Eclipses of 1940

Where were Hsi and Ho? Where were the court astronomers? On this day in ancient China, some two millenniums before Christ, a monster was seen devouring the sun. While people rushed about madly and beat drums to scare off the celestial demon, Court Astronomers Hsi and Ho were found drunk. To punish them for being "sunk in wine and excess" instead of tending to business on a dire occasion, they had their heads cut off.

Astronomers no longer get either drunk or decapitated during eclipses. Now they have a healthy interest--especially in total eclipses of the sun, for during the fleeting moments of totality they get their best view of the sun's prominences, feathery spurts of incandescent gas rising to heights of hundreds of thousands of miles from the solar surface; and of the corona, the sun's pearly outer envelope.

Since 1868 astronomers with wide-slit spectroscopes have been able to see the prominences without benefit of eclipse, and in recent years the prominences have been studied and photographed regularly with spectrohelioscopes and spectroheliographs. Bernard Lyot of France, operating a special telescope from a mountain in the Pyrenees, managed to chart the corona of the uneclipsed sun, and Bell Telephone Laboratories have lately designed an instrument called the "Coronaviser," which sidetracks the light from the body of the sun, then scans the prominences and corona with a television pickup. But nothing equals one of Nature's own blackouts.

The solar and lunar eclipse schedule for 1940 lists five events, which is higher than the average. The maximum possible number of eclipses in a year is seven (as in 1935) and the minimum is two. There must be at least two solar eclipses every year, but a year can pass without any lunar eclipses at all.

Last week the first event took place, a partial eclipse of the moon. It was invisible to the naked eye, because the earth's penumbra (zone of partial shadow) barely nicked the moon's outer edge. There is no "path" in lunar eclipses; when the moon enters the earth's shadow, the effect is visible from the whole hemisphere facing the moon's direction. Two other partial lunar eclipses will occur during 1940: a conspicuous, nearly total one, visible everywhere in the U. S., on April 21; an inconspicuous one on Oct. 16.

On April 7 there will be an annular eclipse of the sun. An annular eclipse occurs when the moon's image, though centred against the sun's disk, is too small to cover it entirely, leaving a ring of bright light around the edge. The images of the sun and moon are nearly the same size in the sky, but the distance of both bodies from earth varies slightly, and the size of their apparent disks varies accordingly. April's annular eclipse begins in the Pacific, crosses the southern U.S. --darkening Austin, Houston, Baton Rouge, New Orleans, Pensacola, Tallahassee, Savannah, Jacksonville--and ends in the Atlantic (see chart}. Texas' McDonald Observatory, which is 50 miles from the shadow path, will send a party into the path near the Mexican border to study infra-red radiation from the bright ring around the moon.

The No. 1 attraction will be staged Oct. 1--a total eclipse of the sun, beginning in the Pacific, crossing South America, the South Atlantic, South Africa, and ending in the Indian Ocean. Because it crosses wide stretches of land, its shadow path will probably be as heavily studded with astronomers' camps as that of the total solar eclipse which four years ago swept clear across Asia (TIME, June 22, 1936).

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