Genitive: Trianguli Australis
Abbreviation: TrA
Size ranking: 83rd
Origin: The 12 southern constellations of Keyser and de Houtman

One of the 12 constellations introduced at the end of the 16th century by the Dutch navigators Pieter Dirkszoon Keyser and Frederick de Houtman, and the smallest of them according to modern boundaries. A southern triangle had previously been shown in a completely different position, south of Argo Navis, on a globe of 1589 by the Dutchman Petrus Plancius, along with a southern cross, but they were not the constellations we know today. The modern Triangulum Australe was first depicted in 1598 on a globe by Petrus Plancius and first appeared in print in 1603 on the Uranometria atlas of Johann Bayer.

The three main stars of Triangulum Australe are brighter than those of their northern counterpart, although the constellation is smaller. Navigators have named its brightest star Atria, a contraction of its scientific name Alpha Trianguli Australis.

Triangulum Australe, with the alternative name Libella, the level, in Johann Bode’s Uranographia (1801). Bode followed Lacaille in showing a plumb bob attached to the triangle, thereby representing it as a surveyor’s level. Along with the compasses (Circinus) and a set square (Norma) it formed a group of surveying instruments in this part of the sky.

On his 1756 planisphere of the southern stars Lacaille referred to it as ‘le Triangle Austral ou le Niveau’ (‘niveau’ meaning level) and he even showed it with an attached plumb bob, indicating that he regarded it as representing a surveyor’s level. Later ‘niveau’ was Latinized to ‘libella’, as on Bode’s atlas shown here. Through some misreading, the historian R. H. Allen transferred the appellation ‘level’ to the nearby constellation Norma and termed that constellation the Level and Square (instead of the Rule and Square), thereby confusing generations of astronomers.

© Ian Ridpath. All rights reserved