tag:theconversation.com,2011:/ca/topics/solar-eclipse-2017-41449/articlesSolar eclipse 2017 – The Conversation2017-08-22T19:18:03Ztag:theconversation.com,2011:article/828252017-08-22T19:18:03Z2017-08-22T19:18:03ZWhat blackout? How solar-reliant power grids passed the eclipse test<p>The total solar eclipse that captivated the United States this week was more than just a celestial spectacle (and a reminder to <a href="http://www.abc.net.au/news/2017-08-22/donald-trump-looks-at-eclipse-without-glasses/8830404">take care of your eyes</a>). It was also a valuable lesson in how to manage electricity grids when a crucial generation source – solar power, in this case – goes temporarily offline.</p>
<p>The last total solar eclipse to pass over the US was <a href="http://abcnews.go.com/US/back-1979-total-solar-eclipse/story?id=49310831">in 1979</a>, a year when President Jimmy Carter was in the midst of the energy crisis and struggling with ballooning oil prices. In response, he made a concerted shift to greater energy independence through alternative energy sources such as solar.</p>
<p>In 2017, almost the whole world is grappling with the transformation of the electricity industry and the move to renewable energy.</p>
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<a href="https://theconversation.com/scientist-at-work-why-this-meteorologist-is-eager-for-an-eclipse-80636">Scientist at work: Why this meteorologist is eager for an eclipse</a>
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<p>Eclipses have – and always will have – a lot to teach us. While this eclipse <a href="https://www.ft.com/content/d5119962-868f-11e7-8bb1-5ba57d47eff7">did not cause major disruption to the US electricity network</a>, it gave system operators a better understanding of how future intermittencies can be managed. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/182901/original/file-20170822-22150-52997z.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/182901/original/file-20170822-22150-52997z.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/182901/original/file-20170822-22150-52997z.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=334&fit=crop&dpr=1 600w, https://images.theconversation.com/files/182901/original/file-20170822-22150-52997z.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=334&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/182901/original/file-20170822-22150-52997z.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=334&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/182901/original/file-20170822-22150-52997z.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=420&fit=crop&dpr=1 754w, https://images.theconversation.com/files/182901/original/file-20170822-22150-52997z.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=420&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/182901/original/file-20170822-22150-52997z.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=420&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">The path of the eclipse, shown relative to the positions of major US solar power installations.</span>
<span class="attribution"><span class="source">US Energy Information Administration</span></span>
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<p>Despite the rapid decline and rebound in solar power output during the event, operators were able to manage without a hitch. Their thankless task reminds us of the importance of having resilient and robust electricity systems with sufficient backup capacity.</p>
<p>Solar plants lost around half of their ability to generate electricity during the two and a half hours of the eclipse, dipping and rising almost three times faster than the average rate at which power stations can ramp their output up and down. The shortfall was covered largely by gas-fired power plants, and extra hydro capacity.</p>
<p>California faced a particularly tough challenge because of its relatively high level of renewable energy; last year 10% of the state’s electricity came from solar photovoltaic (PV) power.</p>
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<img alt="" src="https://images.theconversation.com/files/182918/original/file-20170822-3806-12dwcxr.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/182918/original/file-20170822-3806-12dwcxr.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=408&fit=crop&dpr=1 600w, https://images.theconversation.com/files/182918/original/file-20170822-3806-12dwcxr.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=408&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/182918/original/file-20170822-3806-12dwcxr.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=408&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/182918/original/file-20170822-3806-12dwcxr.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=512&fit=crop&dpr=1 754w, https://images.theconversation.com/files/182918/original/file-20170822-3806-12dwcxr.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=512&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/182918/original/file-20170822-3806-12dwcxr.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=512&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">California’s solar output during the eclipse.</span>
<span class="attribution"><span class="source">California ISO</span></span>
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<p>Given the <a href="https://theconversation.com/au/topics/national-electricity-market-2810">recent scrutiny</a> on Australia’s <a href="https://theconversation.com/australias-energy-sector-is-in-critical-need-of-reform-61802">beleaguered electricity grid</a>, it makes sense to ask how our power system would fare if faced with the same challenge. Take a walk through almost any suburb and you’ll see dozens of solar panels glinting from roofs. How much have they destabilised our grid? Would we pass the eclipse test?</p>
<p>System managers and market operators such as the <a href="https://www.aemo.com.au/">Australian Energy Market Operator</a> already intricately balance demand and supply levels throughout the day, and must deal with unexpected outages at power stations, extreme weather events (think of <a href="https://theconversation.com/what-caused-south-australias-state-wide-blackout-66268">South Australia</a>), and increasingly predict how the share of intermittent generation from renewable resources will be matched and secured.</p>
<p>According to the <a href="https://www.cleanenergycouncil.org.au/cec.html">Clean Energy Council</a>, Australian renewables <a href="https://www.cleanenergycouncil.org.au/policy-advocacy/reports/clean-energy-australia-report.html">provided 17% of the country’s electricity generation in 2016</a>. In world terms that looks rather unimpressive. But this figure does not reflect the growing impact of behind-the-meter solar PV that is slowly but surely reducing reliance on grid electricity during the day. </p>
<p>As outlined in a previous <a href="https://theconversation.com/factcheck-qanda-is-australia-the-world-leader-in-household-solar-power-56670">FactCheck</a>, Australia has the highest proportion of households with PV systems on their roof of any country in the world, at over 15%. (However our total energy produced from solar is somewhat less than Germany, Italy, Belgium and Japan, which have a propensity for larger systems). </p>
<p>Of course, all this distributed solar adds to the complexity for utilities and grid operators, and underpins why we have technical rules and connection standards to ensure that households connecting individual systems to the grid do not cause unintended consequences for local network areas. As the forecasts for rooftop solar installations continue to be revised upwards, AEMO nevertheless <a href="https://www.aemo.com.au/Electricity/National-Electricity-Market-NEM/Planning-and-forecasting/Electricity-Forecasting-Insights/Key-component-consumption-forecasts/PV-and-storage">remains sanguine about the potential for grid disruption</a>:</p>
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<p>…it is technically feasible to integrate this amount of rooftop PV into the network over the forecast horizon, through a mix of market, network, and non-network (such as storage) solutions to address issues such as increasing variability in system demand, low daytime demand, and increased ramping at morning and afternoon electricity system peaks.</p>
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<p>Utilities themselves are acutely aware of the “non-negotiable social contract of keeping the lights on”, as mused by Frank Tudor, chief executive of Western Australia’s regional utility Horizon Power, in an <a href="https://www.linkedin.com/pulse/mondays-solar-eclipse-frank-tudor">opinion piece</a> written before the eclipse. The emboldened South Australian government may take further comfort in the fact that its newly minted <a href="http://www.afr.com/business/energy/electricity/solar-reserve-to-build-new-650m-solar-thermal-plant-in-sa-20170814-gxvu2m">150-megawatt Aurora Solar Energy Project</a> would come into its own during such weather interruptions (more often due to clouds than eclipses), with its capacity to store solar power in molten salt storage tanks, to be dispatched as required during peak periods.</p>
<h2>Lean and green machines</h2>
<p>The eclipse also underlines how crucial the innovations in technology and data analytics will be in ensuring that electricity grids can still operate seamlessly as the share of renewable energy grows.</p>
<p>We are seeing this already in many small, isolated power networks across the country, where <a href="https://horizonpower.com.au/our-community/news-events/news/wa-leads-the-way-in-energy-transformation/">microgrids</a>, particularly in coastal tourist towns with a proclivity for clean technology, are already pushing the limits of hosting capacity and driving utilities to explore big data solutions to assist with the integration of increased levels of solar PV.</p>
<p>One such example is the <a href="https://horizonpower.com.au/carnarvon-distributed-energy-resources-der-trial/">sky camera trial</a> being conducted in Carnarvon, Western Australia, that will track weather patterns and anticipate cloud cover to help with grid stability. The trial is using machine learning to help predict the impact of weather on the grid, and to balance the fluctuations with other energy sources, thus helping the network to withstand such events without losing reliability.</p>
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Read more:
<a href="https://theconversation.com/five-things-the-east-coast-can-learn-from-wa-about-energy-76398">Five things the east coast can learn from WA about energy</a>
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<p>With our energy systems becoming ever more distributed and decentralised, the US eclipse provides another of nature’s lessons on the need to be smart about creating resilient networks.</p>
<p>The next <a href="http://www.abc.net.au/news/2017-08-22/total-solar-eclipse-when-where-australia/8813250">total solar eclipse for Australia</a> will be in 2028, and will pass straight over Sydney. In the meantime, a <a href="https://www.timeanddate.com/eclipse/hybrid-solar-eclipse.html">hybrid eclipse</a> will cross Australia’s northwest in <a href="https://www.timeanddate.com/eclipse/solar/2023-april-20">April 2023</a>. </p>
<p>Time will tell how much of an impact these events will have on our power grids. But given the importance of electricity for our health, wealth, transport and so much more, let’s hope our system operators and policy makers aren’t blindsided.</p><img src="https://counter.theconversation.com/content/82825/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Dev Tayal also works as a strategist for Horizon Power.</span></em></p>The solar eclipse offered electricity network operators a “live drill” in how to cope with fluctuating output from renewable energy. They passed with flying colours.Dev Tayal, Energy Researcher, Curtin UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/798872017-08-17T01:28:03Z2017-08-17T01:28:03ZHow ancient cultures explained eclipses<figure><img src="https://images.theconversation.com/files/182303/original/file-20170816-10024-1ucrul3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A 1765 painting of Helios, the personification of the sun in Greek mythology.</span> <span class="attribution"><a class="source" href="https://upload.wikimedia.org/wikipedia/commons/6/61/Mengs%2C_Helios_als_Personifikation_des_Mittages.jpg">Wikimedia Commons</a></span></figcaption></figure><p>On April 8, 2024, a total solar eclipse will be visible across parts of the U.S.</p>
<p>As the Earth and moon sweep through space in their annual journey around the sun, the three bodies align in such a way that the Earth passes into the shadow of the moon. Observers then witness a sun that is gradually covered and uncovered by the moon’s disk – a spectacular celestial event.</p>
<p>But until astronomers were able to <a href="https://theconversation.com/when-the-sun-goes-dark-5-questions-answered-about-the-solar-eclipse-81308">explain this phenomenon</a>, a solar eclipse could be a terrifying event. In many cultures throughout human history, the sun was seen as an entity of supreme importance, crucial to their very existence. It was regularly worshipped as a god – <a href="http://www.ancient.eu/amun/">Amun-Ra</a> to the Egyptians and <a href="https://www.greekmythology.com/Other_Gods/Helios/helios.html">Helios</a> to the Greeks – or as a goddess, such as <a href="http://www.enryo.ro/carti/Japanese%20mythology%20A%20to%20Z.pdf">Amaterasu</a> for the Japanese and <a href="https://www.britannica.com/topic/Saule">Saule</a> for many Baltic cultures.</p>
<p>One reason the sun served as a god or goddess in so many cultures was its awesome power: Looking directly at it would severely damages the eyes, a sign of the sun deity’s wrath.</p>
<p>So the idea that the sun deity could be temporarily extinguished in a total eclipse inspired a number of imaginative explanations. Most involve some sort of evil entity trying to devour the sun. Such myths undoubtedly arose from the fact that during the early stages of a solar eclipse, the sun appears to have a bite taken out of it.</p>
<p>The various creatures include the Vikings’ <a href="http://norse-mythology.org/skoll-hati/">sky wolves Skoll and Hati</a>, a Chinese dragon, a Vietnamese frog and assorted Roman demons. In many cultures, it was believed that such creatures could be driven off <a href="http://www.exploratorium.edu/eclipse-archive/dragon.html">by creating as much loud noise as possible</a>: yelling, ringing bells, and banging pots and pans. </p>
<p>Perhaps the most creative version of this strand of mythologies comes from certain branches of Hindu culture. <a href="http://www.nationalgeographic.com/news/2013/11/131101-solar-eclipse-myth-legend-space-science">In that version</a>, the mortal Rahu is said to have attempted to attain immortality. The sun and moon told the god Visnu of Rahu’s transgression. As punishment, Visnu decapitated Rahu. </p>
<p>Ever since, Rahu has sought to exact vengeance on the sun and the moon by pursuing them across the sky to eat them. Once in a while – at the time of an eclipse – Rahu actually catches the sun or the moon. In the case of a solar eclipse, Rahu slowly devours the sun, and it gradually disappears into Rahu’s throat – only to reappear from his severed neck. </p>
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<a href="https://images.theconversation.com/files/182304/original/file-20170816-32640-1buwtpf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/182304/original/file-20170816-32640-1buwtpf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/182304/original/file-20170816-32640-1buwtpf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=451&fit=crop&dpr=1 600w, https://images.theconversation.com/files/182304/original/file-20170816-32640-1buwtpf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=451&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/182304/original/file-20170816-32640-1buwtpf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=451&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/182304/original/file-20170816-32640-1buwtpf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=567&fit=crop&dpr=1 754w, https://images.theconversation.com/files/182304/original/file-20170816-32640-1buwtpf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=567&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/182304/original/file-20170816-32640-1buwtpf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=567&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Rahu swallowing the moon.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/64337707@N07/10684670235">Anandajoti Bhikkhu</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
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<p>In other branches of Hindu culture, the “sun eater” took the more traditional form of a dragon. To fight this beast, certain Hindu sects in India <a href="https://www.washingtonpost.com/graphics/2017/lifestyle/eclipse-myths/?utm_term=.c161179514f9">immersed themselves up to the neck in water</a> in an act of worship, believing that the adulation would aid the sun in fighting off the dragon. </p>
<p>Other cultures had equally ingenious explanations for – and defenses against – a total solar eclipse. <a href="http://www.pitara.com/non-fiction-for-kids/features-for-kids/myths-legends-related-to-eclipses">Eskimos thought</a> an eclipse meant that the sun and moon had become temporarily diseased. In response, they’d cover up everything of importance – themselves included – lest they be infected by the “diseased” rays of the eclipsed sun. </p>
<p><a href="https://www.theatlantic.com/science/archive/2017/08/kings-beware-the-eclipse-looms/536385/">For the Ojibwe tribe of the Great Lakes</a>, the onset of total eclipse represented an extinguished sun. To prevent permanent darkness, they proceeded to fire flaming arrows at the darkened sun in an attempt to rekindkle it. </p>
<p>Amidst the plethora of the myths and legends and interpretations of this strange event, there are seeds of understanding about their true nature.</p>
<p>For example, the famed total solar eclipse of May 28, 585 B.C., occurred in the middle of a battle between the Medes and the Lydians in what is now the northeast region of modern-day Turkey. <a href="https://www.wired.com/2008/05/may-28-585-bc-predicted-solar-eclipse-stops-battle/">The eclipse actually ended the conflict on the spot</a>, with both sides interpreting the event as a sign of the displeasure from the gods. But based on the writings of the ancient Greek historian Heroditus, it’s thought that the great Greek philosopher-mathematician Thales of Miletus had, coincidentally, <a href="http://adsabs.harvard.edu/full/1994JHA....25..275P">predicted its occurrence</a>. </p>
<p>Chinese, Alexandrian and Babylonian astronomers <a href="http://www.bibalex.org/eclipse2006/HistoricalObservationsofSolarEclipses.htm">were also said to be sophisticated enough</a> to not only understand the true nature of solar eclipses, but also to roughly predict when the “dragon” would come to devour the sun. (As with much knowledge back then, however, astronomical and astrological findings were relayed only to the ruling elites, while myths and legends continued to percolate among the general population.)</p>
<p>Advances in modern astronomy have given us detailed explanations for solar eclipses, to the extent that their time and location can be predicted centuries into the future and reconstructed from centuries ago.</p>
<p>Of course, mythologies surrounding total solar eclipses still exist today. Some conspiracy theorists <a href="http://www.dailymail.co.uk/sciencetech/article-4767852/Will-September-s-solar-eclipse-cause-world-end.html">were convinced that a 2017 eclipse would spell the end of the world</a> – perhaps a testament to the endurance of the superstitious side of the human psyche.</p><img src="https://counter.theconversation.com/content/79887/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Roger Culver 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>The sun was worshiped as a deity in many cultures – and witnessing it get extinguished could be a particularly terrifying event.Roger Culver, Emeritus Professor of Physics, Colorado State UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/810672017-08-16T23:20:00Z2017-08-16T23:20:00ZHow to safely watch an eclipse: Advice from an astronomer<figure><img src="https://images.theconversation.com/files/181473/original/file-20170808-26021-1c1hxx.jpg?ixlib=rb-1.1.0&rect=35%2C0%2C1455%2C920&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A total solar eclipse will be visible across parts of the United States Aug. 21, treating amateur and professional astronomers alike to sights similar to this NASA's Solar Dynamics Observatory ultraviolet image of the moon eclipsing the sun on Jan. 31, 2014.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/sdomission/12240009064/in/photolist-jDBfg3-c2E1bq-dtBfWJ-dtvHND-c31tsQ-fK6r7i-p3CWN2-p3zyq3-pGZ1wS-pXgLpy-pH2M45-pZnpn8-pXgTbQ-pH3Cd7-s5MMYH-pZvjy1-pZviTU-pGWFJr-pXgK4s-pXgSzj-p3D4wH-pZcvmt-pZnzyk-pZnxjk-p3Cqpg-c2xmSf-6GZ5Pf-6GUVQ4-oU2ZbY-6GZ9uo-6GZBA2-6GUnbM-6H58jj-6H5raG-6GYFFy-6H1mrn-6GZgJ3-6H5hUC-6GZJmZ-6H4SYb-6GZCHF-6H1jW2-6GZjY3-6H5mYb-6H4Vwh-6H4Uhq-qNsbs1-89mqGm-6GZMbV-6H59P1/">(NASA)</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span></figcaption></figure><p>Everyone knows that you should not look at the sun!</p>
<p>Not with your naked eye, not with sunglasses and certainly not with binoculars or with a telescope. Our sun might be just an ordinary star, but it’s extremely close to us — about 269,000 times closer than the <a href="https://imagine.gsfc.nasa.gov/features/cosmic/nearest_star_info.html">next nearest star</a>. This makes the sun very, very bright.</p>
<p>Everyone knows that you should not look at the sun. But what about during an eclipse? This situation will confront us <a href="http://eclipse.aas.org">on Aug. 21</a>, when the entirety of North America, along with parts of South America, Africa, Europe and eastern Russia, will experience a solar eclipse.</p>
<p>For the vast majority of viewers, including anyone in any part of Canada, the eclipse will be a <a href="https://www.timeanddate.com/eclipse/partial-solar-eclipse.html">partial one</a>. This means that the moon will block out part of the face of the sun but leave the rest of it unchanged.</p>
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<a href="https://images.theconversation.com/files/181475/original/file-20170808-26048-o6es2t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/181475/original/file-20170808-26048-o6es2t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/181475/original/file-20170808-26048-o6es2t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/181475/original/file-20170808-26048-o6es2t.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/181475/original/file-20170808-26048-o6es2t.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/181475/original/file-20170808-26048-o6es2t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/181475/original/file-20170808-26048-o6es2t.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/181475/original/file-20170808-26048-o6es2t.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">NASA’s Solar Dynamics Observatory saw a partial solar eclipse in space when it caught the moon passing in front of the sun on May 25, 2017.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/nasamarshall/35568871254/in/photolist-Wc6LdW-WNjGWq-pMH5pg-6H2N8P-bUewyv-97Gehi-cbVVVm-Wgbiyu-RRJNpz-c2ZUhU-yA7gAy-9ZGcuR-S297WM-97pycE-vhGtc-97py8J-c1aCmd-hDBUv-6HqTa5-6N8pS5-97ncbx-pMPDra-c2Hp5A-r2yLWw-8GrzH8-c2ABNC-dKAnj3-8GryAM-6H2YYW-c2BzP7-eTkScd-c2AnGw-dtdZj6-8GrykF-emmsJ-c2AmK9-8GuNfy-c2Cqxw-c2AmBN-8GuNJY-8GuKWf-8GuMfC-c2Az8C-c2LXFA-97mQhT-qHr81h-c2Arkw-c2Azjj-8NxqFU-c2AqXo">(NASA)</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>If you’re under <a href="https://eclipse.gsfc.nasa.gov/SEanimate/SEanimate2001/SE2017Aug21T.GIF">the path of the partial eclipse</a> — even somewhere where the sun is 99 per cent concealed — you still should not look at the sun with the unaided eye. Even one-hundredth of the sun’s normal brightness is enough to permanently damage your eyesight.</p>
<p>Instead, you can safely watch the action through special <a href="https://www.space.com/36941-solar-eclipse-eye-protection-guide.html">eclipse glasses</a> (make sure they’re <a href="https://eclipse.aas.org/eye-safety/iso-certification">ISO certified and from a reliable supplier</a>), through a simple <a href="https://www.jpl.nasa.gov/edu/learn/project/how-to-make-a-pinhole-camera/">home-made pinhole camera</a> or even by looking at the shadows cast by <a href="https://petapixel.com/2012/05/21/crescent-shaped-projections-through-tree-leaves-during-the-solar-eclipse/">tree leaves</a> or by a <a href="http://www.huffingtonpost.co.uk/2015/03/20/solar-eclipse-colander-_n_6908140.html">kitchen colander</a>.</p>
<p>For some lucky viewers in parts of <a href="http://eclipse2017.org/blog/2017/01/15/states-the-total-eclipse-touches/">14 U.S. states</a>, a total solar eclipse awaits on Aug. 21. This will be far more exciting than a mere partial eclipse. For maybe as long as two minutes, depending on your exact location, the sun will disappear completely behind the moon. The temperature will drop, the stars will come out, and the birds will think evening has come.</p>
<p>If you are under the path of the total eclipse, you’ll likely have more than an hour of partial eclipse both before and after the exciting moment of totality. During the partial phases, the usual rules apply: Wear your eclipse glasses or use your colander, but don’t look at the sun unaided!</p>
<p>However, when the time finally arrives and when the sky goes dark, it will finally be safe to look. Take off your glasses, stare at the sun with your unaided eyes, and soak up a remarkable cosmic moment.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/181476/original/file-20170808-26004-1qtloh3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/181476/original/file-20170808-26004-1qtloh3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=402&fit=crop&dpr=1 600w, https://images.theconversation.com/files/181476/original/file-20170808-26004-1qtloh3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=402&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/181476/original/file-20170808-26004-1qtloh3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=402&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/181476/original/file-20170808-26004-1qtloh3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=505&fit=crop&dpr=1 754w, https://images.theconversation.com/files/181476/original/file-20170808-26004-1qtloh3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=505&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/181476/original/file-20170808-26004-1qtloh3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=505&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The Hinode satellite observed the sun’s corona during a total solar eclipse on July 22, 2009.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/nasamarshall/3749824749/in/photolist-6HmQfR-amTUw8-ffnGgr-c2KEsh-87puxz-uoX4dq-6GZssa-W33piE-6GXKhS-6GZKUc-USp1ay-6H4x5u-na8q4i-aTdLfT-6GUbft-c2Ah4G-6GZwRv-6GYR9h-c2AiB3-6GTKSM-voESN-6GZuCB-97whBh-6H4CHW-pKwfEf-6GVhxv-c2AhrE-c2AiY7-pMEk4M-hFGgPZ-6GZZFa-pMJAnw-pMqArp-bo72po-pMEjHr-qfriq-hFDv8-9ogkg7-c2Ynk5-6H52Go-pvdsTL-c2Ak3j-LLRtM-6GYNzS-c2AjRE-59vsFe-4ZKxAs-6GYTMo-hFGggK-6SFStG">(NASA/JAXA)</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<p>During the total eclipse, it is completely safe to look at the sun without any equipment at all. And what a sight it will be.</p>
<p>Revealed, just for a moment, will be <a href="https://www.exploratorium.edu/eclipse/what-to-see-during-eclipse#totality">the sun’s glorious corona</a>, the faint <a href="https://eclipse2017.nasa.gov/solar-corona">tendrils of ultra-hot gas</a> that stream off the sun’s blazing surface. This is not to be missed. If you leave your eclipse glasses on, you won’t see anything.</p>
<p>After a minute or two, the total eclipse will be over, the skies will lighten and special safety precautions must once again be taken. But those who experience totality will be left with memories of an otherwise hidden view of the Universe, a brief glimpse of our life-giving sun unlike any other.</p><img src="https://counter.theconversation.com/content/81067/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Bryan Gaensler receives funding from the Natural Sciences and Engineering Research Council of Canada and from the Canada Research Chairs Program. He is the Director of the Dunlap Institute for Astronomy and Astrophysics, which will be distributing its eclipse glasses free of charge at the Canadian National Exhibition and other events.</span></em></p>If you’ve ever wondered why you can look at a solar eclipse and why it can harm your eyes, the answer is in the sun’s rays.Bryan Gaensler, Director, Dunlap Institute for Astronomy and Astrophysics, University of TorontoLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/795532017-08-14T17:16:57Z2017-08-14T17:16:57ZTotal eclipse, partial failure: Scientific expeditions don’t always go as planned<figure><img src="https://images.theconversation.com/files/181829/original/file-20170811-13490-1ybkdxu.jpg?ixlib=rb-1.1.0&rect=415%2C944%2C5419%2C3587&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Have telescopes, will travel: English astronomers await an 1871 eclipse in India. </span> <span class="attribution"><span class="source">The Illustrated London News, 1872</span></span></figcaption></figure><p>For centuries, astronomers have realized that total solar eclipses offer a valuable scientific opportunity. During what’s called totality, the opaque moon completely hides the bright photosphere of the sun – its thin surface layer that emits most of the sun’s light. An eclipse allows astronomers to study the sun’s colorful outer atmosphere and its delicate extended corona, ordinarily invisible in the dazzling light of the photosphere.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/181868/original/file-20170813-13505-e765rp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/181868/original/file-20170813-13505-e765rp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/181868/original/file-20170813-13505-e765rp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/181868/original/file-20170813-13505-e765rp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/181868/original/file-20170813-13505-e765rp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/181868/original/file-20170813-13505-e765rp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/181868/original/file-20170813-13505-e765rp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/181868/original/file-20170813-13505-e765rp.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">With most of the sun’s light blotted out, an eclipse lets astronomers see some of its dimmer extended features.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/mission_pages/hinode/solar_020.html">NASA</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>But total solar eclipses are infrequent, and are visible only from a narrow path of totality. So eclipse expeditions require meticulous advance planning to ensure that astronomers and their equipment wind up in the right place at the right time. As the history of astronomy shows, things don’t always go according to plan for even the most prepared eclipse hunters.</p>
<h2>Into hostile territory, at the mercy of the map</h2>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/181810/original/file-20170811-13476-18oro9s.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/181810/original/file-20170811-13476-18oro9s.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/181810/original/file-20170811-13476-18oro9s.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=821&fit=crop&dpr=1 600w, https://images.theconversation.com/files/181810/original/file-20170811-13476-18oro9s.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=821&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/181810/original/file-20170811-13476-18oro9s.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=821&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/181810/original/file-20170811-13476-18oro9s.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1032&fit=crop&dpr=1 754w, https://images.theconversation.com/files/181810/original/file-20170811-13476-18oro9s.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1032&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/181810/original/file-20170811-13476-18oro9s.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1032&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Samuel Williams was prepared to cross enemy lines to see his eclipse.</span>
<span class="attribution"><span class="source">New England magazine, 1895</span></span>
</figcaption>
</figure>
<p>Samuel Williams, the newly appointed professor of mathematics and natural philosophy at Harvard College, was eager to observe a total solar eclipse. He’d seen a <a href="https://www.jstor.org/stable/1005194?seq=1#page_scan_tab_contents">transit of Venus in 1769</a>, but had never had the chance to study the sun’s corona during an eclipse. According to his calculations, a total solar eclipse would be visible from Maine’s Penobscot Bay on Oct. 27, 1780. </p>
<p>But reaching Maine from Massachusetts would be something of a problem; the Revolutionary War was raging, and Maine was held by the British Army. The Massachusetts legislature came to Williams’ assistance; it directed the state’s Board of War to fit out a ship to convey the eclipse hunters. Speaker of the House John Hancock wrote to the British commander in Maine, requesting permission for the men of science to make their observations. When the astronomer-laden ship arrived at Penobscot Bay, Williams and his team were permitted to land but restricted to the island of Isleboro, three miles offshore from the mainland.</p>
<p>The morning of the big day was cloudless. As the calculated moment of totality approached, at half past noon, the excitement built. The sliver of uneclipsed sun became narrower and narrower.</p>
<p>Then, at 12:31 p.m., it started becoming wider and wider. Williams realized, to his frustration, that he wasn’t in the path of totality after all. They were 30 miles too far south.</p>
<p>After a subdued voyage back to Massachusetts, Williams tried to determine what had gone wrong. Some astronomers, at the time and in following centuries, suggested his calculations of the path of totality were inaccurate.</p>
<p>Williams, however, had a different explanation. In his report to the newly founded American Academy of Arts and Sciences, he blamed <a href="https://www.jstor.org/stable/25053743?seq=22#page_scan_tab_contents">bad maps</a>:</p>
<blockquote>
<p>“The longitude of our place of observation agrees very well with what we had supposed in our calculations. But the latitude is near half a degree less than what the maps of that country had led us to expect.”</p>
</blockquote>
<p>Since half a degree of longitude corresponds to 30 nautical miles, this could explain why Williams ended up too far south.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/181813/original/file-20170811-13451-whylzh.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/181813/original/file-20170811-13451-whylzh.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/181813/original/file-20170811-13451-whylzh.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=480&fit=crop&dpr=1 600w, https://images.theconversation.com/files/181813/original/file-20170811-13451-whylzh.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=480&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/181813/original/file-20170811-13451-whylzh.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=480&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/181813/original/file-20170811-13451-whylzh.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=603&fit=crop&dpr=1 754w, https://images.theconversation.com/files/181813/original/file-20170811-13451-whylzh.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=603&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/181813/original/file-20170811-13451-whylzh.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=603&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Williams’ illustrations in his report of the eclipse. ‘Baily’s Beads’ are visible in Fig. VII on the upper right.</span>
<span class="attribution"><span class="source">Memoirs of the American Academy of Arts and Sciences</span></span>
</figcaption>
</figure>
<p>Although Samuel Williams missed seeing a total eclipse, his expedition was not a total failure. While watching the narrow sliver of sun visible at 12:31, he noted it became “broken or separated into drops.” These bright drops, known today as Baily’s Beads, are the result of the sun’s light shining through valleys and depressions along the moon’s visible edge. They’re named in honor of astronomer Francis Baily; however, <a href="https://doi.org/10.1093/mnras/4.2.15">Baily saw and described the beads in 1836</a>, nearly 56 years after Williams observed them. </p>
<h2>Hard to observe with smoke in your eyes</h2>
<p>Almost a century later, in 1871, English astronomer <a href="https://en.wikipedia.org/wiki/Norman_Lockyer">Norman Lockyer</a> was eager to observe a total solar eclipse.</p>
<p>Three years earlier, he and French astronomer <a href="https://en.wikipedia.org/wiki/Pierre_Janssen">Jules Janssen</a> had independently measured the spectrum of the sun’s chromosphere; to their surprise, they found an emission line in the yellow range of the spectrum, not corresponding to any known element.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/181870/original/file-20170813-13505-sxs6cw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/181870/original/file-20170813-13505-sxs6cw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/181870/original/file-20170813-13505-sxs6cw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=179&fit=crop&dpr=1 600w, https://images.theconversation.com/files/181870/original/file-20170813-13505-sxs6cw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=179&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/181870/original/file-20170813-13505-sxs6cw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=179&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/181870/original/file-20170813-13505-sxs6cw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=225&fit=crop&dpr=1 754w, https://images.theconversation.com/files/181870/original/file-20170813-13505-sxs6cw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=225&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/181870/original/file-20170813-13505-sxs6cw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=225&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 spectrum of helium: the bright yellow line at a wavelength of 587 nanometers (nm) is the emission line seen by Janssen and Lockyer.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Helium_spectrum.jpg">NASA</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Lockyer boldly claimed that the emission line was from a new element that he named “helium,” after the sun god Helios. Realizing that eclipses offered a helpful opportunity to search for more undiscovered elements, <a href="http://www.sup.org/books/title/?id=1216">Lockyer became a strong advocate of eclipse expeditions</a>. He knew the total solar eclipse of Dec. 12, 1871 would pass across southern India and persuaded the British Association for the Advancement of Science to sponsor an expedition. Wishing to show that British rule in India was linked to scientific progress, the British government chipped in £2,000, and the P&O steamship company offered reduced fares to India for the eclipse hunters.</p>
<p>Lockyer’s voyage to India went smoothly. (This could not be taken for granted; in 1870, on his way to view an eclipse from Italy, Lockyer was aboard a ship that ran aground off the east coast of Sicily.) The team set up their instruments on a tower at Bekal Fort, on the southwest Indian coast. The morning of Dec. 12, 1871 was cloudless. Although Lockyer was suffering from a fever (and from the effects of the opium he was taking to treat it), he was ready.</p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/181819/original/file-20170811-13483-ubydnp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/181819/original/file-20170811-13483-ubydnp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/181819/original/file-20170811-13483-ubydnp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=711&fit=crop&dpr=1 600w, https://images.theconversation.com/files/181819/original/file-20170811-13483-ubydnp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=711&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/181819/original/file-20170811-13483-ubydnp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=711&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/181819/original/file-20170811-13483-ubydnp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=894&fit=crop&dpr=1 754w, https://images.theconversation.com/files/181819/original/file-20170811-13483-ubydnp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=894&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/181819/original/file-20170811-13483-ubydnp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=894&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Artist’s sketch of the scene at Bekal as the eclipse gets underway.</span>
<span class="attribution"><span class="source">The Illustrated London News, 1872</span></span>
</figcaption>
</figure>
<p>Then, during the initial phases of the eclipse, he noted odd activity in the region below the fort. Local inhabitants were gathering a huge pile of brushwood to fuel a bonfire; apparently, by creating a bright fire on Earth, they hoped to encourage the darkening sun to become bright again. Lockyer was alarmed; the column of smoke would have risen directly between him and the eclipsed sun, ruining his observations.</p>
<p>Fortunately, the local superintendent of police happened to be present; he summoned a squadron of policemen who put out the fire and dispersed the crowd. During the now smoke-free eclipse, Lockyer made valuable observations of the structure of the sun’s corona.</p>
<h2>To see an eclipse you must see the sun</h2>
<p>Jump ahead to the early 20th century. The English Astronomer Royal <a href="http://adsabs.harvard.edu/full/1939Obs....62..179S">Sir Frank Dyson</a> was eager to view a total solar eclipse. He didn’t have to travel far, since the eclipse of June 29, 1927 had a path of totality cutting across northern England, from Blackpool in the west to Hartlepool in the east. As an eminent figure in the scientific establishment and a renowned expert on eclipses, Dyson had no trouble in commanding financial support for his eclipse observations.</p>
<p>What he could not command, however, was the famously fickle English weather. During the month of June, northern England averages about seven hours of direct sunlight per day; however, this comes from a mix of weather that includes completely overcast days and completely cloudless days. Dyson didn’t know what to expect.</p>
<p>After checking the weather records along the predicted eclipse path, Dyson decided to observe from the Yorkshire village of Giggleswick. As he and his team prepared for the eclipse, the location choice initially seemed dubious; for two weeks before the eclipse, the sky was completely cloudy every afternoon, at the time of day when totality would occur on June 29.</p>
<p>Despite the grimly unpromising weather, crowds of hopeful people converged on the widely publicized eclipse path. Railway companies ran special excursion trains, towns along the path of totality sponsored “eclipse dances” and newspapers offered “<a href="http://collection.sciencemuseum.org.uk/objects/co509985/ecliptoglass-eclipse-viewer-eclipse-viewer">ecliptoglasses</a>” to subscribers. </p>
<p>In the end, unfortunately, most viewers along the eclipse path were disappointed. From the errant cloud that blocked the totally eclipsed sun from Blackpool Tower to the unbroken overcast sky at Hartlepool, the weather did not cooperate. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/181816/original/file-20170811-13490-2phty2.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/181816/original/file-20170811-13490-2phty2.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/181816/original/file-20170811-13490-2phty2.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=466&fit=crop&dpr=1 600w, https://images.theconversation.com/files/181816/original/file-20170811-13490-2phty2.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=466&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/181816/original/file-20170811-13490-2phty2.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=466&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/181816/original/file-20170811-13490-2phty2.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=586&fit=crop&dpr=1 754w, https://images.theconversation.com/files/181816/original/file-20170811-13490-2phty2.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=586&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/181816/original/file-20170811-13490-2phty2.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=586&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">View of the totality at Gigglesworth, taken by Frank Dyson and his team.</span>
<span class="attribution"><a class="source" href="https://doi.org/10.1093/mnras/87.9.657">Plate 8, Report of the Expeditions from the Royal Observatory, Greenwich, to observe the Total Solar Eclipse of 1927 June 29. Astronomer Royal, Monthly Notices of the Royal Astronomical Society, Volume 87, Issue 9</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<p>Happily for Frank Dyson, however, the town of Giggleswick was nearly the only location along the eclipse path that had clear skies during totality. The estimated <a href="http://articles.adsabs.harvard.edu/full/1999JBAA..109..117M">70,000 people who converged there</a>, following the lead of the astronomer royal, also benefited from Dyson’s good luck.</p>
<p>After the eclipse, <a href="https://www.theguardian.com/science/1927/jun/30/eclipse1">Dyson’s public statement</a> was, by British standards, positively bubbly:</p>
<blockquote>
<p>“The photographs have come out extremely well. A very clear and striking eclipse. Our observations went off very well indeed.” </p>
</blockquote>
<p>Despite the difficulties posed by weather… and smoky bonfires… and dodgy maps… astronomers have always persevered in their quest to view eclipses.</p><img src="https://counter.theconversation.com/content/79553/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Barbara Ryden 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>For centuries, scientists have known when and where eclipses will be visible. They pack their bags, head for the line of totality and hope for the best – which doesn’t always happen.Barbara Ryden, Professor of Astronomy, The Ohio State UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/821712017-08-10T08:14:19Z2017-08-10T08:14:19ZWhat we can learn from the 2017 solar eclipse<figure><img src="https://images.theconversation.com/files/181212/original/file-20170807-29295-pk07yg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">名古屋太郎/wikimedia</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>If you’ve never seen a solar eclipse before, you should make an effort to witness the <a href="https://eclipse.gsfc.nasa.gov/SEgoogle/SEgoogle2001/SE2017Aug21Tgoogle.html">breathtaking event</a> on August 21. While only people in the US will be able to see the total eclipse – in which the moon completely blocks the light from the sun – those living in parts of South America, Africa and Europe should be able to see at least a partial solar eclipse.</p>
<p>Solar eclipses occur when the <a href="https://theconversation.com/explainer-what-is-a-solar-eclipse-33019">moon passes between the Earth and the sun</a> so that it blocks part or all of the sunlight as viewed from a particular location on our planet. Earth is the only planet in the solar system <a href="https://theconversation.com/when-the-sun-goes-dark-5-questions-answered-about-the-solar-eclipse-81308">where this can happen</a> in this way. This is because of the moon’s size and its relative distance from the sun – when viewed from the Earth, it can identically cover the bright solar disc to reveal the tenuous, wispy outer atmosphere of the star (called the solar corona). </p>
<p>An eclipse does not happen every time the moon travels around the Earth. This is because its orbit has a slight inclination (about five degrees) relative to our planet’s journey around the sun. However when aligned correctly, the result is an awesome, emotional experience. Once the eclipse has begun, the moon continues to eat its way across the blazing sun before darkness falls, the temperature drops and the sky is dominated by a radiant crown around the moon. It happens approximately every 18 months.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/179226/original/file-20170721-28515-1ep69w1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/179226/original/file-20170721-28515-1ep69w1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/179226/original/file-20170721-28515-1ep69w1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=408&fit=crop&dpr=1 600w, https://images.theconversation.com/files/179226/original/file-20170721-28515-1ep69w1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=408&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/179226/original/file-20170721-28515-1ep69w1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=408&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/179226/original/file-20170721-28515-1ep69w1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=513&fit=crop&dpr=1 754w, https://images.theconversation.com/files/179226/original/file-20170721-28515-1ep69w1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=513&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/179226/original/file-20170721-28515-1ep69w1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=513&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">During an eclipse the sun’s corona becomes visible to observers on Earth.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/sites/default/files/thumbnails/image/white_light_corona.jpg">NASA</a></span>
</figcaption>
</figure>
<p>On August 21, the moon’s shadow will travel west to east, touching land at Lincoln Beach, Oregon at 09:05 Pacific Daylight Time <a href="http://eclipse2017.nasa.gov/eclipse-live-stream">before speeding across</a> North America at up to 1km per second and finally exiting close to Charleston, South Carolina, at 16:09 Eastern Daylight Time. The longest total eclipse will occur close to the town of Carbondale, Illinois – lasting about two minutes and 40 seconds. </p>
<p>Anywhere within the 110km wide path of the eclipse, observers will be able to see the sun completely covered. Outside of that, sky-watchers will still see a partial eclipse with decreasing percentages of the sun’s surface covered as one moves away from this narrow corridor. It is estimated that over 12m Americans live in the path of the total eclipse itself and another 200m people within a day’s drive of it. This is science engagement on an unprecedented scale and is likely to be the most orchestrated eclipse viewing event ever undertaken.</p>
<h2>Digital deluge</h2>
<p>Social media activity has been increasing for months now, building up the anticipation to be part of this rare event. Expect Twitter, Facebook, Snapchat, Flickr and Instagram to be swamped with eclipse pictures during and after the event. In fact, the eclipse should be one of the most digitally recorded events ever, which could be of use to scientists. The <a href="http://eclipse2017.nso.edu/citizen-cate/">Citizen CATE</a> (Continental-America Telescopic Eclipse) experiment aims to capture images of the inner solar corona using a network of more than 60 telescopes operated by citizen scientists, high school groups and universities. </p>
<p>Similarly, the <a href="https://eclipsemega.movie/">Eclipse Mega-movie</a> is asking observers to use their app to upload eclipse images along the path of totality to produce an expanded and continuous film of the total eclipse as it crosses the country. Both of these experiments will produce unique data-sets of the <a href="http://www.oxfordreference.com/view/10.1093/oi/authority.20110803122316167">white light corona</a>, a region that is usually impossible to observe because the exceptionally bright solar disc hides it from view. We will be able to examine like never before the detailed structure of the solar corona and how it is dragged out into space by the solar wind.</p>
<p>There is also a big focus on education. A top priority is making sure that people know how to safely view the eclipse. Looking directly at the sun <a href="http://gizmodo.com/5926497/what-happens-when-you-stare-at-the-sun">is unsafe</a> except during that brief period of the total eclipse. It is vitally important that only special solar filters, <a href="https://eclipse2017.nasa.gov/safety">such as certified eclipse glasses</a>, are used. Unfiltered cameras, telescopes, binoculars or other optical devices concentrate the solar rays and are a definite no-go in regard to eye safety. If no filters are available, it is best to use a pinhole camera to project the eclipse indirectly.</p>
<p>It is also important to take advantage of the amazing opportunity to inform a huge population about the science behind the event. There are thousands of astronomy-oriented events, parties even, being hosted along the path of totality.</p>
<h2>New science?</h2>
<p>Scientists are equally excited. Eleven NASA and <a href="http://www.noaa.gov/">NOAA</a> satellites, high-altitude balloons, hundreds of ground-based telescopes and even the International Space Station will all take advantage of this unique shadow-chase across the surface of the Earth. However, it is not just looking up at the moon and sun that is important. Total eclipses also provide us with an unprecedented opportunity to examine our own planet under quite unusual conditions.</p>
<p>NASA says that observers across several states will measure the radiant energy from the sun into the Earth’s atmosphere from the ground as well as from space. This should provide new insights into how the incident solar energy in our atmosphere changes when particles, clouds and in this case the moon, prevents sunlight from reaching the surface of the planet.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/jzftVMQ78KU?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<p>I will be fortunate enough to be part of a four-hour live online telecast of the eclipse from Carbondale via NASA’s video podcast <a href="https://www.nasa.gov/multimedia/podcasting/nasaedge/index.html">EDGE</a>. This will include interviews with scientists and live panel questions, high-resolution sun images and a balloon launch. As a solar physicist who can only usually observe the solar corona from space by satellite instrumentation, it is special to be able to glimpse the corona with the (protected) naked eye for a brief time.</p>
<p>One interesting part to all this is the fact that the US gets another chance in seven years to maximise the opportunities that the eclipse brings. </p>
<p>It is said that one of the longlasting legacies of the Apollo missions to the moon is the number of American scientists today who were inspired to be engineers and scientists. Though this solar eclipse is science engagement in a different manner, the end goal is the same – bringing about not just a greater appreciation of the Earth, and solar or lunar research, but also sparking a desire in many young people to be the science leaders of the future.</p><img src="https://counter.theconversation.com/content/82171/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Robert William Walsh receives funding from the Science and Technology Facilities Council, UK.</span></em></p>The eclipse will be one of the most digitally recorded events ever. Here’s how to be part of it.Robert William Walsh, Professor of Solar Physics, University of Central LancashireLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/803092017-08-09T00:28:51Z2017-08-09T00:28:51ZEclipsing the occult in early America: Benjamin Franklin and his almanacs<figure><img src="https://images.theconversation.com/files/181273/original/file-20170807-2667-6m8q7c.jpg?ixlib=rb-1.1.0&rect=29%2C801%2C6501%2C5729&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Franklin's lifelong quest was spreading scientific knowledge to regular people.</span> <span class="attribution"><a class="source" href="http://www.loc.gov/pictures/item/2003674083/">Mason Chamberlin</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>By the time he was 20 years old, colonial American Benjamin Franklin had already spent two years working as a printer in London. He returned to Philadelphia in 1726. During the sea voyage home, he kept a journal that included many of his observations of the natural world. Franklin was inquisitive, articulate and <a href="http://www.pbs.org/benfranklin/l3_inquiring_weather.html">interested in mastering the universe</a>.</p>
<p>During one afternoon calm on September 14, Franklin wrote,</p>
<blockquote>
<p>“as we sat playing Draughts upon deck, we were surprised with a sudden and unusual darkness of the sun, which as we could perceive was only covered with a small thin cloud: when that was passed by, we discovered that that glorious luminary laboured under a very great eclipse. At least ten parts out of twelve of him were hid from our eyes, and we were apprehensive he would have been totally darkened.”</p>
</blockquote>
<p>Total solar eclipses are not rare phenomena; <a href="https://www.space.com/25644-total-solar-eclipses-frequency-explained.html">every 18 months</a> on average one occurs somewhere on Earth. Franklin and his shipmates likely had seen eclipses before. What was different for Franklin and his generation was a new understanding of the causes of eclipses and the possibility of accurately predicting them.</p>
<p>Earlier generations in Europe relied on magical thinking, interpreting such celestial events through the lens of the occult, as if the universe were sending a message from heaven. By contrast, Franklin came of age at a time when supernatural readings were held in suspicion. He would go on to spread modern scientific views of astronomical events through his popular almanac – and attempt to free people from the realm of the occult and astrological prophecy.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/181275/original/file-20170807-25556-188qjlc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/181275/original/file-20170807-25556-188qjlc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/181275/original/file-20170807-25556-188qjlc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=501&fit=crop&dpr=1 600w, https://images.theconversation.com/files/181275/original/file-20170807-25556-188qjlc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=501&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/181275/original/file-20170807-25556-188qjlc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=501&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/181275/original/file-20170807-25556-188qjlc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=629&fit=crop&dpr=1 754w, https://images.theconversation.com/files/181275/original/file-20170807-25556-188qjlc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=629&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/181275/original/file-20170807-25556-188qjlc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=629&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Ptolemy’s Earth-centered universe with the moon, Mercury, Venus, the sun, Mars, Jupiter and Saturn orbiting our planet.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Planisphaerium_Ptolemaicum_siue_machina_orbium_mundi_ex_hypothesi_Ptolemaica_in_plano_disposita_(2709983277).jpg">Andreas Cellarius</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>Beyond divine heavens with modern astronomy</h2>
<p>Ancient people conceived of the heavens as built around human beings. For centuries, people subscribed to the <a href="http://galileo.rice.edu/sci/theories/ptolemaic_system.html">Ptolemaic belief about the solar system</a>: The planets and the sun revolved around the stationary Earth.</p>
<p>The idea that God drove the heavens is very old. Because people thought that their god (or gods) guided all heavenly occurrences, it’s not surprising that many people – <a href="http://idp.bl.uk/4DCGI/education/astronomy/sky.html">ancient Chinese</a>, for example, and <a href="http://www.ibtimes.co.uk/solar-eclipse-apocalypse-how-ancient-civilisations-explained-disappearance-sun-1492508">Egyptians and Europeans</a> – believed that what they witnessed in the skies above provided signs of future events. </p>
<p>For this reason, solar eclipses were for many centuries understood to be harbingers of good or evil for humankind. They were attributed <a href="https://www.timeanddate.com/eclipse/solar-eclipse-history.html">magical or mysterious predictive qualities</a> that could influence human lives. During the first century A.D., people – including astrologers, magicians, alchemists and mystics – who claimed to have mastery over supernatural phenomena held sway over kings, religious leaders and whole populations.</p>
<p>Nicholas Copernicus, whose life straddled the 15th and 16th centuries, used scientific methods to devise a more accurate understanding of the solar system. In his famous book, “On the Revolutions of the Celestial Spheres” (published in 1543), Copernicus showed that the planets revolved around the sun. He didn’t get it all right, though: He thought planetary bodies had circular orbits, because the Christian God would have designed perfect circles in the cosmos. That planetary motion is elliptical is a later discovery.</p>
<p>By the time Benjamin Franklin grew up in New England (about 150 years later), few people still believed in the Ptolemaic system. Most had learned from living in an increasingly enlightened culture that the Copernican system was more reliable. Franklin, like many in his generation, believed that knowledge about the scientific causes for changes in the environment could work to reduce human fears about what the skies might portend. </p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/181276/original/file-20170807-25576-1ftk19s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/181276/original/file-20170807-25576-1ftk19s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/181276/original/file-20170807-25576-1ftk19s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=861&fit=crop&dpr=1 600w, https://images.theconversation.com/files/181276/original/file-20170807-25576-1ftk19s.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=861&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/181276/original/file-20170807-25576-1ftk19s.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=861&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/181276/original/file-20170807-25576-1ftk19s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1081&fit=crop&dpr=1 754w, https://images.theconversation.com/files/181276/original/file-20170807-25576-1ftk19s.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1081&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/181276/original/file-20170807-25576-1ftk19s.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1081&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">By measuring the height of celestial objects with an astrolabe, a user could predict the position of stars, planets and the sun.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Astrolabe_planisférique.jpg">Pom²</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>It was an age of wonder, still, but wonder was harnessed to technological advances that could help people understand better the world they lived in. Accurate instruments, such as the astrolabe, allowed people to measure the motion of the planets and thus predict movements in the heavens, particularly phenomena like solar and lunar eclipses and the motions of planets like Venus.</p>
<p>In his earliest printed articles, Franklin criticized the idea that education belonged solely to the elite. He hoped to bring knowledge to common people, so they could rely on expertise outside of what they might hear in churches. Franklin opted to use his own almanacs – along with his satirical pen – to help readers distinguish between astronomical events and astrological predictions.</p>
<h2>Old-fashioned almanacs</h2>
<p>Printing was a major technological innovation during the 16th, 17th and 18th centuries that helped foster information-sharing, <a href="https://sites.google.com/a/umich.edu/from-tablet-to-tablet/final-projects/-almanacs-in-17th-and-18th-century-america-michael-myckowiak-14">particularly via almanacs</a>.</p>
<p>These amazing compilations included all kinds of useful information and were relied on by farmers, merchants, traders and general readers in much the same way we rely on smartphones today. Colonial American almanacs provided the estimated times of sunrises and sunsets, high and low tides, periods of the moon and sun, the rise and fall of constellations, solar and lunar eclipses, and the transit of planets in the night skies. More expensive almanacs included local information such as court dates, dates of markets and fairs, and roadway distances between places. Most almanacs also offered standard reference information, including lists of the reigns of monarchs of England and Europe, along with a chronology of important dates in the Christian Era. </p>
<p><a href="https://newenglandquarterly.wordpress.com/2013/08/27/colonial-almanacs/">Almanac culture dominated New England life</a> when Franklin was a youth. They were the most purchased items American printers offered, with many a printer making his chief livelihood by printing almanacs.</p>
<p>Almanacs were money-makers, so <a href="http://www.librarycompany.org/BFWriter/poor.htm">Franklin developed his own version</a> shortly after he opened his own shop in Philadelphia. The city already had almanac-makers – Titan Leeds and John Jerman, among others – but Franklin aimed to gain the major share of the almanac trade.</p>
<p>Franklin considered astrological prediction foolish, especially in light of new scientific discoveries being made about the universe. He thought almanacs should not prognosticate on future events, as if people were still living in the dark ages. So he found a way to <a href="http://www.vlib.us/amdocs/texts/prichard44.html">make fun of his competitors</a> who continued to pretend they could legitimately use eclipses, for instance, to predict future events.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/181278/original/file-20170807-28176-k1oa3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/181278/original/file-20170807-28176-k1oa3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/181278/original/file-20170807-28176-k1oa3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=469&fit=crop&dpr=1 600w, https://images.theconversation.com/files/181278/original/file-20170807-28176-k1oa3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=469&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/181278/original/file-20170807-28176-k1oa3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=469&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/181278/original/file-20170807-28176-k1oa3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=590&fit=crop&dpr=1 754w, https://images.theconversation.com/files/181278/original/file-20170807-28176-k1oa3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=590&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/181278/original/file-20170807-28176-k1oa3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=590&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Franklin dispensed many aphorisms in the guise of ‘Poor Richard,’ such as ‘Love your Enemies, for they tell you your Faults.’</span>
<span class="attribution"><a class="source" href="http://www.loc.gov/pictures/item/2003654338/">Oliver Pelton</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>Introducing Poor Richard</h2>
<p>In addition to the usual fare, <a href="http://www.benjamin-franklin-history.org/poor-richards-almanac/">Franklin’s almanac provided</a> stories, aphorisms and poems, all ostensibly curated by a homespun character he created: <a href="http://www.librarycompany.org/BFWriter/poor.htm">Richard Saunders, the fictional “author”</a> of Franklin’s “Poor Richard’s Almanac.”</p>
<p>The “Poor Richard” Saunders persona allowed Franklin to satirize almanac makers who still wrote about eclipses as occult phenomena. Satire works because it closely reproduces the object being made fun of, with a slight difference. We’re familiar with this method today from watching skits on “Saturday Night Live” and other parody programs.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/181280/original/file-20170807-20706-16xeqxh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/181280/original/file-20170807-20706-16xeqxh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/181280/original/file-20170807-20706-16xeqxh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=1094&fit=crop&dpr=1 600w, https://images.theconversation.com/files/181280/original/file-20170807-20706-16xeqxh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=1094&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/181280/original/file-20170807-20706-16xeqxh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=1094&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/181280/original/file-20170807-20706-16xeqxh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1375&fit=crop&dpr=1 754w, https://images.theconversation.com/files/181280/original/file-20170807-20706-16xeqxh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1375&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/181280/original/file-20170807-20706-16xeqxh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1375&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Title page of Franklin’s first ‘Poor Richard’ almanac, for 1733.</span>
</figcaption>
</figure>
<p>Franklin’s voice was close enough to his satirical target that “Poor Richard” stole the market. For instance, Poor Richard began his career by predicting the death of Titan Leeds, his competitor. He later would do the same thing to John Jerman. Franklin was determined to mock almanac-makers who pretended to possess occult knowledge. Nobody knows when a person might die, and only astrologers would pretend to think a solar or lunar eclipse might mean something for humans.</p>
<p>Franklin included a wonderfully funny section in his almanac for 1735, making light of his competitors who did offer astrological prognostications. As “Poor Richard,” he wrote:</p>
<blockquote>
<p>“I shall not say much of the Signification of the Eclipses this Year, for in truth they do not signifie much; only I may observe by the way, that the first Eclipse of the Moon being celebrated in Libra or the Ballance, foreshews a Failure of Justice, where People judge in their own Cases. But in the following Year 1736, there will be six Eclipses, four of the Sun, and two of the Moon, which two Eclipses of the Moon will be both total, and portend great Revolutions in Europe, particularly in Germany….”</p>
</blockquote>
<p>Richard Saunders is clear in the opening remark that “Eclipses … do not signifie much.” He nonetheless goes on to base amazing predictions for 1736 on them, in effect lampooning anyone who would rely on the stars to foretell human events. Great revolutions were taking place in Europe, but no one needed to read eclipses in order to figure that out; they needed only to read the day’s newspapers.</p>
<p>The next year, Franklin decided go a step further than just satirizing these occult prognostications. He had Richard Saunders explain his understanding of some of the science behind eclipses. He characterized the “Difference between Eclipses of the Moon and of the Sun” by reporting that:</p>
<blockquote>
<p>“All Lunar Eclipses are universal, i.e. visible in all Parts of the Globe which have the Moon above their Horizon, and are every where of the same Magnitude: But Eclipses of the Sun do not appear the same in all Parts of the Earth where they are seen; being when total in some Places, only partial in others; and in other Places not seen at all, tho’ neither Clouds nor Horizon prevent the Sight of the Sun it self.”</p>
</blockquote>
<p>The goal of an explanation like this? To eclipse occult belief. He hoped people would become more confident about the universe and everything in it and would learn to rely on <a href="http://nationaleclipse.com/history.html">scientifically validated knowledge</a> rather than an almanac-maker’s fictions.</p><img src="https://counter.theconversation.com/content/80309/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Carla J. Mulford 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>Franklin advanced a scientific – not supernatural – understanding of astronomical events such as eclipses. His satirical character ‘Poor Richard’ mocked those who bought into astrological predictions.Carla J. Mulford, Professor of English, Penn StateLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/812482017-08-08T21:10:26Z2017-08-08T21:10:26ZHow eclipses were regarded as omens in the ancient world<figure><img src="https://images.theconversation.com/files/181225/original/file-20170807-25556-1lixvch.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A solar eclipse observed over Grand Canyon National Park in May 2012.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/grand_canyon_nps/7245482574/in/photolist-c3fZxm-c3fXdW-c3fWx7-c3epum-c3eqTy-c3fY4y-57163S-c3epM9-c3fYVE-c3fXwy-C5XxB-c3g3CG-c3eqhY-fCVGm6-c3fZSh-fDdfNN-6F5DmM-c3g1tA-c3eoRU-c3fZdY-fPPjmU-aYNkx6-c3g3XC-aYNupX-aAEsP-pejVdz-c3g1a7-c3g2Fm-c3er2b-iKxDU4-c3g1RQ-c3g3iu-fF8ZAi-VXgGtY-zaEMKZ-z8mWNC-z8mWQb-7qMunB-ym8ku1-VXgSNA-VL4BXE-yT9Zdt-zaEPmV-VRwoZc-UJqhU9-UJqnCC-VqBEXm-VXgL2Q-VXgLD1-UJtxeq">Grand Canyon National Park </a></span></figcaption></figure><p>On <a href="https://science.nasa.gov/eclipses/future-eclipses/eclipse-2024/">April 8</a>, millions of Americans will be able to see the magic of a total solar eclipse.</p>
<p>Humans have been alternatively <a href="https://books.google.com/books?id=t_hnvgAACAAJ&printsec=frontcover#v=onepage&q=strange%20behavior&f=false">amused, puzzled, bewildered and sometimes even terrified</a> at the sight of this celestial phenomenon. A range of social and cultural reactions <a href="https://global.oup.com/academic/product/totality-the-great-american-eclipses-of-2017-and-2024-9780198795698?cc=us&lang=en&">accompanies the observation of an eclipse</a>. In ancient Mesopotamia (roughly modern Iraq), eclipses were in fact regarded as omens, as signs of things to come. </p>
<h2>Solar and lunar eclipses</h2>
<p>For an eclipse to take place, three celestial bodies must find themselves in a straight line within their elliptic orbits. This is called a syzygy, from the Greek word “súzugos,” meaning yoked or paired. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/181229/original/file-20170807-25556-99aycz.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/181229/original/file-20170807-25556-99aycz.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=299&fit=crop&dpr=1 600w, https://images.theconversation.com/files/181229/original/file-20170807-25556-99aycz.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=299&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/181229/original/file-20170807-25556-99aycz.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=299&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/181229/original/file-20170807-25556-99aycz.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=376&fit=crop&dpr=1 754w, https://images.theconversation.com/files/181229/original/file-20170807-25556-99aycz.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=376&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/181229/original/file-20170807-25556-99aycz.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=376&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Solar lunar eclipse diagram.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File%3ASolar_lunar_eclipse_diagram.png">Tomruen (Own work) via Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>From our viewpoint on Earth, there are two kinds of eclipses: solar and lunar. In a solar eclipse, the moon passes in between the sun and Earth, which results in blocking our view of the sun. In a lunar eclipse, it is the moon that crosses through the shadow of the Earth. A solar eclipse can completely block our view of the sun, but it is usually a brief event and can be observed only in certain areas of the Earth’s surface; what can be viewed as a total eclipse in one’s hometown may just be a partial eclipse a few hundred miles away.</p>
<p>By contrast, a lunar eclipse can be viewed throughout an entire hemisphere of the Earth: the half of the surface of the planet that happens to be on the night side at the time. </p>
<h2>Eclipses as omens</h2>
<p>More than two thousand years ago, the <a href="https://books.google.com/books?id=TjiVXdSMRu4C&printsec=frontcover&dq=the+heavenly+writing&hl=en&sa=X&ved=0ahUKEwj3laXx06TVAhUBWz4KHb2yBQwQ6AEIJjAA#v=onepage&q=223%20months&f=false">Babylonians</a> were able to <a href="https://books.google.com/books?id=7hnTZ8tdOS0C&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q=223%20months&f=false">calculate</a> that there were 38 possible eclipses or syzygys within a period of 223 months: that is, about 18 years. This period of 223 months is called a <a href="https://eclipse.gsfc.nasa.gov/SEsaros/SEsaros.html">Saros cycle</a> by modern astronomers, and a sequence of eclipses separated by a Saros cycle constitutes a Saros series. </p>
<p>Although scientists now know that the number of <a href="https://eclipse.gsfc.nasa.gov/LEsaros/LEperiodicity.html#section103">lunar</a> and <a href="http://www.solar-eclipse.de/en/saros/active/">solar</a> eclipses is not exactly the same in every Saros series, one cannot underplay the achievement of Babylonian scholars in understanding this astronomical phenomenon. Their realization of this <a href="https://books.google.com/books?id=ih8LAAAAIAAJ&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false">cycle</a> eventually allowed them to <a href="http://www.oocities.org/hazarry/astronomy/eclipse_predction.pdf">predict</a> the occurrence of an eclipse. </p>
<p>The level of astronomical knowledge achieved in ancient Babylonia (southern Mesopotamia) cannot be separated from the astrological tradition that regarded eclipses as omens: Astronomy and astrology were then two sides of the same coin. </p>
<h2>Rituals to preempt royal fate</h2>
<p>According to Babylonian scholars, eclipses could foretell the death of the king. The conditions for an omen to be considered as such were not simple. For instance, according to a famous astronomical work known by its initial words, <a href="https://books.google.com/books?id=JimYncnzaOkC&printsec=frontcover&dq=letters+from+assyrian+scholars+parpola&hl=en&sa=X&ved=0ahUKEwi_6quU2KTVAhWG4D4KHa3EBz0Q6AEILTAB#v=onepage&q=substitute%20king&f=false">“Enūma Anu Enlil”</a> – “When (the gods) Anu and Enlil” – if Jupiter was visible during the eclipse, the king was safe. Lunar eclipses seem to have been of particular concern for the well-being and <a href="https://books.google.com/books?id=TjiVXdSMRu4C&printsec=frontcover&dq=the+heavenly+writing&hl=en&sa=X&ved=0ahUKEwj3laXx06TVAhUBWz4KHb2yBQwQ6AEIJjAA#v=onepage&q=substitute%20king&f=false">survival of the king</a>.</p>
<p>In order to preempt the monarch’s fate, a mechanism was devised: the “<a href="https://books.google.com/books?id=JimYncnzaOkC&printsec=frontcover&dq=letters+from+assyrian+scholars+parpola&hl=en&sa=X&ved=0ahUKEwi_6quU2KTVAhWG4D4KHa3EBz0Q6AEILTAB#v=onepage&q=substitute%20king&f=false">substitute king ritual</a>,” or “šar pūhi.” There are over 30 mentions of this ritual in various letters from <a href="http://www.wiley.com/WileyCDA/WileyTitle/productCd-111871816X.html">Assyria</a> (northern Mesopotamia), dating to the first millennium B.C. Earlier references to a similar <a href="https://books.google.com/books?id=_4NSAwAAQBAJ&pg=PA208&dq=hittites+%22substitute+king%22&hl=en&sa=X&ved=0ahUKEwjE3JH5zrHVAhWJez4KHb9LB8MQ6AEIKzAB#v=onepage&q=hittites%20%22substitute%20king%22&f=false">ritual</a> have also been found in <a href="https://secure.aidcvt.com/sbl/ProdDetails.asp?ID=061707P">texts in Hittite</a>, the Indo-European language for which we have the earliest written records, dating to second-millennium Anatolia – modern-day Turkey. </p>
<h2>Saving the king</h2>
<p><a href="https://books.google.com/books?id=JimYncnzaOkC&printsec=frontcover&dq=letters+from+assyrian+scholars+parpola&hl=en&sa=X&ved=0ahUKEwi_6quU2KTVAhWG4D4KHa3EBz0Q6AEILTAB#v=onepage&q=substitute%20king&f=false">In this ritual</a>, a person would be chosen to replace the king. He would be dressed like the king and placed on the throne. To avoid confusion with a real coronation, all this would occur alongside the recitation of the negative omen triggered by the observation of the eclipse.</p>
<p>The real king would keep a low profile and avoid being seen. If no additional negative portents were observed, the substitute king was put to death, therefore fulfilling the prophetic reading of the celestial omen while saving the life of the real king. This ritual would take place when an eclipse was observed or even <a href="https://books.google.com/books?id=JimYncnzaOkC&pg=PA177&lpg=PA177&dq=%22substitute+king%22+eclipse+predict&source=bl&ots=bgfVsOicV4&sig=YoNxzkQjXjw1wRun_hQkPGkPpFo&hl=en&sa=X&ved=0ahUKEwjHl7z25rHVAhWD1CYKHQJiBngQ6AEIKzAB#v=onepage&q=%22substitute%20king%22%20eclipse%20predict&f=false">predicted</a>, something that became possible to do in <a href="https://books.google.com/books?id=7hnTZ8tdOS0C&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q=predict&f=false">later periods</a>. </p>
<p>The presence of this ritual among the corpus of Hittite texts in second-millennium Anatolia has led to the assumption that it must have existed already in Mesopotamia during the first half of the second millennium B.C. </p>
<h2>A legend</h2>
<p>Although omens predicting the death of the king are already known for this earlier
period, the truth is that the main basis for such an assumption is an interesting story preserved only in a much later, first-millennium composition known by modern scholars as the <a href="http://www.livius.org/sources/content/mesopotamian-chronicles-content/abc-20-chronicle-of-early-kings/">“Chronicle of Early Kings</a>.” </p>
<p>According to this <a href="https://books.google.com/books?id=NGwYAgAAQBAJ&pg=PA334&lpg=PA334&dq=%22erra-imitti%22+%22enlil-bani%22+chronicle+isin&source=bl&ots=tPoVh86MF_&sig=dG7kHKpKYQlXB5N1fkUG3dQPdxw&hl=en&sa=X&ved=0ahUKEwir7MHX4qTVAhWDNT4KHafzAwYQ6AEINDAD#v=onepage&q=%22erra-imitti%22%20%22enlil-bani%22%20chronicle%20isin&f=false">late chronicle</a>, a king of the city of Isin (modern Išān Bahrīyāt, about 125 miles to the southeast of Baghdad), Erra-imitti, was replaced by a gardener called Enlil-bani as part of a substitute king ritual. Luckily for this gardener, the real king died while eating hot soup, so the gardener remained on the throne and became king for good. </p>
<p>The fact is that these two kings, Erra-imitti and Enlil-bani, did exist and reigned successively in Isin during the 19th century B.C. The story, however, as told in the late “Chronicle of Early Kings,” bears all the trademarks of a legend. The story was probably devised to explain a dynastic switch, in which the royal office passed from one family or lineage to another, instead of following the usual father-son line of succession.</p>
<h2>Looking for meaning in the skies</h2>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/181236/original/file-20170807-25500-1euuy6f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/181236/original/file-20170807-25500-1euuy6f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/181236/original/file-20170807-25500-1euuy6f.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/181236/original/file-20170807-25500-1euuy6f.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/181236/original/file-20170807-25500-1euuy6f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/181236/original/file-20170807-25500-1euuy6f.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/181236/original/file-20170807-25500-1euuy6f.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">
<figcaption>
<span class="caption">A lunar eclipse.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/nsaunders/15298803219/in/photolist-piUnci-Caqqo-9TRc5w-4tvD3z-9TMW7i-CbjUN-4uXRdv-4vnQYS-93Km6N-cbAJLo-4tvsvc-9YzeKV-4tzkmj-4tMwJD-5dDoQa-4tRumf-4w4Zxp-9Zz58F-9rFvro-4tzjvW-dDmiBU-pApZyi-9rCxh2-D6bJg-5esUbp-4tv5na-5esUgn-4tyS1j-4tv6zD-4viMF8-2V6TTC-9TVYRJ-2VX6qr-4tz8eL-2VaKBf-CbjGD-2V8xKY-pifSiD-5dPPWw-4tvdgR-nbXQeb-baDGZx-9rFvRN-2VQVBd-9G9PX5-Cecor-baDGWV-n8q5e6-baDH2n-93yiu1">Neil Saunders</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<p>Mesopotamia was not unique in this regard. For instance, a chronicle of early China known as the “Bamboo Annals” (竹書紀年 Zhúshū Jìnián) refers to a total lunar eclipse that took place in <a href="https://books.google.com/books?id=wUuyAAAAQBAJ&printsec=frontcover&dq=pankenier+astrology+china&hl=en&sa=X&ved=0ahUKEwiDzqWU6KTVAhUTID4KHb4EB2gQ6AEIJjAA#v=onepage&q=1059&f=false">1059 B.C.</a>, during the reign of the last king of the Shang dynasty. This eclipse was regarded as a sign by a vassal king, Wen of the Zhou dynasty, to challenge his Shang overlord.</p>
<p>In the later <a href="https://books.google.com/books?id=wUuyAAAAQBAJ&printsec=frontcover&dq=pankenier+astrology+china&hl=en&sa=X&ved=0ahUKEwiDzqWU6KTVAhUTID4KHb4EB2gQ6AEIJjAA#v=onepage&q=1059&f=false">account</a> contained in the “Bamboo Annals,” an eclipse would have triggered the political and military events that marked the transition from the Shang to the Zhou dynasty in ancient China. As in the case of the Babylonian “Chronicle of Early Kings,” the “Bamboo Annals” are a history of earlier periods compiled at a later time. The “<a href="https://books.google.com/books?id=2JNV_j-q64IC&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q=the%20editing%20and%20editions&f=false">Bamboo Annals</a>” were allegedly found in a tomb about A.D. 280, but they purport to date to the reign of the King Xiang of Wei, who died in 296 B.C.</p>
<p>The complexity of human events is rarely constrained and determined by one single factor. Nevertheless, whether in ancient Mesopotamia or in early China, eclipses and other omens provided contemporary justifications, or after-the-fact explanations, for an entangled set of variables that decided a specific course of history. </p>
<p>Even if they mix astronomy and astrology, or history with legend, humans have been preoccupied with the inescapable anomaly embodied by an eclipse for as long as they have looked at the sky.</p><img src="https://counter.theconversation.com/content/81248/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Gonzalo Rubio 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>More than 2,000 years ago, the Babylonians understood the cycle of eclipses. They also regarded them as signs that could foretell the death of a king.Gonzalo Rubio, Associate Professor of Classics & Ancient Mediterranean Studies, History, and Asian Studies, Penn StateLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/806362017-08-08T00:57:14Z2017-08-08T00:57:14ZScientist at work: Why this meteorologist is eager for an eclipse<figure><img src="https://images.theconversation.com/files/181075/original/file-20170804-27483-1h1khg2.jpg?ixlib=rb-1.1.0&rect=209%2C0%2C1622%2C1072&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Hiscox and students practice for the big day with a weather balloon.</span> <span class="attribution"><span class="source">Joshua Burrack</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p>By all accounts a total solar eclipse is a life-changing event. I wouldn’t know, I’ve never seen one. Fortunately for me and millions across the U.S., that will change this summer.</p>
<p>I’m not really an eclipse expert, even though I can’t wait for August 21. I’m actually a meteorologist, and a fairly specialized one at that. Six months ago, I didn’t know the difference between an umbra and penumbra. What I did know is that the sun provides energy for everything that happens on our planet, and that the daily cycle of sun rising and setting is a key component of what happens in the atmosphere, and how air circulates locally and globally. </p>
<p>So why is someone who worries about subsecond- and submeter-scale winds interested in this astronomical-scale event? Because any change in incoming sun – such as the complete blackout during a total solar eclipse – will affect the energy received by the land, and in turn the energy transferred back to the atmosphere. And because the total eclipse period is short, those changes will be small. It’s both an exciting event and an interesting challenge: a scientist’s dream.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/181116/original/file-20170806-10088-1o0whzd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/181116/original/file-20170806-10088-1o0whzd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/181116/original/file-20170806-10088-1o0whzd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=408&fit=crop&dpr=1 600w, https://images.theconversation.com/files/181116/original/file-20170806-10088-1o0whzd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=408&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/181116/original/file-20170806-10088-1o0whzd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=408&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/181116/original/file-20170806-10088-1o0whzd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=513&fit=crop&dpr=1 754w, https://images.theconversation.com/files/181116/original/file-20170806-10088-1o0whzd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=513&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/181116/original/file-20170806-10088-1o0whzd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=513&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 mini-night caused by the moon blacking out the sun during the day is an opportunity to investigate many scientific questions.</span>
<span class="attribution"><a class="source" href="http://www.apimages.com/metadata/Index/Russia-Europe-Solar-Eclipse/44d1094c93774d39a3324d19adb5efee/1/0">AP Photo/Dmitry Lovetsky</a></span>
</figcaption>
</figure>
<p>Coupled with advances in observational techniques, every eclipse offers a new chance to prove meteorological theories. This one even more so because coordination across the entire length of the continental United States almost guarantees that someone will have ideal observing conditions. We’re prepping our weather balloons and weather stations to take advantage of that opportunity – to see exactly what a short blackout does to atmospheric motion.</p>
<h2>Meteorology all goes back to the sun</h2>
<p>From how <a href="https://www.epa.gov/ozone-pollution">pollutants are formed and transported</a>, to how plants exchange carbon using photosynthesis, to what direction the wind blows, daytime processes are <a href="https://doi.org/10.1175/JAS3654.1">different from nighttime processes</a>. Without energy input from the sun, the lower atmosphere slowly flips itself at night. </p>
<p>During the day, it’s warm near the ground and cooler up above; at night it’s just the opposite. This “stable” (warmer over cooler) air inhibits vertical motion of the air and anything suspended in it. So <a href="https://doi.org/10.1191/0309133305pp442ra">pollutants can stay closer to the ground</a>, <a href="https://doi.org/10.1175/1520-0469(2001)058%3C1409:FADONB%3E2.0.CO;2">clouds form differently</a>, <a href="https://doi.org/10.1175/1520-0469(1967)024%3C0029:KWITEA%3E2.0.CO;2">air flows faster down valleys</a> and at the coasts <a href="http://www.srh.noaa.gov/jetstream/ocean/seabreeze.html">wind blows offshore instead of on</a>. </p>
<p>While those generalities are known, the nuances and timings aren’t fully understood, and thus they are not completely predictable. That’s my sphere of science – turbulence. I’m interested in the atmospheric changes in short times and small spaces that can eventually influence the larger “weather” most people are familiar with.</p>
<p>The total solar eclipse is a mini-night experience, so we will use it as a natural experiment. Is a brief period without solar radiation enough to cause detectable changes in turbulence and stability, or is it the slower interactions of land and atmosphere over a whole night that are required? We’ll take what we find and use it to think about normal non-eclipse conditions.</p>
<h2>Head in the sky</h2>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/181066/original/file-20170804-6948-1y2u1lq.gif?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/181066/original/file-20170804-6948-1y2u1lq.gif?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/181066/original/file-20170804-6948-1y2u1lq.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=329&fit=crop&dpr=1 600w, https://images.theconversation.com/files/181066/original/file-20170804-6948-1y2u1lq.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=329&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/181066/original/file-20170804-6948-1y2u1lq.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=329&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/181066/original/file-20170804-6948-1y2u1lq.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=413&fit=crop&dpr=1 754w, https://images.theconversation.com/files/181066/original/file-20170804-6948-1y2u1lq.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=413&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/181066/original/file-20170804-6948-1y2u1lq.gif?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=413&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 troposphere is the part of the atmosphere closest to Earth’s surface and includes the air we breathe.</span>
<span class="attribution"><a class="source" href="https://www.giss.nasa.gov/research/features/201210_shindell/">NASA ESPO/INTEX-NA Educational Outreach</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>By launching a series of weather balloons before, during and after the eclipse we will see the evolution of winds and temperatures above the Earth’s surface over time. The instrument packages attached to the balloons take measurements from about 100 meters above the surface up through the lower atmosphere, troposphere and lower stratosphere, eventually reaching nearly 20 kilometers. Scientists are coordinating all across the eclipse’s path, and will conduct this same experiment at <a href="http://eclipse.montana.edu/">several sites</a> across the country.</p>
<p>At our site in South Carolina, we are focusing on the question of whether a total eclipse can generate internal atmospheric <a href="http://glossary.ametsoc.org/wiki/Gravity_wave">gravity waves</a>: parcels of air moving together as chunks trying to regain an equilibrium in temperature and density. (These are different from the <a href="https://theconversation.com/gravitational-waves-discovered-top-scientists-respond-53956">gravitational waves</a> that result when black holes collide.) Sometimes gravity waves are visible in clouds. During previous eclipses <a href="https://doi.org/10.1098/rsta.2015.0222">there has been promising evidence</a> of gravity wave activity, but not enough data from enough locations to fully understand them.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/181044/original/file-20170804-10658-igira4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/181044/original/file-20170804-10658-igira4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/181044/original/file-20170804-10658-igira4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=462&fit=crop&dpr=1 600w, https://images.theconversation.com/files/181044/original/file-20170804-10658-igira4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=462&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/181044/original/file-20170804-10658-igira4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=462&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/181044/original/file-20170804-10658-igira4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=580&fit=crop&dpr=1 754w, https://images.theconversation.com/files/181044/original/file-20170804-10658-igira4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=580&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/181044/original/file-20170804-10658-igira4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=580&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 pattern of atmospheric gravity waves is visible in this satellite image of double, overlapping arcs of clouds over the Indian Ocean.</span>
<span class="attribution"><a class="source" href="https://visibleearth.nasa.gov/view.php?id=69463">Jacques Descloitres, MODIS Rapid Response Team, NASA/GSFC</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>The vertical profiles of temperature, relative humidity, wind speed and wind direction we collect will be used to answer a number of other scientific questions as well. First, we’ll add to the sparse database of eclipse-induced temperature changes and provide quantitative measures of how strong the temperature change is and how long the lag between the total blackness at solar minimum and the temperature minimum is.</p>
<p>We will also be able to see if the cooling when the sun disappears and sudden rewarming when it returns propagates vertically and, if so, how far above the Earth’s surface it goes. In terms of wind, questions to be answered center around changes in wind speed and turbulence intensity. We believe we will see a reduction of both, which provides further explanation for the eerie “<a href="https://phys.org/news/2016-08-mystery-eclipse-years.html">eclipse wind</a>” so often cited by human observers.</p>
<p>This more comprehensive examination of the troposphere and stratosphere in time and space will help inform our modeling and prediction of regional weather and climate.</p>
<h2>Feet on the ground</h2>
<p>But what if the changes are smaller? A helium-filled balloon leaves the ground quickly – ideally at five meters per second – and the first reliable measurement is almost 100 meters above the ground. A lot can happen in 100 meters.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/181067/original/file-20170804-2386-s32kso.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/181067/original/file-20170804-2386-s32kso.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/181067/original/file-20170804-2386-s32kso.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/181067/original/file-20170804-2386-s32kso.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/181067/original/file-20170804-2386-s32kso.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/181067/original/file-20170804-2386-s32kso.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/181067/original/file-20170804-2386-s32kso.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/181067/original/file-20170804-2386-s32kso.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">Postdoc Alexandria McCombs and graduate students Mayra Roman-Rivera and Peter Tereskiewicz work on installing meteorological instruments in preparation for the eclipse experiment.</span>
<span class="attribution"><span class="source">Ian Giammanco, Insurance Institute for Business & Home Safety,DisasterSafety.org</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>To fill in that gap, at our site in South Carolina, we are adding other measurements. We’ve erected a small tower with fine thermocouples every half-meter from the ground up. These thin wires can detect temperature changes over 0.1-second time periods and will help us see if the darkness causes a very shallow layer of cooler air to start to grow under the typical daytime warmth. </p>
<p>The tower will also house two sonic anemometers – sensors that use disruption in a sound pulse to measure the wind speed in three dimensions at very fast rates – to see if a <a href="http://glossary.ametsoc.org/wiki/Wind_shear">wind shear</a> develops near ground level.</p>
<p>An infrared gas analyzer will record carbon fluxes throughout the eclipse period to see if there is any detectable change in plant respiration. Remember, they “breathe” in carbon dioxide. <a href="http://sciencing.com/animals-reaction-solar-eclipse-3503.html">Some animals interpret an eclipse as night</a> – do the plants?</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/181069/original/file-20170804-2386-e2v3uh.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/181069/original/file-20170804-2386-e2v3uh.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/181069/original/file-20170804-2386-e2v3uh.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/181069/original/file-20170804-2386-e2v3uh.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/181069/original/file-20170804-2386-e2v3uh.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/181069/original/file-20170804-2386-e2v3uh.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/181069/original/file-20170804-2386-e2v3uh.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/181069/original/file-20170804-2386-e2v3uh.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 USC backscatter lidar at a recent field deployment in New Zealand.</span>
<span class="attribution"><span class="source">April Hiscox</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Finally, we’ll also deploy a lidar system. That’s like a radar, but with a laser that will point upward. This is to see if there are any changes in the depth of the boundary layer – a transition point between where the atmosphere is affected by the Earth’s surface to the free troposphere above.</p>
<p>And we’re going to do all of this in just two minutes and 36 seconds. A tiny window for a big impact.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/181070/original/file-20170804-7490-3b1kae.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/181070/original/file-20170804-7490-3b1kae.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/181070/original/file-20170804-7490-3b1kae.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/181070/original/file-20170804-7490-3b1kae.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/181070/original/file-20170804-7490-3b1kae.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/181070/original/file-20170804-7490-3b1kae.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/181070/original/file-20170804-7490-3b1kae.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/181070/original/file-20170804-7490-3b1kae.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">A practice weather balloon soars above the USC campus.</span>
<span class="attribution"><span class="source">Patrick Remson</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>Collating the data to flesh out the theory</h2>
<p>A total solar eclipse is often referred to as a meteorological playground, and that is just how it feels. We’re taking out all our scientific toys to see what we can find. Eclipse events are relatively rare; meteorologists like me take what we know about the interactions between land and air to think logically about what will happen during an eclipse. But until we see it, put an equation on it and predict the next one, it still falls into the realm of theory, not reliably predictable weather. </p>
<p>I feel like a kid again – the eclipse has forced me to think about meteorology in a new and different way – just like looking at the world while hanging upside down from monkey bars.</p><img src="https://counter.theconversation.com/content/80636/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>April Hiscox receives funding for eclipse related research from South Carolina Space Grant and The University of South Carolina Office of Research. </span></em></p>Meteorology researchers across the country are prepping experiments for the mini-night the eclipse will bring on August 21 – two minutes and 36 seconds without the sun in the middle of the day.April Hiscox, Associate Professor of Geography, University of South CarolinaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/813082017-08-03T21:10:14Z2017-08-03T21:10:14ZWhat would a solar eclipse look like from the Moon? An astronomer answers that and other total eclipse questions<figure><img src="https://images.theconversation.com/files/581028/original/file-20240311-16-32xcxy.jpg?ixlib=rb-1.1.0&rect=4065%2C19%2C4640%2C1457&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Composite image of moments before, during and after totality.</span> <span class="attribution"><a class="source" href="https://images.nasa.gov/details/NHQ201708210116">NASA/Aubrey Gemignani</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p><em>A total solar eclipse will be visible across the U.S. on Monday, April 8, 2024. Shannon Schmoll, director of the Abrams Planetarium at Michigan State University, explains why and how eclipses happen and what scientists can learn from an eclipse.</em></p>
<h2>1. How do astronomers know in advance when an eclipse is going to happen and where it will be visible?</h2>
<p>Solar eclipses happen when our view of the Sun is blocked by the Moon. When the Moon lines up between the Sun and Earth, the Moon will cast a shadow onto our planet. This is what we on the ground observe as a solar eclipse.</p>
<p>We know <a href="https://eclipse.gsfc.nasa.gov/eclipse.html">when they’ll happen</a> because over centuries astronomers have <a href="https://science.nasa.gov/eclipses/faq/">measured very precisely the motions</a> of the Earth, Moon and Sun and how they change over time.</p>
<p>With that data about the Moon – and similar information about the <a href="https://theperihelioneffect.com/how-far-is-the-earth-from-the-sun/">Earth’s orbit around the Sun</a> – astronomers can make mathematical models of their movements in relation to each other. Using those equations, we can <a href="https://eclipse.gsfc.nasa.gov/JSEX/JSEX-index.html">calculate tables of data</a> that can <a href="https://eclipse.gsfc.nasa.gov/SEpubs/5MKSE.html">predict what we will see on Earth</a>, depending on location, during an eclipse as well as when they will happen and how long they last.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/581022/original/file-20240311-25-u11sz6.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Diagram of solar eclipse path on Earth, stretching from Pacific Ocean, to Mexico diagonally NE to Maine" src="https://images.theconversation.com/files/581022/original/file-20240311-25-u11sz6.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/581022/original/file-20240311-25-u11sz6.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=601&fit=crop&dpr=1 600w, https://images.theconversation.com/files/581022/original/file-20240311-25-u11sz6.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=601&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/581022/original/file-20240311-25-u11sz6.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=601&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/581022/original/file-20240311-25-u11sz6.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=755&fit=crop&dpr=1 754w, https://images.theconversation.com/files/581022/original/file-20240311-25-u11sz6.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=755&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/581022/original/file-20240311-25-u11sz6.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=755&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Dark blue path traces the path of the April 8 eclipse from west to east across North America.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:SE2024Apr08T.png">Eclipse Predictions by Fred Espenak, NASA's GSFC</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>After April 8, the next <a href="https://eclipse.gsfc.nasa.gov/SEpubs/5MCSE.html">solar eclipse</a> that will run from coast to coast in North America <a href="https://nationaleclipse.com/maps/map_08122045.html">will be in 2045</a>.</p>
<h2>2. How often do eclipses happen?</h2>
<p>A solar eclipse happens, on average, a couple times a year. The <a href="https://theconversation.com/explainer-what-is-a-solar-eclipse-33019">Moon passes between the Earth and Sun</a> every 29 days. We call that time the “<a href="https://starchild.gsfc.nasa.gov/docs/StarChild/questions/question3.html">new moon</a>” – when the Moon is not visible in Earth’s nighttime sky.</p>
<p>However, the Moon’s orbit and the Sun’s path in our sky don’t match up exactly, so at most of those new moon events, the Moon appears above or below the Sun.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/581024/original/file-20240311-28-60xtvg.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Curved lines denoting the orbits of the Sun and Moon as seen by someone on Earth" src="https://images.theconversation.com/files/581024/original/file-20240311-28-60xtvg.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/581024/original/file-20240311-28-60xtvg.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=353&fit=crop&dpr=1 600w, https://images.theconversation.com/files/581024/original/file-20240311-28-60xtvg.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=353&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/581024/original/file-20240311-28-60xtvg.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=353&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/581024/original/file-20240311-28-60xtvg.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=443&fit=crop&dpr=1 754w, https://images.theconversation.com/files/581024/original/file-20240311-28-60xtvg.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=443&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/581024/original/file-20240311-28-60xtvg.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=443&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 blue line shows the ecliptic, the path the Sun appears to take in our sky as viewed from Earth. The white line shows the Moon’s orbit. For eclipses to happen, both the Sun and the Moon need to be within the area marked with yellow brackets.</span>
<span class="attribution"><span class="source">Shannon Schmoll</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Twice a year, though, there is a period when the Moon and the Sun line up with Earth – astronomers call this an eclipse season. It lasts about 34 days, long enough for the moon to complete a full orbit, and then some, of the Earth.</p>
<p>During each eclipse season, there are at least two eclipses visible from some parts of the Earth. At the full moon, there will be a lunar eclipse, when the Moon passes directly behind the Earth, resulting in a darker, reddish-colored Moon. And at the new moon, there will be a solar eclipse, when the Sun is blocked by the Moon. </p>
<h2>3. What can be learned from eclipse events, or are they just oddities in nature?</h2>
<p>Scientists can definitely learn things from eclipses. The outermost layer of the Sun, known as the corona, is difficult to study because it’s less bright than the rest of the Sun – so it’s hard to see it amid the rest of the Sun’s brightness.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/179226/original/file-20170721-28515-1ep69w1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="black circle of the Moon outlined by white rays against a dark sky" src="https://images.theconversation.com/files/179226/original/file-20170721-28515-1ep69w1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/179226/original/file-20170721-28515-1ep69w1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=408&fit=crop&dpr=1 600w, https://images.theconversation.com/files/179226/original/file-20170721-28515-1ep69w1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=408&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/179226/original/file-20170721-28515-1ep69w1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=408&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/179226/original/file-20170721-28515-1ep69w1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=513&fit=crop&dpr=1 754w, https://images.theconversation.com/files/179226/original/file-20170721-28515-1ep69w1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=513&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/179226/original/file-20170721-28515-1ep69w1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=513&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">During an eclipse, the Sun’s corona becomes visible to observers on Earth.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/sites/default/files/thumbnails/image/white_light_corona.jpg">NASA</a></span>
</figcaption>
</figure>
<p>When the Moon blocks the Sun, the corona becomes visible – it’s the famous visual of the halo of light around the dark disk of the Moon. Currently astronomers study this by creating an artificial eclipse with a mask built into special instruments on telescopes called coronagraphs. This strategy is great, but it doesn’t allow the best pictures. Eclipses give scientists opportunities to get more data to <a href="https://science.nasa.gov/eclipses/future-eclipses/eclipse-2024/eclipse-2024-science/">study the corona in depth</a>.</p>
<p>Researchers can also learn about Earth itself. In an area affected by an eclipse, the darkening of the Sun leads to a <a href="https://sunearthday.nasa.gov/2006/faq.php">sudden drop in temperature</a>. <a href="https://science.nasa.gov/eclipses/future-eclipses/eclipse-2024/eclipse-2024-science/">NASA-funded studies</a> during this eclipse will look at the effects from the eclipse on our atmosphere as well as what happens on land. Previous studies observed animal behavior during an eclipse in 2001 and noted that <a href="https://academic.oup.com/astrogeo/article-pdf/42/4/4.4/436602/42-4-4.4.pdf">some animals went through their night routines</a> as the Sun disappeared, while others became nervous.</p>
<p>And scientists can learn about the whole universe. More than 100 years ago, an eclipse proved a prediction Albert Einstein had made about gravity. That success helped make him a household name. In his <a href="https://asd.gsfc.nasa.gov/blueshift/index.php/2015/11/25/100-years-of-general-relativity/">general theory of relativity</a>, Einstein had predicted that <a href="https://eclipse2017.nasa.gov/testing-general-relativity">gravity could bend the path of light</a>. The effect he predicted was very slight, so it would best be viewed as the light passed a very large celestial body as part of its travels across a very long distance of space.</p>
<p><a href="http://adsabs.harvard.edu//full/seri/ApJ../0101//0000133.000.html">Sir Arthur Eddington</a>, an astronomer who helped further the study of general relativity and whose work is a major piece of our modern understanding of stars and black holes, used the <a href="http://dx.doi.org/10.1098/rsta.1920.0009">darkness provided by a solar eclipse</a> to look at the position of the stars’ light during the day, when they passed the Sun. He then <a href="https://www.wired.com/2009/05/dayintech-0529/">compared those positions to their known positions at night</a>. He saw that <a href="https://sunearthday.nasa.gov/2006/events/einstein.php">the gravity of the Sun had bent the path</a> – exactly as, and in the precise amount, Einstein had predicted.</p>
<h2>4. How weird is it that the Moon can basically exactly block out the Sun?</h2>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/179234/original/file-20170721-28465-1bbd0kr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Orange orb of the Sun with a small black dot visible against it" src="https://images.theconversation.com/files/179234/original/file-20170721-28465-1bbd0kr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/179234/original/file-20170721-28465-1bbd0kr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/179234/original/file-20170721-28465-1bbd0kr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/179234/original/file-20170721-28465-1bbd0kr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/179234/original/file-20170721-28465-1bbd0kr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/179234/original/file-20170721-28465-1bbd0kr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/179234/original/file-20170721-28465-1bbd0kr.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">Venus appears as a small dot in the upper left as it passes between the Sun and Earth in 2012.</span>
<span class="attribution"><a class="source" href="https://earthobservatory.nasa.gov/IOTD/view.php?id=78196">NASA</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>It is very unusual that the Moon and the Sun just happen to be at <a href="http://www.astronomy.com/magazine/ask-astro/2000/10/why-is-the-moon-exactly-the-same-apparent-size-from-earth-as-the-sun-surely-this-cannot-be-just-coincidence-the-odds-against-such-a-perfect-match-are-enormous">the right distances and sizes</a> to <a href="https://starchild.gsfc.nasa.gov/docs/StarChild/questions/understand_size.html">appear to have the same size</a> in our sky. This allows the Moon to perfectly block the Sun’s disk, while also showing us the corona.</p>
<p>Venus and Mercury, for instance, can also pass in front of the Sun from our perspective. However, they appear as small specks moving across the Sun.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/581370/original/file-20240312-26-9p5r91.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="conceptual cartoon of solar eclipse with Moon in between Sun and Earth, blocking sunlight" src="https://images.theconversation.com/files/581370/original/file-20240312-26-9p5r91.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/581370/original/file-20240312-26-9p5r91.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=302&fit=crop&dpr=1 600w, https://images.theconversation.com/files/581370/original/file-20240312-26-9p5r91.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=302&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/581370/original/file-20240312-26-9p5r91.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=302&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/581370/original/file-20240312-26-9p5r91.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=379&fit=crop&dpr=1 754w, https://images.theconversation.com/files/581370/original/file-20240312-26-9p5r91.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=379&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/581370/original/file-20240312-26-9p5r91.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=379&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">If you were on the dark side of the Moon during a solar eclipse, you could watch the Moon’s shadow travel across the Earth.</span>
<span class="attribution"><span class="source">Shannon Schmoll</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>5. What would someone standing on the Moon see happen on Earth? Would Earth get dark?</h2>
<p>If you were on the Moon, you would be able to see the effects of the solar eclipse on Earth only if you were standing on the Moon’s night side, the side facing the Earth. You would see a round shadow cast onto the Earth.</p>
<p>This particular eclipse’s shadow will first hit the Pacific Ocean, make landfall in Mazatlán, then move through Texas in a diagonal path toward Maine, ending off the coast of Newfoundland in the Atlantic Ocean. This path the shadow takes is called the path of totality. </p>
<p><iframe id="fmogF" class="tc-infographic-datawrapper" src="https://datawrapper.dwcdn.net/fmogF/3/" height="400px" width="100%" style="border: none" frameborder="0"></iframe></p>
<p><em>This is an updated version of an article originally published on Aug. 3, 2017.</em></p><img src="https://counter.theconversation.com/content/81308/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Shannon Schmoll 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>An astronomer explains how. why and when eclipses happen, what scientists can learn from them, and what they would look like if you were standing on the Moon.Shannon Schmoll, Director of the Abrams Planetarium, Michigan State UniversityLicensed as Creative Commons – attribution, no derivatives.