An insignificant constellation representing a pair of dividing compasses as used by geometers, draughtsmen and navigators for drawing circles and measuring distances. Circinus was introduced in 1756 under the name le Compas by the Frenchman Nicolas Louis de Lacaille, who fitted various figures into gaps between the existing constellations of the southern skies. In this case the gap seems to have been almost non-existent, and the compasses are squeezed in their folded position between the forefeet of Centaurus and Triangulum Australe. The name was Latinized to Circinus on Lacaille’s chart of 1763. The compasses are conveniently placed next to Triangulum Australe, a pre-existing constellation formed by Keyser and de Houtman which Lacaille visualized as a surveyor’s level, and Norma the set square, another of Lacaille’s inventions.

Circinus from the Uranographia of Johann Bode, with Triangulum Australe to its left and Norma et Regula (the set square and ruler) just off the top of the picture. For Lacaille’s original depiction, click here.

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