(1656-1742) English atronomer who not only identified 1705 the comet that was later to be known by his name, but also compiled a star catalog, detected the proper motion of stars, using historical records, and began a line of research that—after his death—resulted in a reasonably accurate calculation of the astronomical unit.
Halley calculated that the cometary sightings reported in 1456, 1531, 1607, and 1682 all represented reappearances of the same comet. He reasoned that the comet would follow a parabolic path and announced 1705 that it would reappear 1758. When it did, public acclaim for the astronomer was such that his name was irrevocably attached to it.
Halley was also a pioneer geophysicist and meteorologist and worked in many other fields including mathematics. He was a friend of Isaac Newton, whose Principia he financed.
Halley was born near London and studied at Oxford but left without taking a degree. He spent 1676–78 on the S Atlantic island of St Helena, charting the stars of the southern hemisphere. He became professor of geometry at Oxford 1703.