href="http://www.atnf.csiro.au/outreach/education/senior/astrophysics/stellarevolution_formation.html">form at the same time in a vast nebula</a>. Each nebula will have a unique composition, seeded by the death throes of the previous generation of stars in the distant past. </p>
<p>We also know that different types of stars return different elements to the galaxy at the end of their lifetimes. Because of this, astronomers can use the elemental patterns in present-day stars to explore what kinds of stars were in our galaxy in the past.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/144313/original/image-20161103-27215-ankcnl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/144313/original/image-20161103-27215-ankcnl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/144313/original/image-20161103-27215-ankcnl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/144313/original/image-20161103-27215-ankcnl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/144313/original/image-20161103-27215-ankcnl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/144313/original/image-20161103-27215-ankcnl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/144313/original/image-20161103-27215-ankcnl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/144313/original/image-20161103-27215-ankcnl.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">When a star like the Sun comes to the end of its life, it blows off its outer layers to form a planetary nebula – ejecting gas that will form the next generation of stars. The Helix nebula (pictured) is one of the finest examples in the night sky.</span>
<span class="attribution"><span class="source">NASA, ESA, and C R O'Dell (Vanderbilt University)</span></span>
</figcaption>
</figure>
<p>On timescales of millions of years, stars escape from the clusters in which they formed and migrate around the disk of the galaxy.</p>
<p>If we can use spectra to measure the compositions of many stars, we should be able to identify those that are made of the same stuff. The common origins of widely scattered stars is thus revealed by their matching compositions.</p>
<p>That brings us to <a href="http://galah-survey.org">Galah</a>.</p>
<h2>Hatching the idea for Galah</h2>
<p>Galactic archaeology with <a href="https://www.aao.gov.au/science/instruments/current/HERMES">HERMES</a> (<a href="http://galah-survey.org">Galah</a>) is a massive observational project using the <a href="https://www.aao.gov.au/about-us/anglo-australian-telescope">3.9-metre Anglo-Australian Telescope</a> at <a href="http://www.sidingspringobservatory.com.au/">Siding Spring Observatory</a>. Since its start, in late 2013, the survey has collected more than 250,000 spectra, and that number grows every month. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/3ZV7c9xBFuM?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Each red and blue point shows an individual GALAH target, with the blue as dwarfs and red as giants.</span></figcaption>
</figure>
<p>To make such a large project possible, Galah uses robots to position fibre optic cables to catch starlight. These allow the <a href="https://galah-survey.org/members">Galah team</a> to observe around 350 stars simultaneously in a region of sky four times the diameter of the full Moon.</p>
<p>After about an hour staring at one group of stars, Galah moves on, scanning field after field to build its catalogue of stellar spectra. When the project is complete, more than a million rainbows will be caught, each <a href="https://galah-survey.org/survey_design">in exquisite detail</a>.</p>
<h2>In good company</h2>
<p>The past few years have seen a worldwide boom in galactic archaeology. Several survey projects are going on around the globe, each filling a unique niche, and even larger projects are planned for the future. </p>
<p>While each of these surveys has a particular goal, when brought together they form a scientific superset that is greater than the sum of its parts. </p>
<p>The <a href="https://www.sdss3.org/surveys/apogee.php">APOGEE survey</a> studies red giant stars throughout the Milky Way using the 3.5-metre Sloan telescope in the United States. </p>
<p>Because it observes at infrared wavelengths, it is the only large survey that can peer through the dust that pervades our galaxy. This allows APOGEE to collect data on stars across the entire galaxy.</p>
<p>The disk of our galaxy, which contains the great majority of stars, is surrounded by a roughly spherical halo which consists of ancient stars. The halo hosts the mysterious globular clusters – spherical swarms of millions of tightly packed stars. </p>
<p>The <a href="https://www.gaia-eso.eu/">Gaia-ESO Survey</a> targets <a href="https://dept.astro.lsa.umich.edu/ugactivities/Labs/MWgalStruct/index.html">all these populations and more</a>, using two different visible-light instruments at the 8-metre Very Large Telescope in Chile.</p>
<p><a href="https://galah-survey.org/">Galah</a>, by contrast, focuses mainly our galaxy’s disk, where the great bulk of its stars reside. By obtaining such a huge sample of stellar spectra, Galah is the perfect complement to these two more focused surveys, providing the context in which their results can be understood. </p>
<h2>Flying to the future with Gaia</h2>
<p>While Galah and its fellow archaeological surveys have been farming the night sky, the <a href="https://theconversation.com/how-were-helping-the-gaia-mission-map-a-billion-stars-to-unparalleled-precision-65602">Gaia</a> spacecraft has been busy pulling together a different, but complementary, data set. </p>
<p>Launched in 2013 on an initial five-year mission, Gaia is continually scouring the sky, repeatedly observing more than a billion stars, measuring their positions with unprecedented precision. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/144316/original/image-20161103-27234-146ojxx.gif?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/144316/original/image-20161103-27234-146ojxx.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/144316/original/image-20161103-27234-146ojxx.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=532&fit=crop&dpr=1 600w, https://images.theconversation.com/files/144316/original/image-20161103-27234-146ojxx.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=532&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/144316/original/image-20161103-27234-146ojxx.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=532&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/144316/original/image-20161103-27234-146ojxx.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=668&fit=crop&dpr=1 754w, https://images.theconversation.com/files/144316/original/image-20161103-27234-146ojxx.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=668&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/144316/original/image-20161103-27234-146ojxx.gif?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=668&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 motion of Barnard’s star, one of the sun’s nearest neighbours, against background stars over a 20 year period.</span>
<span class="attribution"><span class="source">Steve Quirk</span></span>
</figcaption>
</figure>
<p>By observing the same star several times, Gaia can determine how it moves across the sky, giving us an incredibly <a href="http://www.astronomy.ohio-state.edu/%7Epogge/Ast162/Unit1/distances.html">precise measurement of the star’s distance from Earth</a>. Gaia also reveals <a href="http://www.atnf.csiro.au/outreach/education/senior/astrophysics/proper_motion.html">the kinematics of the stars</a> – how they move with respect to one another through our galaxy.</p>
<p>Even on its own, Gaia’s data will be an incredible resource. But when combined with data obtained by Galah and its siblings, it becomes far more powerful. Gaia will provide the distance to, and the precise motion of, a huge number of stars that will also have been surveyed by Galah. </p>
<h2>Our first steps</h2>
<p>The <a href="http://www.cosmos.esa.int/web/gaia/dr1">first public release</a> of Gaia data earlier this year included precise sky positions and brightnesses for more than a billion stars and quasars. More importantly for our work, it also included the distances and space motions for 2 million stars that had been targeted by previous space missions.</p>
<p>To coordinate with Gaia, Galah also made a subset of its data <a href="https://cloudstor.aarnet.edu.au/plus/index.php/s/OMc9QWGG1koAK2D">publicly available</a>, including data for 9,860 stars. Of these, 7,894 are in the special subset released by the Gaia team, and hence have precisely known distances.</p>
<p>Combining these data sets will allow the Galah team to investigate not just which stars formed together, but to examine whether they still follow similar paths around the galaxy. </p>
<p>As the Gaia mission continues, it will provide precise distances and space motions for every single star in the Galah catalogue. By piecing Gaia’s data together with our own, we will paint a far more detailed picture of our galaxy’s past, present and future than has ever been seen before.</p><img src="https://counter.theconversation.com/content/64887/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Sarah Martell receives funding from the Australian Research Council. </span></em></p><p class="fine-print"><em><span>Jonathan P. Marshall and Jonti Horner do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Understanding how the billions of stars in our galaxy formed and evolved is the subject of a huge galactic archaeology project.Jonti Horner, Vice Chancellor's Senior Research Fellow, University of Southern QueenslandJonathan P. Marshall, Vice Chancellor's Post-doctoral Research Fellow, UNSW SydneySarah Martell, Senior lecturer, UNSW SydneyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/673922016-10-21T14:39:24Z2016-10-21T14:39:24ZTo uncover the secrets of exoplanets, try listening to them<figure><img src="https://images.theconversation.com/files/142512/original/image-20161020-8849-9c8xs4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Truth is out there. </span> <span class="attribution"><a class="source" href="http://www.shutterstock.com/pic-143547211/stock-photo-planetary-nebulae-and-exoplanets.html?src=qpnXCTMizNCZmQIwNfl1NA-1-53">macro-vectors</a></span></figcaption></figure><p>From rainfall patterns to share price performance, the usual way to analyse any data that shows something changing over a period of time is to put it into a graphic. Making data visual usually makes it much easier to understand the trends – but not always. </p>
<p>When you’re trying to compare various datasets at the same time, for example, the X and Y axes of a graph quickly become limiting. Graphs are also often more useful for considered analysis in front of a computer than when you’re trying to follow something in real time. </p>
<p>A way around these problems is to convert the data into different pitches of sound. Known as sonification, this speeds up analysis by allowing listeners to compare multiple datasets simultaneously. And because the human ear <a href="http://www.economist.com/news/science-and-technology/21694992-scientific-data-might-be-filled-important-things-waiting-be-discovered">can detect</a> tiny changes in sound across a wide range of frequencies, we can often spot unexpected patterns much more easily by listening to data than looking at it. </p>
<p>In fact, we’ve been using sonification to study certain kinds of information for decades. Since the 1950s seismologists <a href="http://sonification.de/handbook/download/TheSonificationHandbook-chapter12.pdf">have been</a> using it to analyse earthquake data since it helps them discriminate between earthquakes and atomic explosions. <a href="https://www.rowinginmotion.com/listen-to-your-boat-effectively-using-sonification-in-rowing/">Meanwhile</a>, it is used in rowing to let rowers listen in real time to the smoothness of their stroke and adjust their technique accordingly. This has been successfully <a href="https://stephenbarrass.com/2009/06/21/sonification-of-rowing/">used by</a> Australian, German and Swedish Olympic crews, for example.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/YxWNw9fIizk?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
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<p>One area where sonification has not been used but has great potential is the study of exoplanets – planets that orbit stars other than our sun. We are developing a system for this and believe that in the coming decades it could make a huge difference to how well we understand worlds beyond our own. </p>
<h2>Space sound</h2>
<p><a href="http://cse.ssl.berkeley.edu/stereo_solarwind/sounds_links.html">Sonification</a> has been used in space research in the study of solar wind, <a href="https://smartech.gatech.edu/bitstream/handle/1853/49913/Alexanderetal2010.pdf">to establish</a> a much more accurate way of determining the origins of <a href="http://www.swpc.noaa.gov/phenomena/coronal-mass-ejections">coronal mass ejections</a>, which are major explosions of plasma and magnetic field from the sun. Probably the most memorable recent application in astronomy, however, has been <a href="https://theconversation.com/gravitational-waves-found-the-inside-story-54589">gravitational waves</a>, whose existence was demonstrated through sound. Professor Brian Greene, who led the discovery, <a href="http://theweek.com/speedreads/608331/physicist-brian-greene-clearly-joyfully-explains-gravitational-waves-stephen-colbert">said sonification was</a> “the future of studying the cosmos” and the only way of discerning certain aspects of the universe. </p>
<p>Our project <a href="http://www.iidi.napier.ac.uk/c/publications/publicationid/13385644">initially focused</a> on sonifying our solar system, but is now concerned with applying the technique to exoplanets, including their mass, size, movement, speed of movement, axis tilt, atmospheric conditions and the chemical properties of their atmospheres. Our work suggests that sonifying these sets of data makes it easier and faster to recognise interesting patterns. </p>
<p>So how would this work? Over the next couple of years we will be building a surround-sound environment to enable listeners to “stand” in the centre of a given <a href="https://soundcloud.com/michael-quinton_napier/the-solar-system">solar system</a>. By listening to the data from the various orbits of the planets, astronomers will be able to determine the speeds at which exoplanets are travelling and the gravitational effects when exoplanets align, among other things.</p>
<p>They will be able to hear variances due to natural distortion that occurs when two sounds interact in the same space – as you can hear below from a clip of sonification work we did on the four inner planets in our solar system. </p>
<iframe width="100%" height="450" scrolling="no" frameborder="no" src="https://w.soundcloud.com/player/?url=https%3A//api.soundcloud.com/tracks/275281338&auto_play=false&hide_related=false&show_comments=true&show_user=true&show_reposts=false&visual=true"></iframe>
<p>By integrating the sound data from the parent star, astronomers will be able to hear differences between a dip or gain in solar output. This would make it easier to determine whether it was caused by a solar flare or by a planet passing. </p>
<p>It might also be possible to find evidence of undiscovered planets in a solar system by hearing their gravitational influence through unexpected sounds in the orbits or atmospheric data of other planets in a system. Astronomers would then be able to point a telescope in the right direction to try to find the source.</p>
<h2>Exo in unison</h2>
<p>Sonification could also be used to compare various solar systems by multi-layering their datasets. Once astronomers “listened” to a number of systems in unison, they would get used to a particular sonic signature for each one from the sum of the sounds of the solar activity and planets within the system. Anomalies and differences would help draw attention to trends. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/142518/original/image-20161020-8869-1y5gguy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/142518/original/image-20161020-8869-1y5gguy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/142518/original/image-20161020-8869-1y5gguy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/142518/original/image-20161020-8869-1y5gguy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/142518/original/image-20161020-8869-1y5gguy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/142518/original/image-20161020-8869-1y5gguy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/142518/original/image-20161020-8869-1y5gguy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/142518/original/image-20161020-8869-1y5gguy.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">We have you in our sights, Planet X.</span>
<span class="attribution"><a class="source" href="http://www.shutterstock.com/pic-135864119/stock-photo-abstract-space-stars-futuristic-new-age-background.html?src=MUFvnFcOXe53kgNtGgw4vw-2-7">pixelparticle</a></span>
</figcaption>
</figure>
<p>Astronomers would also be able to save time by going through large amounts of data simultaneously. We are seeing a sharp increase in the discovery of exoplanets, which means there are more and more sets of data to handle. This year alone, about 1,000 new planets have been added to the <a href="http://exoplanetarchive.ipac.caltech.edu">database</a> – and the rate of discovery is <a href="https://carnegiescience.edu/news/new-tool-refines-exoplanet-search">likely to</a> rise further in the near future as detection techniques keep improving. </p>
<p>In short, sonification has huge potential in deepening our understanding of exoplanets across the universe. In years to come it should become an additional tool for revealing the secrets beyond our solar system. We like to say that seeing is believing, but hearing could be the key to truly understanding our universe.</p><img src="https://counter.theconversation.com/content/67392/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 organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Sonification is a technique for converting data into sound. It could transform the study of distant worlds.Michael Quinton, Pre-Doctoral Researcher, Edinburgh Napier UniversityDavid Benyon, Professor of Computing, Edinburgh Napier UniversityDr Iain McGregor, Lecturer in Sound Design, Edinburgh Napier UniversityLicensed as Creative Commons – attribution, no derivatives.