Halley and His Comet

Edmond Halley, the British astronomer Royal whose name is immortalized by a certain popular comet, was born on November 8, 1656.

Before Halley observed his famous namesake, the comet that bears his name visited the inner solar system regularly since at least 240 B.C. Yet not one understood that comets orbits the Sun. It was believed that these mountain-sized chunks of frozen gas and dust appeared only once and then vanished. Many even thought that comets were freakish storms high in Earth’s atmosphere.

Halley, a gentleman adventurer who explored the seas, studied the atmosphere, and charted the skies, developed an interest in comets when he saw the very bright comet of 1680 while in Paris. He got the records of its movements from the director of Paris Observatory and tried – without success – to calculate the comet’s orbit.

Later, Halley befriended Isaac Newton, the physicist and mathematician who devised the three laws of motion and the law of universal gravitation. Halley later convinced Newton to record his work in a volume known as the Principia, and he even paid for the book`s publication.

Newton told Halley that he believed comets circle the Sun in elliptical orbits. Using Newton`s laws, Halley computed the orbits of twenty-four comets. He found that the comets of 1456, 1531, 1607, and 1682 had very similar orbits. Halley decided they represented just one object, and he predicted that the comet would return in 1758.

And it did. On Christmas night 1758, sixteen years after Halley`s death, amateur astronomer George Palitzsch saw the comet on its way toward a rendezvous with the Sun in early 1759.

polar cap mars

The South Polar Cap of Mars