Halley, Edmond (1656–1742)

Portrait of the English astronomer Edmond Halley, who was Astronomer Royal after 1720. He was the first to predict the return of a comet (subsequently named after him), and he financed the publication of Isaac Newton's Principia.

The English astronomer and mathematician Edmond Halley at the age of 80 years, in a painting by the Swedish portrait-painter Michael Dahl. So keen was Halley's scientific curiosity that he learned Arabic in his fifties in order to be able to translate the works of the Greek mathematician Apollonius of Perga (3rd century BC), many of which were available only as medieval Arabic texts.

English astronomer. He not only identified the comet that was later to be known by his name, but also compiled a star catalogue, 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 comet 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 in 1705 in his Synopsis Astronomia Cometicae that it would reappear in 1758. When it did, public acclaim for the astronomer was such that his name was irrevocably attached to it.

He made many other notable contributions to astronomy, including the discovery of the proper motions of the stars named Aldebaran, Arcturus, and Sirius, and working out a method of obtaining the solar parallax by observations made during a transit of Venus across the Sun. He was Astronomer Royal from 1720.

Halley was born near London, and studied at Oxford but left in 1676 without finishing his studies and taking a degree. He spent 1676–78 on the South Atlantic island of St Helena, charting the stars of the southern hemisphere. The result was his Catalogus Stellarum Australium (1679), which was incorporated in the third volume of Flamsteed's Historia Coelestis (1725). He was secretary of the Royal Society from 1685 and editor of its Transactions. He became professor of geometry at Oxford in 1703.

He was also a pioneer geophysicist and meteorologist and worked in many other fields, including mathematics and archaeology. He was a friend of the scientist Isaac Newton, and worked in some similar areas. Among the problems that attracted Halley's attention was that of the proof of Kepler's laws; having progressed some way, he went to Cambridge to consult Newton and found that he had already solved the problem but had published nothing. It was thus at Halley's urging and at his expense that the Principia (1698–1700) was published.

Halley was the captain of HMS Paramour Pink 1698–1700, a small vessel that he used to observe the magnetic variation (the deviation of the compass from true north) over the Atlantic Ocean from 52° north to 52° south, in the hope that he might be able to use the information as a means of determining longitude. He published his observations in a General Chart of the Variation of the Compass (1701), the first such chart to be published and the first on which isogonic lines (having equal angles), or, as they were called, Halleyan lines, appeared.

In common with many of the leading mathematicians and scientists of the 17th century, Halley was responsible for a wide variety of major breakthroughs that changed human understanding of the Earth and the universe, working in fields from astronomy, geophysics, and mathematics to archaeology. Halley played an active part of a pioneering and interacting community that was pushing forward the boundaries of knowledge; this was exemplified by his friendship with Newton and membership of the Royal Society.