Thomas Henderson | |
|---|---|
 Thomas Henderson, c.1820s Scottish Astronomer Royal | |
| Born | (1798-12-28)28 December 1798 Dundee, Scotland |
| Died | 23 November 1844(1844-11-23) (aged 45) |
| Known for | distance toAlpha Centauri |
| Scientific career | |
| Fields | astronomy |
| Institutions | City Observatory, Edinburgh |
Thomas HendersonFRSEFRSFRAS (28 December 1798 – 23 November 1844) was a Scottish astronomer and mathematician noted for being the first person to measure the distance toAlpha Centauri, the major component of the nearest stellar system to Earth, the first to determine theparallax of a fixed star, and for being the firstAstronomer Royal for Scotland.
Born inDundee, he was educated at theHigh 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 lunaroccultation to measurelongitude he came to the attention ofThomas Young, superintendent of theRoyal 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 theRoyal Observatory at theCape of Good Hope inSouth 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 byManuel John Johnson of the East India Company's observatory onSaint Helena that the bright southern starAlpha Centauri had a largeproper motion, and Henderson concluded that it might be relatively close.[1]
The 1830s version of the "space race" was to be the first person to measure the distance to a star usingparallax, a task which is easier the closer the star. Henderson was thus in a good position to be this person. After retiring back to theUnited Kingdom due to bad health, he began analysing his measurements and eventually came to the conclusion that Alpha Centauri was just slightly less than oneparsec away, 3.25light years. This figure is reasonably accurate, being 25.6% too small.
Henderson did not immediately publish his results, however (there had been previous, discredited attempts to claim a measurement of stellar parallax), and eventually he was beaten to the punch byFriedrich Wilhelm Bessel, who published a parallax of 10.3 light years (9.6% too small) for61 Cygni in 1838.[2] Henderson published his results in 1839,[3] but was relegated to second place because of his lack of confidence. He later published confirming observations byThomas Maclear.[4] Alpha Centauri remained the nearest known star until the discovery ofProxima Centauri in 1915 byRobert T. A. Innes.
In the meantime, his measurement work at the Cape had led him to be appointed the firstAstronomer Royal for Scotland in 1834. The vacant chair of astronomy at theUniversity of Edinburgh was given to him on the advice of Prime MinisterLord Melbourne. From 1834 he worked at theCity Observatory (then called the Calton Hill Observatory) in Edinburgh until his death.[5] In April, 1840 he was elected aFellow of the Royal Society.[6]
Henderson became a member or fellow of several distinguished societies, including theRoyal Astronomical Society (1832) and theRoyal Society of Edinburgh (1834).[5]
He marriedAlexander Adie's daughter Janet Mary Adie (1808–1842) in 1836 and had one daughter, Janet Mary Jane Henderson (1842–1893) who is buried in theGrange Cemetery.[7]
He died at home 1 Hillside Crescent[8] in Edinburgh on 23 November 1844 and is buried inGreyfriars Kirkyard. The grave may be either in the grave ofAlexander Adie[9] or in a grave marked by the stone "to his memory".[10] His name is not recorded on the Adie grave; Adie himself died 14 years after Henderson.
A blue plaque is installed on his house at 1 Hillside Crescent. It refers to him as "Thomas J. A. Henderson".
A larger memorial (naming him "Thomas Henderson") is incorporated in the external wall of theCity Observatory.
Asteroid3077 Henderson is named in his honour.
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