Edmond Halley predicted his comet's return but died before it came back.
In 1705 Edmond Halley used Newton's new laws of gravity to argue that comets seen in 1531, 1607 and 1682 were one object returning roughly every 76 years. He predicted it would come back in 1758. He died in 1742. On Christmas Day 1758, a German farmer spotted it.
For most of history comets were seen as omens, and Aristotle taught they were disturbances in Earth's atmosphere. Tycho Brahe showed in 1577 that they lie far beyond the Moon, but many still thought they flew in straight lines. Then Isaac Newton published his laws of motion and gravity in 1687, and his friend and publisher Edmond Halley applied them to comets. Comparing 24 comet records, he noticed that the orbits of comets seen in 1531, 1607 and 1682 were almost identical, and concluded they were a single object.
Halley predicted a return in 1758. It was first seen again on 25 December 1758 by Johann Georg Palitzsch, an amateur astronomer and farmer. Three French mathematicians, Alexis Clairaut, Joseph Lalande and Nicole-Reine Lepaute, had calculated in advance that the pull of Jupiter and Saturn would delay its closest approach to the Sun, and they were right to within about a month. It was the first time anything other than a planet had been shown to orbit the Sun, and a triumphant early test of Newton's physics.
Records of the comet reach back to at least 240 BC. In 1066 it appeared before the Battle of Hastings and was stitched into the Bayeux Tapestry as an omen. Its orbit is a long ellipse, swinging from between the orbits of Mercury and Venus out to about the distance of Pluto, and its period has varied between about 74 and 80 years.
In March 1986 the European Space Agency's Giotto probe gave the first close look at a comet's nucleus. It found a peanut-shaped body about 15 kilometres long, broadly confirming Fred Whipple's 'dirty snowball' idea. One surprise was its colour: astronomers had expected it to be about as reflective as bare soil, but it is darker, reflecting only about 4 per cent of sunlight, similar to coal. Its next visit is due in mid-2061.
Source: Wikipedia — Halley's Comet · Text summarised from Wikipedia (CC BY-SA 4.0)
