TrA · Trianguli Australis
Triangulum Australe Constellation
IAU constellation mapTrATriangulum Australe (TrA) is one of the 88 constellations recognised by the International Astronomical Union. It covers 110 square degrees of the southern sky in quadrant SQ3. Its brightest star is Atria. The Latin genitive of the name is Trianguli Australis, used to form star names within the constellation. The IAU standardised all constellation boundaries in 1930.
Quick facts
- IAU name
- Triangulum Australe
- Abbreviation
- TrA
- Latin genitive
- Trianguli Australis
- Hemisphere
- southern
- Area
- 110 sq deg
- Brightest star
- Atria
- Quadrant
- SQ3
- Family
- Bayer
- Mythology origin
- Modern
- Discovery era
- Keyser and de Houtman, 1597-1598 (Bayer 1603)
Mythology
The Southern Triangle was introduced by the Dutch navigators Keyser and de Houtman during their 1595–1597 expedition and published by Johann Bayer in Uranometria (1603). Earlier references appear in the works of the Italian explorer Amerigo Vespucci, who may have described the southern triangle of bright stars in his account of his voyages around 1503. The constellation forms a compact, nearly equilateral triangle — the most regular triangle in the sky — easily identifiable from southern latitudes. Its brightest star, Atria (Alpha Trianguli Australis), is an orange giant of magnitude 1.91 — the 42nd-brightest star in the sky — lying about 415 light-years from Earth. Triangulum Australe is best observed in June near the Southern Cross.
Overview
Triangulum Australe is one of the 88 constellations formally recognised by the International Astronomical Union (IAU). It occupies 110 square degrees of sky in the southern hemisphere sky, best visible at latitudes between +45 and -90 degrees in June. The constellation belongs to the Bayer family of constellations. Its Latin genitive is Trianguli Australis, the form used when naming stars within the constellation — for example, the brightest star Atria may appear in catalogues as Alpha Trianguli Australis or similar. The IAU standardised the boundaries of all 88 constellations in 1930 under the direction of Eugène Delporte, using straight lines of right ascension and declination to eliminate the ambiguities of earlier variable-boundary systems.
Notable stars
The brightest star in Triangulum Australe is Atria. Individual stars within Triangulum Australe are conventionally named using Bayer designation — Greek letters followed by the Latin genitive of the constellation name (Trianguli Australis) — introduced by Johann Bayer in his 1603 star atlas Uranometria. Flamsteed numbers (numeric designators followed by Triangulum Australe) were added by John Flamsteed in his 1712 catalogue. Variable stars, double stars, and deep-sky objects within the Triangulum Australe boundary are catalogued by the IAU with the abbreviation TrA.
History and catalogue
Triangulum Australe was introduced or documented by Keyser and de Houtman, 1597-1598 (Bayer 1603). The modern IAU constellation boundaries were formally established in 1930. The designation TrA is the official three-letter IAU abbreviation used in star catalogues, variable star designations, and positional references. The family classification 'Bayer' groups this constellation with others sharing a region of sky or a common historical source in astronomical literature.
Sources & further reading (2)
- official-iau — accessed 2026-05-06
- encyclopedia — accessed 2026-05-06
Frequently asked questions
What does the name Triangulum Australe mean?
Triangulum Australe is the Latin name used by the IAU to designate this constellation. The name comes from classical Latin and Greek astronomical tradition. In star catalogues, stars within Triangulum Australe are designated using the genitive form of the name (e.g. Alpha Triangulum Australe or similar Latin genitive forms) — a naming convention introduced by Johann Bayer in his 1603 atlas Uranometria and still in use today.
How large is Triangulum Australe compared to other constellations?
Triangulum Australe covers 110 square degrees of sky. The full sphere of the sky contains 41,253 square degrees, so Triangulum Australe occupies about 0.3% of the total sky. For comparison, the largest constellation is Hydra at 1303 square degrees; the smallest is Crux at 68 square degrees.
When and where is Triangulum Australe visible?
Triangulum Australe is primarily a southern hemisphere constellation. Observers at high northern latitudes cannot see it; it is best appreciated from the southern tropics or high southern latitudes. The brightest star, Atria, serves as the main visual anchor for locating the constellation. As with all constellations, the best viewing conditions are a dark sky away from artificial light pollution, with the constellation high enough above the horizon to minimise atmospheric absorption.
