Thomas Henderson (astronomer)

Thomas James Henderson
Thomas James Henderson, c.1820s Scottish Astronomer Royal
Born	(1798-12-28)28 December 1798 Dundee, Scotland
Died	23 November 1844(1844-11-23) (aged 45) Edinburgh
Nationality	Scottish
Fields	astronomy
Institutions	City Observatory, Edinburgh
Known for	distance to Alpha Centauri

Thomas James Alan Henderson FRSE FRS FRAS (28 December 1798 – 23 November 1844) was a Scottish astronomer and mathematician noted for being the first person to measure the distance to Alpha Centauri, the major component of the nearest stellar system to Earth, the first to determine the parallax of a fixed star, and for being the first Astronomer Royal for Scotland.

Born in Dundee, he was educated at the High School of Dundee, after which he trained as a lawyer, working his way up through the profession as an assistant to a variety of nobles. However, his major hobbies were astronomy and mathematics, and after coming up with a new method for using lunar occultation to measure longitude he came to the attention of Thomas Young, superintendent of the Royal Navy's "Nautical Almanac". Young helped the young Henderson enter the larger world of astronomical science, and on his death a posthumous letter recommended to the Admiralty that Henderson take his place.

Henderson was passed over for that position, but the recommendation was enough to get him a position at the Royal Observatory at the Cape of Good Hope in South Africa. There he made a considerable number of stellar observations between April 1832 and May 1833, including those for which he is remembered today. It was pointed out to him by Manuel John Johnson of the East India Company's observatory on Saint Helena that the bright southern star Alpha Centauri had a large proper motion, and Henderson concluded that it might be relatively close.