Scientists & Mathematicians : Edmund Halley

English mathematician, physicist, and astronomer who not only identified the comet later to be known by his name, but also compiled a star catalogue, detected stellar motion using historical records, and began a line of research that - after his death - resulted in a reasonably accurate calculation of the astronomical unit.

Halley was born in Haggerton, near London, on 8 November 1656. The son of a wealthy businessman, he attended St Paul's School (in London) and then Oxford University, where he wrote and published a book on the laws of Johannes Kepler that drew him to the attention of the Astronomer Royal, John Flamsteed. Flamsteed's interest secured for him, despite his leaving Oxford without a degree, the opportunity to begin his scientific career by spending two years on the island of St Helena, charting (none too successfully) the hitherto unmapped stars of the southern hemisphere. The result was the first catalogue of star positions compiled with the use of a telescope. On his return in 1678, Halley was elected to the Royal Society: he was 22 years old. For some years he then travelled widely in Europe, meeting scientists - particularly astronomers - of international renown, including Johannes Hevelius and Giovanni Cassini, before finally returning to England to settle down to research. He also became a firm friend of Isaac Newton. It may have been through Newton's influence that Halley in 1696 took up the post of deputy controller of the Mint at Chester. Two years later he accepted command of a Royal Navy warship, and spent considerable time at sea. In 1702 and 1703 he made a couple of diplomatic missions to Vienna before, in the latter year, being appointed professor of geometry at Oxford. His study of comets followed immediately. He succeeded Flamsteed as Astronomer Royal in 1720 and held the post until his death, at Greenwich, on 14 January 1742.

In St Helena, Halley first observed and timed a transit of Mercury, realizing as he did so that if a sufficient number of astronomers in different locations round the world also timed their observations and then compared notes, it would be possible to derive the distance both of Mercury and of the Sun. Many years later he prepared extensive notes on procedures to be followed by astronomers observing the expected transit of Venus in 1761. No fewer than 62 observing stations noted the 1761 transit, and from their findings the distance of the Sun from the Earth was calculated to be 153 million km/95 million mi - remarkably accurate for its time (the modern value is 149.6 million km/92.9 million mi).

Astronomy was always Halley's major interest. In the 1680s and 1690s he prepared papers on the nature of trade winds, magnetism, monsoons, the tides, the relationship between height and pressure, evaporation and the salinity of inland waters, the rainbow, and a diving bell; for some of the time he was also helping Newton both practically and financially to formulate his great work, the Principia; but these activities were all incidental to the pleasure he took in observing the heavens...