Triangulum is a small constellation in the northern sky. Its name is Latin for "triangle", derived from its three brightest stars, which form a long and narrow triangle. Known to the ancient Babylonians and Greeks, Triangulum was one of the 48 constellations listed by the 2nd century astronomer Ptolemy. The celestial cartographers Johann Bayer and John Flamsteed catalogued the constellation's stars, giving six of them Bayer designations.
Triangulum Australe is a small constellation in the far Southern Celestial Hemisphere. Its name is Latin for "the southern triangle", which distinguishes it from Triangulum in the northern sky and is derived from the acute, almost equilateral pattern of its three brightest stars. It was first depicted on a celestial globe as Triangulus Antarcticus by Petrus Plancius in 1589, and later with more accuracy and its current name by Johann Bayer in his 1603 Uranometria. The French explorer and astronomer Nicolas Louis de Lacaille charted and gave the brighter stars their Bayer designations in 1756.
Alpha Trianguli is a spectroscopic binary star in the constellation of Triangulum. Based on parallax measurements obtained during the Hipparcos mission, it is approximately 63.3 light-years distant from the Sun. The brighter or primary component is named Mothallah.
Beta Trianguli is the Bayer designation for a binary star system in the constellation Triangulum, located about 127 light years from Earth. Although it is only a third-magnitude star, it is the brightest star in the constellation Triangulum.
Gamma Trianguli is a star in the constellation Triangulum located approximately 112 light years from Earth. It has an apparent magnitude of +4.01 and forms an optical (line-of-sight) triple with Delta Trianguli and 7 Trianguli.
Delta Trianguli, Latinized from Delta Tri, is a spectroscopic binary star system approximately 35 light-years (11 pc) away in the constellation of Triangulum. The primary star is a yellow dwarf, while the secondary star is thought to be an orange dwarf. It has an apparent magnitude of +4.87 and forms an optical (line-of-sight) triple with Gamma Trianguli and 7 Trianguli.
Alpha Trianguli Australis, officially named Atria, is the brightest star in the southern constellation of Triangulum Australe, forming an apex of a triangle with Beta Trianguli Australis and Gamma Trianguli Australis that gives the constellation its name.
Gamma Trianguli Australis, Latinized from γ Trianguli Australis, is a single, white-hued star in the southern constellation of Triangulum Australe. Along with Alpha and Beta Trianguli Australis it forms a prominent triangular asterism that gives the constellation its name. It is the third-brightest member of this constellation with an apparent visual magnitude of +2.87. Based upon parallax measurements, Gamma Trianguli Australis is located at a distance of about 184 light-years from Earth.
Epsilon Trianguli Australis, Latinized from ε Trianguli Australis, is a star in the southern circumpolar constellation of Triangulum Australe. It is visible to the naked eye with an apparent visual magnitude of +4.11. Based upon an annual parallax shift of 16.17 mas as seen from the Earth, the star is located about 340 light years from the Sun. The star is moving closer to the Sun with a radial velocity of around −15.5 km/s.
Kappa Trianguli Australis is a star in the constellation Triangulum Australe.
Iota Trianguli Australis is a binary star system in the constellation Triangulum Australe. It is visible to the naked eye with a combined apparent visual magnitude of +5.27. Based upon an annual parallax shift of 25.77 mas as seen from the Earth, it is located around 127 light years from the Sun. The system appears to be moving closer to the Sun with a radial velocity of around −6 km/s.
Eta Trianguli Australis is a solitary, blue-white hued star in the southern constellation Triangulum Australe. It is sometimes given a superscript: η1 Trianguli Australis, though it is the only star that is commonly referred to by this Bayer designation. Lacaille named a close by star as Eta as well, which was inconsistently followed by Francis Baily, who used the name for the brighter or both stars in two different publications. Despite their faintness, Gould upheld their Bayer designation as they were closer than 25 degrees to the south celestial pole. The second Eta is now designated as HD 150550.
Iota Trianguli, Latinized from ι Trianguli, is a quadruple star system in constellation of Triangulum. The pair have a combined apparent magnitude of 4.95 and are approximately 290 light years from Earth.
S Trianguli Australis is a yellow-white hued variable star in the constellation Triangulum Australe. It is a dim star near the lower limit of visibility with the naked eye, having a typical apparent visual magnitude of 6.41. Based upon an annual parallax shift of 1.08 mas, it is located 3,030 light years from the Earth.
R Trianguli Australis is a yellow-white hued variable star in the southern constellation Triangulum Australe. It is near the limit of visibility to the naked eye, having a typical apparent visual magnitude of 6.73. Based upon an annual parallax shift of 1.48 mas, it is located 2,210 light years away. R TrA is moving closer with a heliocentric radial velocity of −13 km/s.
5 Trianguli is a solitary star located in the northern constellation Triangulum. With an apparent magnitude of 6.23, it’s barely visible to the naked eye under ideal conditions. The star is located 399 light years away from the Solar System, but is drifting away with a radial velocity of 7.7 km/s.
7 Trianguli is a solitary star located in the northern constellation Triangulum. It has an apparent magnitude of 5.25, making it faintly visible to the naked eye under ideal conditions. The star is situated at distance of 360 light years but is approaching with a heliocentric radial velocity of −1.3 km/s, which is poorly constrained.
10 Trianguli is a solitary star located in the northern constellation Triangulum. It has an apparent magnitude of 5.28, making it faintly visible to the naked eye under ideal conditions. The star is situated 363 light years away and is thought to be moving further away with a heliocentric radial velocity of 0.457 km/s, although this value varies widely depending on the study.
12 Trianguli is a solitary star located in the northern constellation Triangulum, with an apparent magnitude of 5.37, making it faintly visible to the naked eye under ideal conditions. The star is situated 160 light years away but is approaching with a heliocentric radial velocity of −24.8 km/s. It is calculated to be about 2.19 Gyr old with a stellar classification of F0 III, making it an F-type giant. It has 1.6 times the mass of the Sun and shines at 14 times the luminosity of the Sun from its photosphere at an effective temperature of 7,199 K.
15 Trianguli is a suspected variable star located in the northern constellation Triangulum, with an apparent magnitude of 5.4 making it faintly visible to the naked eye under ideal conditions, although it is suspected of being an irregular variable with a range of 0.14 magnitudes. The star is situated about 480 light years away but is approaching with a heliocentric radial velocity of −8.646 km/s.
