Thursday, December 25, 2008

Halley's Comet - The Christmas Connection


Edmund Halley's resume is one of the most impressive in the history of science. He compiled the first atlas of the stars of the southern hemisphere. He measured Earth's magnetic field, and even invented the basis for life insurance.

Yet Halley's enduring claim to fame was solidified well after his death. In fact, it happened 250 years ago today.

Halley was a friend of Isaac Newton, who had devised laws of motion and gravity. The planets and moons all followed these laws just fine, but no one was sure if comets would do the same thing.

Comets are mountain-sized balls of rock and frozen gases that grow long tails as they approach the Sun. In Halley's time, though, their nature was poorly understood. In fact, no one was sure if they continuously orbited the Sun, as planets do, or if they disappeared into space after a single appearance.

Halley plotted the motions of about two dozen comets that had appeared in recent centuries. He found that the comets of 1531, 1607, and 1682 all followed the same path -- suggesting that they were a single body. Since the appearances were about 75 years apart, Halley predicted that the comet would return in 1758.

Halley died in 1742. But on Christmas Day of 1758, a German amateur astronomer, Johann Palitzsch, first saw the comet on its return to the inner solar system. Astronomers named the comet in Halley's honor -- adding one final listing to his impressive resume.

More here.

Image source: National Geographic


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