Â鶹Éç

Edmund Halley  © Halley was an English astronomer and mathematician who was the first to calculate the orbit of the comet later named after him.

Edmond (sometimes Edmund) Halley was born on 8 November 1656 on the eastern edge of London. While at Oxford University, Halley was introduced to John Flamsteed, the astronomer royal. Influenced by Flamsteed's project to compile a catalogue of northern stars, Halley proposed to do the same for the Southern Hemisphere. To this end in 1676 he travelled to the South Atlantic island of St Helena. By the time he returned home in January 1678 he had recorded the celestial longitudes and latitudes of 341 stars and observed a transit of Mercury across the Sun's disk. Halley's star catalogue of 1678 was the first to contain telescopically determined locations of southern stars and in the same year he was elected a fellow of the Royal Society.

Along with the inventor and microscopist Robert Hooke, Sir Christopher Wren and Sir Isaac Newton, Halley was trying to develop a mechanical explanation for planetary motion. Although progress had been made, Hooke and Halley were not able to deduce a theoretical orbit that would match the observed planetary motions. However, Newton was already there. The orbit would be an ellipse, and Newton expanded his studies on celestial mechanics in his famous work of 1687, 'Philosophiae Naturalis Principia Mathematica', which Halley had persuaded him to publish.

In 1704, Halley was appointed Savilian professor of geometry at Oxford University, but continued his work in astronomy. In 1705, he published 'A Synopsis of the Astronomy of Comets', in which he described the parabolic orbits of 24 comets that had been observed from 1337 to 1698. He showed that the three historic comets of 1531, 1607, and 1682 were so similar in characteristics that they must have been successive returns of the same object - now known as Halley's Comet - and accurately predicted its return in 1758. In 1716, he devised a method for observing transits of Venus across the disk of the sun in order to determine accurately the distance of the Earth from the Sun. In 1720, Halley succeeded Flamsteed as astronomer royal at Greenwich, a position which he held until his death on 14 January 1742.