Arguably, total solar eclipses are a rare occurrence…they are visible somewhere on Earth about once every 18 months. Too often they cross over the empty Arctic region or the vast South Pacific where very few people can witness them. But this Monday, August 21, 2017, possibly the most people ever to witness a single eclipse will be treated to the “Great American Eclipse” as the Moon’s shadow travels coast-to-coast across the contiguous 48 states. Other kinds of eclipses happen—there are partial eclipses and annular eclipses—but the divinely designed “total” solar eclipse is rare.
A partial (l) and annular (r) eclipse.
A “partial” eclipse is when the Moon covers only part of the Sun’s face; during the upcoming eclipse, being too far from the path of totality here in the Philadelphia area, I will see only a partial eclipse…about 80% of the Sun will be covered.
For an “annular” eclipse, the Moon needs to be at its farthest from the Earth at the time of eclipse (the Moon travels in an ellipse around the Earth, not a circle, moving between 221,500 miles and 252,700 miles from Earth), so its shadow appears to be smaller than the face of the Sun, leaving a bright band—an annulus—of the Sun visible around the edges.
But a total eclipse is so uniquely, perfectly, randomly created that it meets all the criteria to be called “divinely designed.” Designed by a power in the universe that seemingly dares us to understand how the universe works. It’s a simple math equation that makes this true: the Sun is about 400 times larger than our moon, but it is also about 400 times farther away…the apparent disk sizes of the Sun and the Moon align perfectly.
During the minutes of a total eclipse, we can see and measure and try to understand things hidden to us in the normal light of day. The Sun’s corona, for example—that shadowy shimmering brightness that glows around the total eclipse—becomes visible only during the minutes of totality. Science has learned that the corona is about 5 million miles deep and burns at about 2 million degrees and is responsible for the solar wind (which, in turn, is responsible for the Aurora Borealis)…except during a total eclipse, this massive expanse of colossal energy is invisible to the naked eye.
Photograph from the total solar eclipse on May 29, 1919. The image of the star is moved by the Sun’s mass, just as Einstein predicted. The red dot shows where the star would have been without the sun's interference. (Credit: Royal Observatory, Greenwich)
A total solar eclipse was used in 1919 to prove Einstein’s Theory of Relativity…because during the eclipse, scientists could see and measure things that regular sunlight otherwise made impossible. They measured the positions of stars that appeared in the darkened sky near the eclipsed Sun and compared them to the positions of the same stars when, six months later, they appeared in the night sky; scientists learned—as Einstein had predicted—that the Sun’s mass “bent” space, making the stars appear to shift their place in the sky. The universe has always done it, Einstein imagined it, and the total eclipse made it visible…a divine design.
For me, eclipses make visible the very fact that we are adrift in a gigantic, mysterious, and divine universe. We live surrounded by a universe of space and time and laws and powers to which we are subject and from which we can/should learn. The world will change in response to the total eclipse, if only for the few minutes of totality: the power and scope of the Sun will be briefly visible; the grace and ease of the Moon’s motion around us will be briefly visible; weather will cool and animals will wind down as if night had quickly fallen; and many millions across this country will pause in their day to look skyward in wonder. Divine.