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Born in Dundee, Scotland, he was trained as a lawyer and worked 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 British Navy's "Nautical Almanac". Young helped 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 as the British observatory at the Cape of Good Hope in South Africa. There he made a considerable number of stellar observations between April 1832 and May 1833Events January 3 Britain seizes control of the Falkland Islands in the South Atlantic. June 6 U. President Andrew Jackson becomes the first President to ride a train. September 29 The infant Isabella II becomes Queen of Spain, under the regency of her mot, including those for which he is remembered today. It was pointed out to him that the bright southern star Alpha Centauri had a large proper motionProper motion is a component of the motion of stars. At first sight the stars seem to be in fixed positions with respect to each other, meaning they always form the same figures, and (for example) Ursa Major looks the same now as forty years ago. More car, and Henderson concluded that it might be a close star.

The 1830s version of the "space race" was to be the first person to measure the distance to a star using parallaxParallax is the change of angular position of two stationary points relative to each other as seen by an observer, due to the motion of said observer. Or more simply put, it is the apparent shift of an object against a background due to a change in observ, a task which is easier the closer the star. Henderson was thus in a good position to be this person. After retiring back to the United KingdomThe United Kingdom of Great Britain and Northern Ireland is a state in Western Europe, usually known simply as the United Kingdom the UK Britain or less accurately as Great Britain . The UK was formed by a series of Acts of Union which united the formerly due to bad health, he began analyzing his measurements and eventually came to the conclusion that Alpha Centauri was just slightly less that one parsecThis article is about the unit of length. In computer programming, Parsec is an XML syntax analyzer, like Lark, or a parsing library for the Haskell programming language. There's an open source computer game named Parsec . The parsec (abbreviated pc is a away, 3.25 light yearA light year abbreviated ly is the distance light travels in one year: roughly 9. 46 × 1012 kilometres (9. 46 petametres, or about 5. 88 × 1012 miles). More specifically, a light year is defined as the distance that a photon would travel, in free space ans. This figure is reasonably accurate, being 33.7% too small.

Doubts about the accuracy of his instruments kept him from publishing, however (there had been previous, discredited attempts to claim a measurement of stellar parallax), and eventually he was beaten to the punch by Friedrich Wilhelm Bessel, who published a parallax of 10.4 light years (9.6% too small) for 61 Cygni61 Cygni is a star in the Cygnus constellation. Though it is among the least conspicuous of stars visible in the night sky to an observer without an optical instrument, 61 Cygni attracted the attention of astronomers due to its large proper motion. The st in 1838. Henderson published his results in 1839, but was relegated to second place because of his lack of confidence.

In the meantime, his measurement work at the Cape had led him to be appointed the first Astronomer Royal in 1834. The private observatory on Calton Hill in Edinburgh — where he had made his first observations as an astronomer — was sold to Edinburgh University and the vacant chair of astronomy there given to him on the advice of Prime Minister Lord Melbourne.