Two Years at the Cape

Nicolas-Louis de Lacaille was an abbe and a professor of mathematics, and in 1751 he took an observatory to Table Bay and spent two years working the southern sky from Cape Town. In that time he recorded positions for close to ten thousand stars, most of which had never been catalogued, using a small refractor on a quadrant and observing night after night through a hole in the roof of a hut he had built. He also measured an arc of the meridian in the Cape hinterland and, in coordination with an observer in Europe, made simultaneous observations of the moon and the planets to improve the value of their distances.

The catalogue is the reason the southern sky is mapped at all in the European tradition. Ptolemaic astronomy had been built from the Mediterranean and had never seen the region round the southern pole, and the constellations that navigators had sketched into it in the sixteenth and seventeenth centuries were incomplete and inconsistent. Lacaille filled the gap systematically and added fourteen constellations of his own, and he also broke up the huge ancient figure of the ship Argo into a keel, a stern and a set of sails, which is why no constellation called Argo exists on a modern chart.