Here comes Halley's. Scientists and laymen alike have golden opportunity to `marvel at the star'
FIRST the good news: Halley's comet is back from the dark, distant recesses of the solar system. Over the next few months, it will be visible in our skies as it pays its ``once in a lifetime'' visit to the vicinity of the sun. But don't expect too much of this rare celestial visitor. The bad news is that on this appearance the comet will be far from spectacular. In fact, it will appear fainter than on any of its previous recorded visits, stretching back over 2,000 years. As a result, astronomers are playing down their expectations this time around.Skip to next paragraph
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Halley's comet will, however, be bright enough to be visible to the unaided eye -- away from bright city lights. As seen from the deserts of Australia, it will be a memorable sight, if not an awesome one.
Despite its name, the comet wasn't actually discovered by Edmond Halley. He did, however, see its appearance in 1682. At that time most people still regarded comets as portents of doom. As Shakespeare had written earlier in the century: ``When beggars die, there are no comets seen; the heavens themselves blaze forth the death of princes.''
Astronomers knew that comets were celestial bodies moving between the planets, but they had no idea of the shape of comets' paths, and thought that each comet appeared only once.
Halley was a brilliant scientist, making original discoveries in physics, meteorology, and the earth's magnetic field. His expertise also went well outside the realms of pure science. He drew up the first tables of life expectancy, so providing the mathematical basis for life assurance; he built a practicable diving bell; and he undertook diplomatic work, including a little spying, for the British government.
But Halley's first love was astronomy, and he was eventually made Astronomer Royal -- at the grand age of 65.
Before this, he had discussed the problem of comets with his friend, the great physicist Isaac Newton. Newton had just formulated his law of gravitation, and showed that comets must go around the sun in long paths, either ellipses or open-ended parabolas. Halley calculated the paths of 24 comets, and he found that three of them had very similar orbits.
The comet that he had seen in 1682 seemed to be the same as one seen in 1607, which was possibly the reappearance of a comet observed in 1531. Halley predicted that it would reappear in another 76 years' time. On Christmas night 1758 -- well after Halley's death -- an astronomer in Germany did indeed pick up the comet as it returned to the sun -- and Halley's immortality was assured.
Halley's comet was first recorded by the Chinese, in 240 B.C., and we have records of every appearance since then. In A.D. 837, the comet was an awe-inspiring sight as it swept past the earth in the closest approach in history. Its most famous appearance, however, was in the early summer of 1066, just before King Harold of England was defeated by the Normans at the Battle of Hastings. In 1301, the Italian painter Giotto de Bondone saw Halley's comet, and portrayed it in a fresco as the Star of Bethlehem .
The comet's last appearance was in 1910. It was a brilliant sight, with a tail stretching a quarter of the way across the sky. The earth almost passed through the comet's tail, in fact, and doomsters predicted the end of the world -- although one entrepreneur benefited immensely by selling ``comet pills'' that would supposedly ward off any evil effects.
The comet is now heading in toward the sun, for its closest approach on Feb. 9, 1986. It is now visible from countries in the Northern Hemisphere. The best views from higher northern latitudes will be in December and January. In December, the comet appears high in the southern part of the sky, under the four stars that make up the great Square of Pegasus. The comet looks like a faint patch of light, visible to the naked eye (away from street lights) and easily seen through binoculars.
Later this month, the moon will be near the comet in the sky, and its brilliance will drown out the comet's feeble light.