Features: October 2008

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Design by Howard Russell Butler, published as a supplement to the July-August 1926 issue of Natural History, of a triptych for the “Proposed Hall of Astronomy at the American Museum of Natural History.” It features three solar eclipses that he had observed in the United States (left to right): Oregon, June 8, 1918; California, September 10, 1923; and Connecticut-New York, January 24, 1925. Butler painted the eclipses based on sketches and notes of the colors he made in the brief time allowed.

Old Chinese bone inscriptions provide one of the earliest records of an eclipse—probably the one that, by our Western calendric reckoning, occurred October 22, 2134 b.c. Hsi and Ho, astronomers to the Emperor Chung K’ang, had failed to predict that eclipse, and as the Sun faded, pandemonium broke loose. The Son of Heaven had his court astronomers decapitated.

And there is at least one apparent reference to an eclipse in the Bible. In Amos 8:9, we read: “I will cause the Sun to go down at noon, and I will darken the Earth in the clear day.” Most likely that was the Eclipse of Nineveh, which has been dated June 15, 763 b.c. An Assyrian tablet also attests to the event.

Modern-day astronomers have learned much by studying solar eclipses, such as determining the precise relative positions of the Sun, Moon, and Earth. Certain kinds of studies—especially measurements of the Sun’s searing corona—can best be made during a total solar eclipse. The corona, or crown of the Sun, is a delicate halo of pearly white light that is always present but whose pale glow is normally overpowered by the Sun’s brilliance. (Because it is only visible during totality, it wasn’t until the eighteenth century that astronomers were certain that the corona surrounded the Sun and not the Moon!) It’s composed of highly diffuse, superheated, ionized gases; most scientists believe those gases extend all the way to Earth as the solar wind. Thus, understanding the corona is relevant to understanding our own environment.

During a total solar eclipse, a few ruby-red spots may seem to hover around the jet-black disk of the Moon. Those are solar prominences, tongues of incandescent hydrogen gas rising above the surface of the Sun. During the total eclipse of August 18, 1868, the French astronomer Pierre Janssen trained his spectroscope on the prominences and discovered a new chemical element. Two English astronomers, J. Norman Lockyer and Edward Frankland, later named it “helium,” from the Greek helios (the Sun). The gas was not identified on Earth until 1895.

And because sunlight is blocked during a total eclipse, some of the brighter stars and planets can be observed in the darkened sky. Under such conditions astronomers were able to test part of Einstein’s now-celebrated general theory of relativity. That theory predicted that light from stars beyond the Sun would bend from a straight path in a certain way as it passed the Sun. The positions of stars photographed near the Sun’s edge during a total eclipse on May 29, 1919, were compared with photographs of the same region of the sky taken at night; the results strongly supported Einstein’s theory.

I’ve often been asked, why bother traveling to an eclipse? My answer is always the same: “You must see one for yourself, and then you will understand.” Astronomy writer Guy Ottewell planned to create a painting of the 1983 eclipse visible from Borobudur in Java. He later wrote: “During the minutes of totality I was conscious of being in a different visual world; of trying to memorize colors for which I had no names, which would be as hard to recall or describe as a taste.”