By Tom Metcalfe
Total solar eclipses, when the moon nearly perfectly covers the sun, have fascinated humans since at least the time of the earliest civilizations. Some of the very oldest historical records, written on clay tablets in Babylonia around 2,500 years ago, are devoted to observations of eclipses. Astronomers at the time interpreted the events as omens of disaster, while folktales around the world typically explained eclipses as a conflict between the sun and a devouring celestial dragon, wolf or rat.
A few solar eclipses have even changed human history — for instance, by affecting the outcome of a pivotal ancient battle, or by inspiring scientists as they unlocked the secrets of humanity’s place in the universe. That’s a lot of responsibility for a phenomenon that astronomers sometimes describe as “a celestial coincidence.” After all, that’s what a total solar eclipse really is: a total coincidence.
“The [diameter of the] moon is almost exactly 400 [times] smaller than the sun’s diameter, and the sun is almost exact 400 times further away than the moon,” said Mark Gallaway, an astronomer at the University of Hertfordshire in the United Kingdom. “The consequence of this is that the angular diameter, or the size we see, of the sun and the moon in the sky are almost exactly the same.”
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