Rendezvous with the Sun

"Hey, look! It's right out there," exclaimed Skylab Astronaut Edward Gibson last week. "I tell you, it's one of the most beautiful creations I've ever seen. It's so graceful." Added Skylab Commander Gerald Carr: "It's yellow and orange, just like a flame."

After a journey of billions of miles across the outer reaches of the solar system, the comet called Kohoutek last week finally made its solar rendezvous. And for the first time in astronomical history, a comet's close sweep round the sun--when it is subject to maximum heat and gravitational force--was observed from above the earth's obscuring atmosphere. As they completed their sixth week in orbit, the crew of Skylab 3 made the most of the opportunity.

Equipped with cameras and other scientific gear, the astronauts spent two lengthy observation periods outside their orbital lab. The first--on Christmas Day --covered the interval just before the comet disappeared in the sun's glare, approaching to within some 13 million miles of the sun at speeds of over 250,000 m.p.h.; the second took place after Kohoutek skimmed just across the top of the solar disc. The comet was so close to the sun that they could not see it during their first space walk. But at week's end they more than made up for the loss. Almost as soon as they stepped out of their orbital lab for the second walk, they spotted the comet, glowing brighter than ever. By properly aiming cameras that were specially equipped to block the glare, they took dozens of pictures in different colors--not only of Kohoutek but also of the huge halo of hydrogen gas that surrounds it.

Less Dusty. Scientists must wait to assay this scientific treasure until the crew returns to earth with the film in February, at the end of the 84-day mission. But even from the ground, scientists gathered an enormous amount of data about the comet--perhaps the most intensively observed celestial object in the annals of astronomy.

By taking continuous infra-red (or heat) pictures, for instance, a University of Arizona team led by Astronomer Frank Low determined that as Kohoutek sped toward the sun, it was heated from minus 94DEG F. to as high as 900DEG F. in less than three months. A colleague at the University of Arizona, Astronomer Elizabeth Roemer, speculated that Kohoutek may be less dusty than other comets making their first pass round the sun. Otherwise, the dust being boiled off Kohoutek would have produced a more spectacular tail. Perhaps the most intriguing find was made by a radio telescope atop Kitt Peak: while scanning Kohoutek, it picked up the telltale "signature" of methyl cyanide. Another place where that organic compound has been found is in the giant clouds of interstellar dust and gases in which new stars and planetary systems may be forming--one more clue that comets trace back to the solar system's infancy.

Before the encounter, Astronaut Carr spotted a puzzling red color in the comet's tail. That may mean that Kohoutek has more moisture than most comets, for this tint suggests concentrations of hydrogen and oxygen, the two components of water. In other respects, Kohoutek's twin tails--one composed of dust particles, the other of glowing gases --seem to be developing normally. As the comet began its hairpin turn round the sun, the dust tail blown by the slight pressure of sunlight continued to trail behind. But the plasma tail, interacting with the solar wind, moved out in front.

Astronomers are still in disagreement about how bright the comet will appear to viewers on earth. Elizabeth Roemer, for one, doubts that Kohoutek will live up to its earlier billing as "comet of the century." Other scientists are still confident that the comet will put on a good celestial show. In any event, Kohoutek should become visible to the naked eye early in January--about an hour after sunset, just above the southeastern horizon--and could continue to put on a spectacular performance until the middle of the month.

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