Thomas Henderson and α Centauri

The first observations containing evidence of a measurable stellar parallax were made by Thomas Henderson at the Cape of Good Hope in 1832/33. Although his response to Manuel Johnson's discovery in early 1833, that α Cen has a large proper motion, was to intensify observations for his remaining month at the Cape, Henderson apparently saw no urgency to reduce his observations. Instead he laboured through more routine matters, producing a catalogue of declinations of southern stars, improvements of refraction tables, and work on the solar and lunar parallaxes. It was Bessel's announcement of a determination of the parallax of 61 Cyg that finally stirred Henderson into action in late 1838.