Frank Close - Eclipses: What Everyone Needs to KnowR

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On August 21, 2017, millions of people across the United States witnessed the Great American Eclipse of the Sun. I was one of them. The moment it was over, I was inundated with questions: What caused the weird shadows and colors in the build-up to totality? Were those ephemeral bands of shadows gliding across the ground in the seconds before totality real or an optical illusion? Why this, whats that, but above all, where and when can I see a total solar eclipse again?

If you want to experience this exquisite phenomenon in the United States, then keep your diary free on Monday April 8, 2024. However, if like me you cant wait that long, there are on average a couple of total solar eclipses every three years, but you might have to travel: in 2019 and 2020 to South America or the Pacific; in 2021 to Antarctica. You get a year off in 2022, but in 2023 you could go to Western Australia. And then, having become an umbraphilea lover of the Moons shadowyou can plan exciting trips into the future to witness this most beautiful of natural phenomena.

Whether you want to understand more about what you sawor missedin 2017, prepare for the next one, or just learn more about eclipses in myth, history, literature, art, and science, here, in this book, are my 101 things you need to know.

Frank Close, Oxford, England 2019

@closefrank

My thanks to all of you who suggested questions about eclipses; I hope the answers both satisfy those and raise new ones. For specific help, suggestions, and material I am indebted to Michael Berry, Ian Blatchford, Pedro Ferreira, Frances and Michael Green, Colin Humphreys, Andrew Kirk, Bill Kramer, Chris Lintott, Jay Pasachoff, Brian Stewart, Barnaby Taylor, and Toshio Turoki. At Oxford University Press in New York: Jeremy Lewis for suggesting this book and Sean Pidgeon for help in developing the concept; and in Oxford: Sonke Adlung and Harriet Konishi for help with diagrams and images, Brid Nowlam for copy editing, and Raj Suthan for overseeing the production.

Thanks also to those I have met at far-flung places while chasing solar eclipses for the education and inspiration you provided. I hope to be able to thank you in person under the shadow of the Moon someday.

The Moons diameter is 400 times smaller than the Suns, but the Moon is also 400 times closer to us, so, remarkably, the two bodies appear exactly the same size when viewed from the Earth. For about 14 days a month, the orbiting Moon is on the dayside of the spinning Earth, and the Suns light casts a shadow, which, most of the time, is projected far off into space. But, on very particular occasions, it falls onto Earththen, the Moon obscures our view of the Sun.

Figure 1.1 Total and Partial Solar Eclipses.

In the Moons umbra the Sun is totally eclipsed. The much larger region of penumbra is where the Sun is partly visible and partly eclipsed.

For a solar eclipse to happen, it must be daytime. A lunar eclipse, by contrast, occurs at night during the 14 days of the lunar month when the Moon is on the dark side of Earth, and visible at night. Moonshine is reflected sunlight. On the night of the full Moon, the Moon rises at sunset and sets at the end of the night as the Sun rises again. On one occasion during this period, when the Moon is directly opposite the Sun, it reflects sunlight directly: this is the literal full Moon. When this happens, Earths shadow is projected into space and may fall upon the Moon covering it either partially or totally. Then, instead of a bright full Moon, the Moon is eclipsed. It isnt invisible at totality, however, because Earths atmosphere bends some of the sunlight back toward the distant Moon and gives it a glowing orange outer region. This blood red Moon has inspired poets and mystics throughout the ages. A lunar eclipse on April 3, 33, the evening after the crucifixion of Jesus of Nazareth, was regarded as hugely significant by his followers. Both lunar and solar eclipses have inspired awe throughout history, and continue to do so even today.

Figure 1.2 Solar and Lunar Eclipses.

If the Moons umbra touches the surface of Earth, a total solar eclipse occurs over a small region, T. Earths shadow is much larger and if the Moon enters it a total lunar eclipse occurs, L.

The Sun and Moon are the most familiar lights in the heavens. This is true for all societies and for all of recorded history. The Suns energy is the source of life, and the bright full Moon enabled primitive societies to see at night and hunt for food. The Moon determines the tides, and this visible manifestation of its effects led astrologers to believe that the Moon determines our moodsindeed, the British Lunacy Act of 1842 defined a lunatic to be someone who was lucid during the two weeks prior to a full Moon and acted strange during the following fortnight. Belief that the Moons phases affect human affairs was widespread in the past and survives today. The Sun and Moon were central to the rhythm of ancient societies, as the regular motions of this pair through the sky, and the positions on the horizon where they rise and set, determined the seasons. In short, the motion of Sun and Moon relative to us on Earth provided the first reliable means of quantifying the calendar and gave order to human affairs.

The disappearance of either of these leading players in an eclipse threatened the natural harmony. For the ancient Greeks, an eclipse was explained as a sign that the gods were angry and was therefore regarded as a bad omen. So important and regular were the Sun and Moon that many societies elevated them to the status of gods. When a god vanished from the scene, some narrative explanation was called for. For the Tahitians an eclipse was a positive event: their explanation was that the Sun and Moon were making love. This optimism seems to have been the exception, however, with themes of a monster or beast devouring the Sun during a total solar eclipse being more common. The nature of the beast varied among cultures: a wolf in Nordic lands; a dragon in China; dogs in Central Europe.