 Edinburgh's City Observatory |
Thomas James Henderson lived from 28 December 1798 to 23 November 1844. He was the first Astronomer Royal for Scotland. The wider picture in Scotland at the time is set out in our Historical Timeline.
Thomas James Henderson was born in Dundee and educated at the High School of Dundee. He went on to train as a lawyer, though his real love lay with mathematics and astronomy. His discovery of a new way of measuring longitude using lunar occultation brought him into contact with Thomas Young, the producer of the Royal Navy's "Nautical Almanac". With Young's encouragement, Henderson moved away from the law and into astronomy.
When Thomas Young died, he left a letter recommending Henderson as his successor. The Admiralty did not act on the recommendation, but Henderson was instead offered a post at the British observatory which had been established at the Cape of Good Hope in South Africa. Between April 1832 and May 1833 he made many observations, and came to the conclusion that the brightest star in the southern constellation of Centaurus, Alpha Centauri, might be relatively close to Earth (compared to most other stars) because it had a large "proper motion", ie it seemed to move over time relative to the more static stellar background. This led to the thought that it might be possible to measure the distance to Alpha Centauri using parallax, the star's apparent change of location as the Earth moved through its orbit around the sun.
After returning to Scotland through ill-health, Henderson drew on his South African observations to calculate that Alpha Centauri was just slightly less that one parsec away, or a little over 3 light years distant. This was not bad, as modern calculations place it at 1.34 parsecs or 4.37 light years away. Henderson only published his results in 1839, the year after Friedrich Wilhelm Bessel had published a calculated distance to another star using the same method.
In 1834, Henderson was appointed to be the first Astronomer Royal for Scotland, from a base at Edinburgh's City Observatory on Calton Hill. He was also made Professor of Astronomy at the University of Edinburgh. He continued in both posts until his death in 1844. He is buried in Greyfriars Kirkyard.
