genitive /
SymbolismThe Triangle
Right ascension 01h 31.3m to  02h 50.4m[1]
Declination25.60° to 37.35°[1]
Area132 sq. deg. (78th)
Main stars3
Stars with planets3
Stars brighter than 3.00m0
Stars within 10.00 pc (32.62 ly)0
Brightest starβ Tri (3.00m)
Messier objects1
Meteor showersNone
Visible at latitudes between +90° and −60°.
Best visible at 21:00 (9 p.m.) during the month of December.

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.

The white stars Beta and Gamma Trianguli, of apparent magnitudes 3.00 and 4.00, respectively, form the base of the triangle and the yellow-white Alpha Trianguli, of magnitude 3.41, the apex. Iota Trianguli is a notable double star system, and there are three star systems with known planets located in Triangulum. The constellation contains several galaxies, the brightest and nearest of which is the Triangulum Galaxy or Messier 33—a member of the Local Group. The first quasar ever observed, 3C 48, also lies within the boundaries of Triangulum.

History and mythology

In the Babylonian star catalogues, Triangulum, together with Gamma Andromedae, formed the constellation known as MULAPIN (𒀯𒀳) "The Plough". It is notable as the first constellation presented on (and giving its name to) a pair of tablets containing canonical star lists that were compiled around 1000 BC, the MUL.APIN. The Plough was the first constellation of the "Way of Enlil"—that is, the northernmost quarter of the Sun's path, which corresponds to the 45 days on either side of summer solstice. Its first appearance in the pre-dawn sky (heliacal rising) in February marked the time to begin spring ploughing in Mesopotamia.[2]

The Ancient Greeks called Triangulum Deltoton (Δελτωτόν), as the constellation resembled an upper-case Greek letter delta (Δ). It was transliterated by Roman writers, then later Latinised as Deltotum.[3] Eratosthenes linked it with the Nile Delta, while the Roman writer Hyginus associated it with the triangular island of Sicily, formerly known as Trinacria due to its shape.[4] It was also called Sicilia, because the Romans believed Ceres, patron goddess of Sicily, begged Jupiter to place the island in the heavens.[3] Greek astronomers such as Hipparchos and Ptolemy called it Trigonon (Τρίγωνον), and later, it was Romanized as Trigonum. Other names referring to its shape include Tricuspis and Triquetrum.[3] Alpha and Beta Trianguli were called Al Mīzān, which is Arabic for "The Scale Beam".[5] In Chinese astronomy, Gamma Andromedae and neighbouring stars including Beta, Gamma and Delta Trianguli were called Teen Ta Tseang Keun (天大将军, "Heaven's great general"), representing honour in astrology and a great general in mythology.[4][6]

Later, the 17th-century German celestial cartographer Johann Bayer called the constellation Triplicitas and Orbis terrarum tripertitus, for the three regions Europe, Asia, and Africa. Triangulus Septentrionalis was a name used to distinguish it from Triangulum Australe, the Southern Triangle.[3] Polish astronomer Johannes Hevelius excised three faint stars—6, 10 and 12 Trianguli—to form the new constellation of Triangulum Minus in his 1690 Firmamentum Sobiescianum, renaming the original as Triangulum Majus.[7] The smaller constellation was not recognised by the International Astronomical Union (IAU) when the constellations were established in the 1920s.[5]

Other Languages
asturianu: Triangulum
azərbaycanca: Üçbucaq (bürc)
Bân-lâm-gú: Saⁿ-kak-chō
беларуская (тарашкевіца)‎: Трыкутнік (сузор’е)
corsu: Triangulum
dansk: Trekanten
Ελληνικά: Τρίγωνον
español: Triangulum
فارسی: سه‌سو
Gaeilge: An Triantán
galego: Triangulum
客家語/Hak-kâ-ngî: Sâm-kok-chho
한국어: 삼각형자리
Lëtzebuergesch: Triangulum (Stärebild)
Bahasa Melayu: Segi Tiga (buruj)
Mìng-dĕ̤ng-ngṳ̄: Săng-gáe̤k-cô̤
日本語: さんかく座
norsk: Triangelet
norsk nynorsk: Triangelet
oʻzbekcha/ўзбекча: Uchburchak (yulduz turkumi)
português: Triangulum
Scots: Triangulum
Simple English: Triangulum
slovenščina: Trikotnik (ozvezdje)
српски / srpski: Троугао (сазвежђе)
srpskohrvatski / српскохрватски: Trokut (zviježđe)
Tiếng Việt: Tam Giác (chòm sao)
Winaray: Triangulum
粵語: 三角座
中文: 三角座