Halley's Comet

In the late seventeenth century, comets were believed to follow parabolic (U-shaped) orbits and appear only once. The gregarious, outgoing Edmond Halley boldly suggested to his reclusive but genius friend, Isaac Newton, that comets may travel in an ellipse and appear more than once. Newton initially rejected the idea, even though his laws of motion and gravitation clearly allowed for such orbits. Later Newton accepted the possibility that comets can follow elliptical paths, orbiting the Sun repeatedly. In 1695, basing his work on Newton's laws of cometary motion, Halley computed the orbits of two-dozen comets, including the comet of 1682. He suggested the comets of 1531, 1607, and 1682 were one and the same, even venturing to predict its return in 1758. He was also the first to consider the perturbative (disruptive) effect of planets on a comet's orbit. Allowing for Jupiter's influence, he narrowed the comet's return to late 1758 or early 1759. Astronomers around the world anxiously watched the sky, aspiring to be the first to recover (find) the comet. On Christmas eve, 1758, German farmer and amateur astronomer, Johann Palitzch, spotted the comet which would forever bear Halley's name.