Light on the Sun

Meeting at Harvard Observatory, a small group of leading U.S. astronomers agreed last week that a Swedish physicist, Bengt Edlen, had just thrown a good deal of light on the sun. It concerned the nature of the sun's corona--its turbulent halo of incandescent gases.

Great tongues of flame leap from the sun, a half-million miles into space, sink back and leap again. Sometimes, strangely, clouds of gases appear out of nowhere far above the sun and blazing streamers lick back toward the sun's surface like prankish backward-movies of a high diver. What elements, astronomers have puzzled, form the corona? Where do the backward-flowing flames come from?

The corona is bright, but the sun itself outdazzles it except when blacked out by the moon (or by synthetic eclipses created by the device called a coronagraph). Since each of the 92 standard elements, when hot, glows with distinctive spectrum colors, astronomers can analyze the corona's chemical content with spectroscopes during eclipses. They have found in it about two dozen unidentifiable spectrum bands.

Some astronomers once thought these indicated a new element, "coronium." Others suspected were light elements like oxygen in a high state of atomic excitation.

But Physicist Edlen demonstrated that the corona probably consists mostly of heavier elements like iron, calcium, nickel. This was a big surprise to astronomers. Surprise No. 2 was Edlen's calculation that this high excitation which causes such heavy atoms to give off new spectrum lines must indicate coronal temperatures of 2,000,000DEG F.

Scientists had formerly assumed the corona to be scarcely hotter than the sun's surface, a mere 10,000DEG F. Physicist Edlen was so astonished by his own conclusions that he kept them secret for two years while he cleared up all reasonable doubts.

Verification seemed near last week. Harvard Observatory's Donald Howard Menzel amplified Edlen's theory with data from his Siberian eclipse expedition in 1936 and from Harvard's coronagraph observatory at Climax, Colo. Inside the sun, atoms are so highly ionized--having most of their electrons wrenched away from their nuclei--that they are not matter as we know it but rather invisible, sub atomic debris. These hot, degenerate gases are expanded, Menzel believes, by the force of great whirlpools within the sun. Therefore, streaming out of the sun's interior in occasional eruptions, the gases do not cool immediately. Far from the sun's surface, they retain much of the heat of the sun's interior, and they are still so highly ionized as to be invisible. But as they cool, the atoms become less ionized, and electrons rejoin their nuclei. Visible matter condenses apparently out of nothing into flaming tongues that rain downward toward the sun.

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