A total eclipse of the Sun almost makes me believe in God.
Barring unforeseen circumstances, I’ll be in Missouri on August 21 to see my fifth one of these things, but my first since 1979. A total solar eclipse is, hands down, the most extraordinary natural event I’ve ever witnessed. For a few minutes, you can see where you are in space: on a ball of rock circling a ball of fire, with a smaller ball of rock passing between. That’s you, standing in the shadow it casts.
The shadow is only about 70 miles wide, which explains why solar eclipses, while they occur at least every two years, rarely touch the same spot twice in an average human lifetime. You usually have to make an effort to see one.
We Earthlings are fortunate to see them at all. We live on the only planet in the Solar System – and possibly the galaxy – that puts on this kind of show.
During the few minutes of totality, the disk of the Sun is hidden behind the Moon, but you can see the Sun’s atmosphere, or corona, shimmering around it. At this time it is perfectly safe to look at. The danger to your eyes in an eclipse occurs in the moments before and after totality, when you are looking at a sliver of direct sunlight that doesn’t hurt your eyes but can damage them.
Other planets have moons, but they are either too large or too small or too close or too distant to cover the sun exactly. From the surface of the Earth, the Moon and the Sun are the same apparent size. There is no requirement of physics to explain this.
But the distances between Earth and Moon are not constant, because orbiting bodies move in ellipses, not circles. When a solar eclipse occurs near the Moon’s apogee (farthest distance from Earth) and/or Earth’s perihelion (closest approach to the Sun), the disk of the Moon is not big enough to cover the Sun, resulting in an annular, or ring eclipse, similar to a partial eclipse in that it doesn’t get dark.
Furthermore, the Moon is moving slowly away from Earth. The pace is beyond glacial, but in a few million years, there will be no more total solar eclipses. The concurrence of humanity’s emergence and perfect eclipses troubles some scientists. In his excellent 2011 book Alone in the Universe: Why Our Planet is Unique (Wiley), John Gribben explains:
“Just now, the Moon is about 400 times smaller than the Sun, but the Sun is about 400 times farther away than the Moon, so that they look the same size on the sky. At the present moment of cosmic time, during an eclipse, the disc of the Moon almost exactly covers the disk of the Sun. In the past, the Moon would have looked much bigger, and would have completely obscured the Sun during eclipses; in the future, the Moon will look much smaller from Earth and a ring of sunlight will be visible even during an eclipse. Nobody has been able to think of a reason why intelligent beings capable of noticing this oddity should have evolved on Earth just at the time that the coincidence was there to be noticed. It worries me, but most people seem to accept it as just one of those things.”
It doesn’t worry Caleb Scharf, Director of Astrobiology at Columbia University. In a 2012 blog for Scientific American titled The Solar Eclipse Coincidence, he wrote:
“Is there some great significance to the fact that we humans just happen to exist at a time when the Moon and Sun appear almost identically large in our skies? Nope, we’re just landing in a window of opportunity that’s probably about 100 million years wide, nothing obviously special, just rather good luck.”
Do coincidences happen? Probability dictates that they must. California’s Bay Area experienced its biggest earthquake since 1906 in the middle of the only World Series ever played between San Francisco and Oakland, but that doesn’t mean the ballgame caused the quake.
Perhaps we’re here because of an extraordinary run of good luck, akin to flipping a hundred heads in a row, something that might happen only once in the lifetime of the Universe. Our spectacular solar eclipses might be the result of similar luck.
Or just maybe, some ancient intelligence we don’t yet understand placed the Earth, Moon and Sun just so, to nudge a curious species toward contemplating the Cosmos. As though we were meant to reach for the stars, from the start.
Who knows? I certainly don’t.