The smallest of the 12 constellations introduced at the end of the 16th century
by the Dutch navigators Pieter Dirkszoon Keyser and Frederick de Houtman. A
southern triangle had previously been shown 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 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.
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Triangulum Australe, with the alternative name Libella, the level, in Johann Bode’s Uranographia. 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
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