Constellations of the Month: July – Triangulum Australe:
We continue July with the last constellation of the month, Triangulum Australe, “The Southern Triangle.”

Triangulum Australe constellation map courtesy of Openverse

Triangulum Australe, “The Southern Triangle” – The constellation of Triangulum Australe is located in the southern hemisphere, and its symbolism translates to “the southern triangle” in Latin. The constellation has three most luminous stars within the constellation create an equilateral triangle. Triangulum Australe was established by the Dutch astronomer Petrus Plancius during the late 16th century, with its first representation appearing in 1603 in Johann Bayer’s Uranometria. This constellation is positioned too far south to be observed from Europe and the majority of the northern hemisphere; however, it never descends below the horizon south of the equator.

NGC 5979 courtesy of Openverse

Key points regarding Triangulum Australe:

• Meaning: The term “Triangulum Australe” translates to “The Southern Triangle” in Latin. The constellation Triangulum Australe features a single star that has a confirmed planet and does not include any Messier objects. The constellation’s brightest star is Atria, designated as Alpha Trianguli Australis, which has an apparent magnitude of 1.91. Additionally, there are no meteor showers linked to this constellation. Within Triangulum Australe, there exists one star that has been formally named. The name of this star, which has received approval from the International Astronomical Union (IAU), is Atria. The deep sky objects found in Triangulum Australe comprise the planetary nebulae NGC 5979 and Henize 2-138, the interacting galaxies ESO 69-6, the open cluster NGC 6025, the spiral galaxy NGC 5938, and the Jellyfish Galaxy (ESO 137-001), which is part of the Norma Cluster.
• Notable stars: Alpha Trianguli Australis is the brightest star in the Triangulum Australe constellation, with an apparent magnitude of 1.91 and located about 391 light years from Earth. It is an orange bright giant, approximately 48 million years old, with a mass around seven times that of the Sun and significantly greater luminosity. It is believed to be a binary star. Beta Trianguli Australis is the second brightest star in the constellation, with a visual magnitude of 2.85 and a distance of about 40.37 light years. It is a double star consisting of a yellow-white main sequence star and a faint companion. Gamma Trianguli Australis, the third brightest star, is a white main sequence dwarf with a magnitude of 2.87 and a distance of about 184 light years. It shows rapid rotation and has similar excess infrared emissions indicating a circumstellar disk. Other notable stars include Delta Trianguli Australis, a binary yellow supergiant, and Epsilon Trianguli Australis, a wide double star system. Zeta, Kappa, and Iota Trianguli Australis feature different stellar classifications and distances, while Theta is a yellow giant. X Trianguli Australis is a red carbon star, and HD 133683 is a bright giant. Finally, Eta Trianguli Australis, HD 147018, and EK Trianguli Australis have their unique characteristics, including planets and variable brightness.
• Other features: ESO 69-6 is a pair of galaxies that are colliding and merging, located about 600 million light years from the solar system. NGC 6025 is an open cluster with an apparent magnitude of 5.1, approximately 2,700 light years away and discovered by Nicolas Louis de Lacaille in 1751-1752. NGC 5938 is a spiral galaxy around 300 million light years from Earth, south of Epsilon Trianguli Australis. The Jellyfish Galaxy (ESO 137-001) is a barred spiral galaxy in the Norma Cluster, notable for its 260,000 light-year tail. NGC 5979 is a planetary nebula with an apparent magnitude of 12.3. Henize 2-138 is a smaller planetary nebula with a visual magnitude of 11.0.
• Mythology: Triangulum Australe is the smallest of the 12 constellations created by Dutch navigators in the late 16th century and has no associated myths. It first appeared in 1589 on a celestial globe by Petrus Plancius, where it was incorrectly labeled Triangulus Antarcticus. Johann Bayer named it Triangulum Australe in 1603. In 1756, Nicolas Louis de Lacaille referred to it as “le Triangle Austral ou le Niveau,” relating it to surveying tools. Johann Bode later called it Libella in 1801.
• Visibility: Triangulum Australe is the 83^rd largest constellation, covering 110 square degrees. It is situated in the third quadrant of the southern hemisphere (SQ3) and is visible at latitudes ranging from +25° to -90°. The constellations that border it include Apus, Ara, Circinus, and Norma. The name Triangulum Australe is pronounced /traɪˈæŋɡjʊləm ɔːˈstræliː/. In English, it is referred to as the Southern Triangle. The genitive form used for star names is Trianguli Australis (pronunciation: /traɪˈæŋɡjʊlaɪ ɔːˈstrælɪs/). The three-letter abbreviation, which was established by the International Astronomical Union (IAU) in 1922, is TrA. Triangulum Australe is part of the Hercules family of constellations, which also includes Aquila, Ara, Centaurus, Corona Australis, Corvus, Crater, Crux, Cygnus, Hercules, Hydra, Lupus, Lyra, Ophiuchus, Sagitta, Scutum, Sextans, Serpens, and Vulpecula.

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Constellations:

Triangulum Australe courtesy of Openverse

Constellations of the Month:
July – Triangulum Australe

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