Triangulum Australe’s name means “the southern triangle” in Latin, and its three brightest stars form an equilateral triangle. The constellation never sets below the horizon south of the equator, but is located too far south to be visible from Europe and most of the northern hemisphere.
The constellation has one star with a confirmed planet and one formally named star. The star name, as approved by the International Astronomical Union (IAU), is Atria. Atria is also the brightest star in the constellation, with an apparent magnitude of 1.91.
Triangulum Australe is not home to any Messier objects and no meteor showers are associated with the constellation.
History and Mythology of the Triangulum Australe Constellation
Triangulum Australe is not associated with any myths.
The constellation is the smallest of the 12 constellations created by the Dutch navigators Frederick de Houtman and Pieter Dirkszoon Keyser in the late 16th century. It first appeared on a a celestial globe in 1589, thanks to Petrus Plancius, where it was called Triangulus Antarcticus and incorrectly placed. It then appeared under its current name Triangulum Australe on Johann Bayer’s Uranometria in 1603
In Nicolas Louis de Lacaille’s 1756 map of the southern stars, he portrayed the constellations of Norma, Circinus and Triangulum Australe as a set square and ruler, a compass and a surveyor’s level respectively in a set of draughtsman’s instruments.
Location of the Triangulum Australe Constellation
Triangulum Australe is the 83rd largest constellation and occupies an area of 110 square degrees. It is located in the third quadrant of the southern hemisphere (SQ3) and can be seen at latitudes between +25° and -90°.
Its right ascension is 14h 56.4m to 17h 13.5m and its declination is −60.26° to −70.51°. It is best seen at 9pm during the month of July. Triangulum Australe culminates each year at 9pm on 23 August.
Triangulum Australe’s neighboring constellations are Apus, Ara, Circinus and Norma and it belongs to the Hercules family of constellations, along with Aquila, Ara, Centaurus, Corona Australis, Corvus, Crater, Crux, Cygnus, Hercules, Hydra, Lupus, Lyra, Ophiuchus, Sagitta, Scutum, Sextans, Serpens and Vulpecula.
Notable Stars
Atria
Atria, also known as Alpha Trianguli Australis, is the brightest star in Triangulum Australe and has an apparent magnitude of 1.91. With Beta and Gamma Trianguli, it forms the triangle asterism which gave the constellation its name.
Atria is located around 391 light years away from Earth and is thought to be around 48 million years old. It is an orange bright giant, thought to be a binary star, with the stellar classification of K2 IIb-IIa and a mass 7 times that of the Sun. Its diameter is 130 times that of the Sun and it is 5,500 times more luminous than the Sun.
Its name, Atria, comes from a contraction of its Bayer designation — A(lpha) Tri(anguli) A(ustralis).
Beta Trianguli Australis
Beta Trianguli Australis is the second brightest star in the constellation in Triangulum Australe and has a visual magnitude of 2.85. It is a double star composed of a yellow-white main sequence star belonging to the spectral class F1 V and a 14th magnitude line-of-sight companion separated from the primary by 155 seconds of arc. They are located around 40.37 light years away from the Sun. It forms the triangle asterism with Atria and Gamma Trianguli.
Gamma Trianguli Australis
Gamma Trianguli Australis is the third brightest star in the constellation in Triangulum Australe and has an apparent magnitude of 2.87. It is a white main sequence dwarf belonging to the spectral class A1 V and is located around 184 light years away from the Solar System.
It is the third star that forms the triangle asterism in Triangulum Australe along with Atria and Beta Trianguli. This star is thought to be around 260 million years old and has a radius 5.86 times that of the Sun. It is also a very fast spinner, with a projected rotational velocity of 199 km/s.
There is thought to be a circumstellar disk in its orbit, due to the fact it is emitting excess infrared radiation.
Delta Trianguli Australis
Delta Trianguli Australis is the fourth brightest star in the constellation and has an apparent magnitude of 3.86. It is a binary star composed of a yellow supergiant with the stellar classification of G2Ib-IIa, and the companion is a 12th magnitude star located 30 arc seconds from the primary. The entire system is located around 621 light years away from the Solar System.
Epsilon Trianguli Australis
Epsilon Trianguli Australis is a wide double star that consists of an orange giant of the spectral type K1-2III and a white main sequence star belonging to the spectral class A5, separated by 82.1 arc seconds. The system is located around 216.1 light years away from the Sun and has an apparent magnitude of 4.11.
The primary star has a visual magnitude of 4.11 while the companion has a magnitude of 9.32.
Zeta Trianguli Australis
Zeta Trianguli Australis is a spectroscopic binary star composed of a yellow-white dwarf belonging to the spectral class F6 V and a yellow dwarf with the stellar classification of G1 V, with an orbital period of 13 days. The system has an apparent magnitude of 4.90, is located around 39.5 light years away from the Sun and has a composite stellar classification of F9 V.
Eta Trianguli Australis
Eta Trianguli Australis is a blue-white subgiant star with the stellar classification of B7IVe and an apparent magnitude of 5.89. It is located around 690 light years away from Earth.
Theta Trianguli Australis
Theta Trianguli Australis is a yellow giant star belonging to the spectral type G8-K0III, with a visual magnitude of 5.50. It is located around 328 light years away from us.
Iota Trianguli Australis
Iota Trianguli Australis is a triple star system with an apparent magnitude of 5.28, located around 132 light years away from the Sun. In a 7.5 cm telescope, the system appears to be composed of a white and yellow star.
In fact, the system is a spectroscopic binary composed of two yellow-white class F stars with an orbital period of 39.8 days. One of these stars is a Gamma Doradus type variable star and thus the system’s brightness varies by 0.12 magnitudes over a period of 1.45 days. The third star is is a 10th magnitude star located 20 arc seconds away from the spectroscopic binary.
Kappa Trianguli Australis
Kappa Trianguli Australis is a yellow bright giant belonging to the spectral class G5IIa, with an apparent magnitude of 5.11. It is located around 1,207 light years away from the Sun.
X Trianguli Australis
X Trianguli Australis is a red carbon star with the stellar classification of C5.5 (Nb) and a mean apparent magnitude of 5.63. It is classified as a semi-regular variable with two periods of about 385 and 455 days, and its brightness ranges from magnitude 5.03 to 6.05.
X Trianguli Australis is located around 1,173 light years away from the Solar System. It has an absolute magnitude of -2.0 and a diameter about 400 times that of the Sun.
EK Trianguli Australis
EK Trianguli Australis is a dwarf nova of the SU Ursae Majoris type, composed of a white dwarf and a donor star that orbit around a common centre of gravity with a period of 1.5 hours. The white dwarf sucks matter from the other star onto an accretion disc and periodically erupts, reaching magnitude 11.2 in super outbursts, 12.1 in normal outbursts and remaining at magnitude 16.7 when quiet. The system is located around 586 light years away from the Solar System.
RT Trianguli Australis
RT Trianguli Australis is an unusual cepheid variable which shows strong absorption bands in molecular fragments of C2, ⫶CH and ⋅CN, and has been classified as a carbon cepheid of spectral type R. Its magnitude varies between 9.2 and 9.97 over a period of 1.95 days.
HD 133683
HD 133683 is a yellow-white bright giant star that belongs to the spectral class F6II and has an apparent magnitude of 5.77. Its absolute magnitude is -5.57 and it is about 6,037 light years away from us.
HD 147018
HD 147018 is a yellow dwarf with the stellar classification of G9V and an apparent magnitude of 8.4. It is located about 139 light years away from the Solar System and has 88 percent of the Sun’s mass.
In August 2009, two exoplanets, HD 147018 b and HD 147018 c, were discovered orbiting the star. The inner planet has a mass at least 2.12 times that of Jupiter and orbits the star with a period of 44.236 days, while the outer planet has at least 6.56 Jupiter masses and completes an orbit around the star every 1,008 days.
Deep Sky Objects
ESO 69-6
ESO 69-6 is a pair of galaxies that are currently in the process of colliding and merging with each other. They are located around 600 million light years away from the Solar System.
ESO 137-001
ESO 137-001 is a barred spiral galaxy that spans across 260,000 light years. It is located in the Norma Cluster, which lies in Triangulum Australe and Norma constellations.
NGC 6025
NGC 6025 is an open cluster that was discovered by the French astronomer Nicolas Louis de Lacaille in 1751-1752. It has an apparent magnitude of 5.1 and is located around 2,500 light years away from the Solar System. It is is about 11 light years in diameter and its brightest star is MQ Trianguli Australis with an apparent magnitude of 7.1.
NGC 5979
NGC 5979 is a planetary nebula with an apparent magnitude of 12.3. It was discovered in 1835 by John Herschel.
NGC 5938
NGC 5938 is a spiral galaxy that lies 5 degrees to the south of the star Epsilon Trianguli Australis, approximately 300 million light years away from Earth.
Henize 2-138
Henize 2-138 is a planetary nebula with a visual magnitude of 11.0. It is smaller in size than NGC 5979.
Extra Facts
- Johann Bode gave the constellation the alternative name, Libella (the level), in his Uranographia in 1801.
- German poet and author Philippus Caesius saw the three main stars as representing the Three Patriarchs, Abraham, Isaac and Jacob (with Atria as Abraham).
- The Wardaman people of the Northern Territory in Australia perceived the stars of Triangulum Australe as the tail of the Rainbow
- Serpent, which stretched out from near Crux across to Scorpius.
- The three-letter abbreviation for the constellation, as adopted by the International Astronomical Union in 1922, is “TrA”.
- The official constellation boundaries, as set by Belgian astronomer Eugène Delporte in 1930, are defined by a polygon of 18 segments.
Images:
Some Images created with the NightVision app – https://www.nvastro.com/nvj.html
Some Images created with the Stelvision Sky Map https://www.stelvision.com/en/sky-map/
Triangulum Australe 1- https://starregistration.net/constellations/triangulum-australe-constellation.html
Triangulum Australe 2 – https://en.wikipedia.org/wiki/Triangulum_Australe
NGC 6025 – http://www.phys.ttu.edu/~ozprof/6025f.htm
Triangulum Australe 3 – https://in-the-sky.org/data/constellation.php?id=83
ESO 69-6 – https://www.astrobin.com/full/304281/0/
ESO 137-001 -https://en.wikipedia.org/wiki/ESO_137-001
NGC 5979 – http://annesastronomynews.com/photo-gallery-ii/nebulae-clouds/ngc-5979/
NGC 5938 – https://cgs.obs.carnegiescience.edu/CGS/object_html_pages/NGC5938.html
Heinze 2-138 – http://www.sci-news.com/astronomy/science-pair-white-dwarfs-center-planetary-nebula-henize2428-02478.html