Triangulum is a smallconstellation in the northern sky. Its name isLatin 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 astronomerPtolemy. The celestial cartographersJohann Bayer andJohn Flamsteed catalogued the constellation's stars, giving six of themBayer designations.
The white starsBeta andGamma Trianguli, ofapparent magnitudes 3.00 and 4.00, respectively, form the base of the triangle and the yellow-whiteAlpha Trianguli, of magnitude 3.41, the apex.Iota Trianguli is a notable double star system, and there are threestar systems with knownplanets located in Triangulum. The constellation contains several galaxies, the brightest and nearest of which is theTriangulum Galaxy or Messier 33—a member of theLocal Group. The firstquasar ever observed,3C 48, also lies within the boundaries of Triangulum.
In theBabylonian star catalogues, Triangulum, together withGamma Andromedae, formed the constellation known asMULAPIN (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, theMUL.APIN. The Plough was the first constellation of the "Way ofEnlil"—that is, the northernmost quarter of the Sun's path, which corresponds to the 45 days on either side ofsummer solstice. Its first appearance in the pre-dawn sky (heliacal rising) in February marked the time to begin spring ploughing inMesopotamia.[2]
The Ancient Greeks called TriangulumDeltoton (Δελτωτόν), as the constellation resembled an upper-case Greek letter delta (Δ). It was transliterated by Roman writers, then laterLatinised as Deltotum.[3]Eratosthenes linked it with theNile Delta, while the Roman writerHyginus associated it with the triangular island ofSicily, formerly known as Trinacria due to its shape.[4] It was also calledSicilia, because the Romans believedCeres, patron goddess of Sicily, beggedJupiter to place the island in the heavens.[3] Greek astronomers such as Hipparchos and Ptolemy called itTrigonon (Τρίγωνον), and later, it was Romanized as Trigonum. Other names referring to its shape include Tricuspis and Triquetrum.[3]Alpha andBeta Trianguli were calledAl Mīzān, which isArabic for "The Scale Beam".[5] In Chinese astronomy, Gamma Andromedae and neighbouring stars including Beta, Gamma and Delta Trianguli were calledTeen 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 cartographerJohann 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 fromTriangulum Australe, the Southern Triangle.[3] Polish astronomerJohannes Hevelius excised three faint stars—ι,10 and12 Trianguli—to form the new constellation ofTriangulum Minus in his 1690Firmamentum Sobiescianum, renaming the original as Triangulum Majus.[7] The smaller constellation was not recognised by theInternational Astronomical Union (IAU) when the constellations wereestablished in the 1920s.[5]
A small constellation, Triangulum is bordered by Andromeda to the north and west,Pisces to the west and south,Aries to the south, andPerseus to the east. The centre of the constellation lies halfway between Gamma Andromedae andAlpha Arietis.[8] The three-letter abbreviation for the constellation, as adopted by the IAU in 1922, is "Tri".[9] The official constellation boundaries, as set by Belgian astronomerEugène Delporte in 1930, are defined as a polygon of 14 segments. In theequatorial coordinate system, theright ascension coordinates of these borders lie between01h 31.3m and02h 50.4m, while thedeclination coordinates are between 25.60° and 37.35°.[1] Covering 132 square degrees and 0.320% of the night sky, Triangulum ranks 78th of the 88 constellations in size.[10]
Bayer catalogued five stars in the constellation, giving them theBayer designations Alpha to Epsilon.John Flamsteed added Eta, Iota and four Roman letters; of these, only Iota is still used as the others were dropped in subsequent catalogues and star charts.[11] Flamsteed gave 16 starsFlamsteed designations, of which numbers 1 and 16 are not used—1's coordinates were in error as there was no star present at the location that corresponds to any star in hisCatalogus Britannicus; Baily presumed that the coordinates were mistranscribed 32s in error by Flamsteed and in fact referred to 7.4 magnitude HD 10407. Baily also noted that 16 Trianguli was closer to Aries and included it in the latter constellation.[11]
The constellation Triangulum as it can be seen by the naked eye.
Three stars make up the long narrow triangle that gives the constellation its name. The brightest member is the whitegiant star Beta Trianguli ofapparent magnitude 3.00,[5] lying 127light-years distant from Earth.[12] It is actually aspectroscopic binary system; the primary is a white star of spectral type A5IV with 3.5 times the mass of the Sun that is beginning to expand and evolve off the main sequence. The secondary is poorly known, but calculated to be a yellow-whiteF-type main-sequence star around 1.4 solar masses. The two orbit around a commoncentre of gravity every 31 days, and are surrounded by aring of dust that extends from 50 to 400 AU away from the stars.[13]
The second-brightest star, the yellow-whitesubgiant star Alpha Trianguli (3.41m) with a close dimmer companion, is also known as Caput Trianguli or Ras al Muthallath, and is at the apex of thetriangle. It lies around 7 degrees north-northwest ofAlpha Arietis.[14] Making up the triangle isGamma Trianguli, awhite main sequence star of spectral type A1Vnn of apparent magnitude 4.00 about 112 light-years from Earth.[15] It is around double the size of and around 33 times as luminous as the sun and rotates rapidly. Like Beta, it is surrounded by a dusty debris disk, which has a radius 80 times the distance of the Earth from the Sun.[16] Lying near Gamma and forming an optical triple system with it areDelta and7 Trianguli. Delta is aspectroscopic binary system composed of twoyellow main sequence stars of similar dimensions to the Sun that lies 35 light-years from Earth. The two stars orbit each other every ten days and are a mere 0.1 AU apart.[17] This system is the closest in the constellation to the Earth.[10] Only of magnitude 5.25, 7 Trianguli is much further away at around 280 light-years distant from Earth.[18]
Iota Trianguli is a double star whose components can be separated by medium-sized telescopes into a strong yellow and a contrasting pale blue star. Both of these are themselves close binaries.[19]X Trianguli is aneclipsing binary system that ranges between magnitudes 8.5 and 11.2 over a period of 0.97 days.[20]RW Trianguli is acataclysmic variable star system composed of awhite dwarf primary and anorange main sequence star of spectral type K7 V. The former is drawing off matter from the latter, forming a prominentaccretion disc. The system is around 1076 light-years distant.[21]
R Trianguli is along period (Mira) variable that ranges from magnitude 6.2 to 11.7 over a period of 267 days.[20] It is ared giant of spectral type M3.5-8e, lying around 960 light-years away.[22]HD 12545, also known as XX Trianguli, isan orange giant of spectral type K0III around 520 light-years distant with a visual magnitude of 8.42.[23] A hugestarspot larger than the diameter of the Sun was detected on its surface in 1999 by astronomers usingDoppler imaging.[24]
Twostar systems appear to haveplanets.HD 9446 is a Sun-like star around 171 light-years distant that has two planets of masses 0.7 and 1.8 times that ofJupiter, with orbital periods of 30 and 193 days respectively.[25]HD 13189 is an orange giant of spectral type K2II about 2–7 times as massive as the Sun with a planetary orbrown dwarf companion between 8 and 20 times as massive as Jupiter, which takes 472 days to complete an orbit. It is one of the largest stars discovered to have a planetary companion.[26]
TheTriangulum Galaxy, also known as Messier 33, was discovered byGiovanni Battista Hodierna in the 17th century.[28] A distant member of theLocal Group, it is about 2.3 million light-years away, and at magnitude 5.8 it is bright enough to be seen by the naked eye under dark skies. Being a diffuse object, it is challenging to see underlight-polluted skies, even with a small telescope or binoculars, and low power is required to view it. It is aspiral galaxy with a diameter of 46,000 light-years and is thus smaller than both theAndromeda Galaxy and theMilky Way. A distance of less than 300kiloparsecs between it and Andromeda supports the hypothesis that it is a satellite of the larger galaxy.[29] It is believed to have been interacting with it from their velocities.[30] Within the constellation, it lies near the border of Pisces, 3.5 degrees west-northwest of Alpha Trianguli and 7 degrees southwest ofBeta Andromedae.[14] Within the galaxy,NGC 604 is anH II region where star formation takes place.[31][32]
In addition to M33, there are several NGC galaxies of visual magnitudes 12 to 14.[5] The largest of these include the 10arcminute long magnitude 12NGC 925 spiral galaxy and the 5 arcminute long magnitude 11.6NGC 672 barred spiral galaxy. The latter is close by and appears to be interacting withIC 1727. The two are 88,000 light-years apart and lie around 18 million light-years away.[34] These two plus another four nearby dwarf irregular galaxies constitute the NGC 672 group, and all six appear to have had a burst of star formation in the last ten million years. The group is thought connected to another group of six galaxies known as the NGC 784 group, named for its principal galaxy, the barred spiralNGC 784. Together with two isolated dwarf galaxies, these fourteen appear to be moving in a common direction and constitute a group possibly located on adark matterfilament.[35]3C 48 was the firstquasar ever to be observed, although its true identity was not uncovered until after that of3C 273 in 1963.[36] It has an apparent magnitude of 16.2 and is located about 5 degrees northwest of Alpha Trianguli.[14]
^Rogers, John H. (1998). "Origins of the Ancient Constellations: I. The Mesopotamian Traditions".Journal of the British Astronomical Association.108:9–28.Bibcode:1998JBAA..108....9R.
^Olcott, William Tyler (2004) [1911].Star Lore: Myths, Legends, and Facts. Mineola, New York: Courier Dover Publications. pp. 22–23.ISBN978-0-486-43581-7.
^abWagman, Morton (2003).Lost Stars: Lost, Missing and Troublesome Stars from the Catalogues of Johannes Bayer, Nicholas Louis de Lacaille, John Flamsteed, and Sundry Others. Blacksburg, Virginia: The McDonald & Woodward Publishing Company. pp. 301–02, 348.ISBN978-0-939923-78-6.
^"Beta Trianguli".SIMBAD Astronomical Database. Centre de Données astronomiques de Strasbourg. Retrieved29 August 2013.
^abcMotz, Lloyd; Nathanson, Carol (1991).The Constellations: An Enthusiast's Guide to the Night Sky. London, United Kingdom: Aurum Press. pp. 310–12.ISBN1-85410-088-2.
^Strassmeier, K. G (1999). "Doppler imaging of stellar surface structure. XI. The super starspots on the K0 giant HD 12545: Larger than the entire Sun".Astronomy and Astrophysics.347: 225.Bibcode:1999A&A...347..225S.
^Ho, Luis C.; Filippenko, Alexei V.; Sargent, Wallace L. W. (October 1997). "A Search for "Dwarf" Seyfert Nuclei. III. Spectroscopic Parameters and Properties of the Host Galaxies".Astrophysical Journal Supplement.112 (2):315–390.arXiv:astro-ph/9704107.Bibcode:1997ApJS..112..315H.doi:10.1086/313041.S2CID17086638.
