View source for Triangulum

{{Short description|Constellation in the northern celestial hemisphere}}
{{Other uses}}
{{Featured article}}
{{Infobox constellation
| name = Triangulum
| abbreviation = Tri
| genitive = Trianguli
| pronounce = {{IPAc-en|t|r|aɪ|ˈ|æ|ŋ|ɡ|j|ʊ|l|ə|m}},<br />genitive {{IPAc-en|t|r|aɪ|ˈ|æ|ŋ|ɡ|j|ʊ|l|aɪ}}
| symbolism = The [[Triangle]]
| RA = {{RA|01|31.3}} to {{RA|02|50.4}}<ref name=boundary/>
| dec= 25.60° to 37.35°<ref name=boundary/>
| family = [[Perseus Family|Perseus]]
| quadrant = NQ1
| areatotal = 132
| arearank = 78th
| numbermainstars = 3
| numberbfstars = 14
| numberbrightstars = 0
| numbernearbystars = 0
| brighteststarname = [[Beta Trianguli|β Tri (Alaybasan)]]
| starmagnitude = 3.00
| neareststarname = [[GJ 3147]]
| stardistancely = 35.29
| stardistancepc = 10.82
| numbermessierobjects = 1
| bordering = [[Andromeda (constellation)|Andromeda]]<br />[[Pisces (constellation)|Pisces]]<br />[[Aries (constellation)|Aries]]<br />[[Perseus (constellation)|Perseus]]
| latmax = [[North Pole|90]]
| latmin = [[53rd parallel south|53]]
| month = December
| notes=
}}
{{Contains special characters|cuneiform}}

'''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 designation]]s.

The white stars [[Beta Trianguli|Beta]] and [[Gamma Trianguli]], of [[apparent magnitude]]s 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 system]]s with known [[exoplanet|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 {{Transliteration|sux|<sup>MUL</sup>APIN}} ({{lang|sux|{{cuneiform|8|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&nbsp;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]].<ref>{{cite journal| author=Rogers, John H. |title= Origins of the Ancient Constellations: I. The Mesopotamian Traditions  |journal=Journal of the British Astronomical Association |volume=108 |date=1998|pages= 9–28|bibcode = 1998JBAA..108....9R }}</ref>

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 [[Latin]]ised as Deltotum.<ref name=allen>{{cite book  | last=Allen  | first=Richard Hinckley  | date=1963  | orig-year=1899  | author-link=Richard Hinckley Allen  | title=[[Star Names: Their Lore and Meaning]]  | edition=Reprint  | publisher=Dover Publications Inc.  | location=New York, New York  | isbn=((0-486-21079-0)) | pages=[https://archive.org/details/starnamestheirlo00alle/page/414 414–15]  }}</ref> [[Eratosthenes]] linked it with the [[Nile Delta]], while the Roman writer [[Gaius Julius Hyginus|Hyginus]] associated it with the triangular island of [[Sicily]], formerly known as Trinacria due to its shape.<ref name=ridpathtri>{{cite web| url=http://www.ianridpath.com/startales/triangulum.html | title=Triangulum |author=Ian Ridpath |author-link=Ian Ridpath|publisher=self-published | access-date= August 29, 2013}}</ref><!-- cites two previous sentences --> It was also called ''Sicilia'', because the Romans believed [[Ceres (Roman mythology)|Ceres]], patron goddess of Sicily, begged [[Jupiter (mythology)|Jupiter]] to place the island in the heavens.<ref name=allen /> 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.<ref name=allen /> [[Alpha Trianguli|Alpha]] and [[Beta Trianguli]] were called ''Al Mīzān'', which is [[Arabic language|Arabic]] for "The Scale Beam".<ref name=garfinckle1997/> 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.<ref name=ridpathtri/><ref>{{cite book  | last = Olcott  | first = William Tyler  | date = 2004 | orig-year = 1911|pages=22–23 | title = Star Lore: Myths, Legends, and Facts  | publisher = Courier Dover Publications|location=Mineola, New York  | isbn = 978-0-486-43581-7}}</ref>

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.<ref name=allen /> Polish astronomer [[Johannes Hevelius]] excised three faint stars—[[Iota Trianguli|ι]], [[10 Trianguli|10]] and [[12 Trianguli]]—to form the new constellation of [[Triangulum Minus]] in his 1690 ''Firmamentum Sobiescianum'', renaming the original as Triangulum Majus.<ref>{{cite web| url=http://www.ianridpath.com/startales/triangulumminus.html | title=Triangulum Minus |author=Ian Ridpath |author-link=Ian Ridpath|publisher=self-published | access-date= August 29, 2013}}</ref> The smaller constellation was not recognised by the [[International Astronomical Union]] (IAU) when the constellations were [[Constellation#IAU constellations|established in the 1920s]].<ref name=garfinckle1997>{{cite book | first1=Robert A. | last1=Garfinkle | title=Star-Hopping: Your Visa to Viewing the Universe | publisher=Cambridge University Press |location=Cambridge, United Kingdom |date=1997 | isbn=0-521-59889-3 | page=238 | url=https://books.google.com/books?id=40JzBYGREL0C&pg=PA238 }}</ref>

==Characteristics==
A small constellation, Triangulum is bordered by Andromeda to the north and west, [[Pisces (constellation)|Pisces]] to the west and south, [[Aries (constellation)|Aries]] to the south, and [[Perseus (constellation)|Perseus]] to the east. The centre of the constellation lies halfway between Gamma Andromedae and [[Alpha Arietis]].<ref>{{cite book|last=Simpson|first=L. Phil|title=Guidebook to the Constellations: Telescopic Sights, Tales, and Myths|publisher=Springer|location=New York, New York|date=2012|page=417|isbn=978-1-4419-6941-5|url=https://books.google.com/books?id=7gde2t9ta4QC&q=delta+triangulum&pg=PA417}}</ref> The three-letter abbreviation for the constellation, as adopted by the IAU in 1922, is "Tri".<ref name=pa30_469>{{cite journal | last=Russell | first=Henry Norris |author-link=Henry Norris Russell | title=The New International Symbols for the Constellations | journal=[[Popular Astronomy (US magazine)|Popular Astronomy]] | volume=30 | pages=469–71 | bibcode=1922PA.....30..469R | date=1922 }}</ref> The official constellation boundaries, as set by Belgian astronomer [[Eugène Joseph Delporte|Eugène Delporte]] in 1930, are defined as a polygon of 14 segments. In the [[equatorial coordinate system]], the [[right ascension]] coordinates of these borders lie between {{RA|01|31.3}} and {{RA|02|50.4}}, while the [[declination]] coordinates are between 25.60° and 37.35°.<ref name=boundary>{{Cite web | title=Triangulum, Constellation Boundary | work=The Constellations | publisher=International Astronomical Union | url=https://www.iau.org/public/themes/constellations/#tri | access-date=24 May 2013}}</ref>  Covering 132 square degrees and 0.320% of the night sky, Triangulum ranks 78th of the 88 constellations in size.<ref name=bagnall>{{cite book |last=Bagnall |first=Philip M. |title=The Star Atlas Companion: What You Need to Know about the Constellations |publisher=Springer  |location=New York, New York |date=2012 |isbn=978-1-4614-0830-7 |page=436 |url=https://books.google.com/books?id=KcIg02TKW6QC&pg=PA436}}</ref>

==Features==
{{see also|List of stars in Triangulum}}
Bayer catalogued five stars in the constellation, giving them the [[Bayer designation]]s 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.<ref name=wagman>{{cite book  | last = Wagman  | first = Morton  | date = 2003  | title = Lost Stars: Lost, Missing and Troublesome Stars from the Catalogues of Johannes Bayer, Nicholas Louis de Lacaille, John Flamsteed, and Sundry Others  | publisher = The McDonald & Woodward Publishing Company  | location = Blacksburg, Virginia  | isbn = 978-0-939923-78-6 |pages=301–02, 348}}</ref> Flamsteed gave 16 stars [[Flamsteed designation]]s, 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 his ''Catalogus Britannicus''; Baily presumed that the coordinates were mistranscribed 32<sup>[[Right ascension#Explanation|s]]</sup> 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.<ref name=wagman/>

[[Image:TriangulumCC.jpg|thumb|left|256px|The constellation Triangulum as it can be seen by the naked eye.]]

===Stars===
Three stars make up the long narrow triangle that gives the constellation its name. The brightest member is the white [[giant star]] Beta Trianguli of [[apparent magnitude]] 3.00,<ref name=garfinckle1997/> lying 127 [[light-year]]s distant from Earth.<ref>{{cite web |url = http://simbad.u-strasbg.fr/simbad/sim-id?Ident=Beta+trianguli&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id |title = Beta Trianguli |work = SIMBAD Astronomical Database|publisher=Centre de Données astronomiques de Strasbourg |access-date = 29 August 2013}}</ref> It is actually a [[spectroscopic 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-white [[F-type main-sequence star]] around 1.4 solar masses. The two orbit around a common [[Center of mass|centre of gravity]] every 31 days, and are surrounded by a [[debris disk|ring of dust]] that extends from 50 to 400&nbsp;[[Astronomical unit|AU]] away from the stars.<ref>{{cite journal|author =Kennedy, G. M.|author2 =Wyatt, M. C.|author3 = Sibthorpe, B.|author4 = Phillips, N. M.|author5 = Matthews, B.|author6 = Greaves, J. S.|date=2012|title=Coplanar Circumbinary Debris Disks|journal=[[Monthly Notices of the Royal Astronomical Society]]|volume=426|issue=3|pages=2115–28|bibcode=2012MNRAS.426.2115K|doi=10.1111/j.1365-2966.2012.21865.x|doi-access =free|arxiv = 1208.1759 |s2cid =59408005}}</ref>

The second-brightest star, the yellow-white [[subgiant]] star Alpha Trianguli (3.41<sup>m</sup>) with a close dimmer companion, is also known as Caput Trianguli or Ras al Muthallath, and is at the apex of the [[triangle]]. It lies around 7 degrees north-northwest of [[Alpha Arietis]].<ref name="motz">{{cite book |last1=Motz |first1=Lloyd |author-link1=Lloyd Motz |last2=Nathanson |first2=Carol |title=The Constellations: An Enthusiast's Guide to the Night Sky |publisher=Aurum Press |location=London, United Kingdom |date=1991 |pages=310–12 |isbn=1-85410-088-2}}</ref> Making up the triangle is [[Gamma Trianguli]], a [[A-type main sequence star|white main sequence star]] of spectral type A1Vnn of apparent magnitude 4.00 about 112 light-years from Earth.<ref name=sb1>{{cite web |url=http://simbad.u-strasbg.fr/simbad/sim-id?Ident=Gamma+Trianguli&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id |title=Gamma Trianguli |work=[[SIMBAD|SIMBAD Astronomical Database]] |publisher=Centre de Données astronomiques de Strasbourg |access-date=25 May 2013}}</ref> 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.<ref name=apj660_2_1556>{{citation | last1=Rhee | first1=Joseph H. | last2=Song | first2=Inseok | last3=Zuckerman | first3=B. | last4=McElwain | first4=Michael | title=Characterization of Dusty Debris Disks: The IRAS and Hipparcos Catalogs | journal=The Astrophysical Journal | volume=660 | issue=2 | pages=1556–71 |date=May 2007 | doi=10.1086/509912 | bibcode=2007ApJ...660.1556R |arxiv = astro-ph/0609555 | s2cid=11879505 }}</ref> Lying near Gamma and forming an optical triple system with it are [[Delta Trianguli|Delta]] and [[7 Trianguli]]. Delta is a [[binary star#Spectroscopic binaries|spectroscopic binary]] system composed of two [[G-type main-sequence star|yellow 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.<ref name=kalerdeltatri>{{cite web |url=http://stars.astro.illinois.edu/sow/deltatri.html |title=Delta Trianguli |last=Kaler |first=Jim |author-link=Jim Kaler |work=Stars |publisher=University of Illinois |access-date=16 June 2013}}</ref> This system is the closest in the constellation to the Earth.<ref name=bagnall/> Only of magnitude 5.25, 7 Trianguli is much further away at around 280 light-years distant from Earth.<ref>{{cite web |url = http://simbad.u-strasbg.fr/simbad/sim-id?Ident=7+Trianguli&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id |title = 7 Trianguli |work = SIMBAD Astronomical Database|publisher=Centre de Données astronomiques de Strasbourg |access-date = 29 August 2013}}</ref>

[[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.<ref>{{cite book|author=Burnham, Robert Jr. |date=1978 |title=Burnham's Celestial Handbook |url=https://archive.org/details/burnhamscelestia02robe |url-access=registration |publisher= Dover Publications |location=New York, New York |isbn= 0-486-24065-7}}</ref> [[X Trianguli]] is an [[binary star#Eclipsing binaries|eclipsing binary]] system that ranges between magnitudes 8.5 and 11.2 over a period of 0.97 days.<ref name="levy05">{{cite book|last=Levy|first=David H.|title=David Levy's Guide to Variable Stars|publisher=Cambridge University Press|location=Cambridge, United Kingdom|date=2005|page=227|isbn=0-521-60860-0|url=https://books.google.com/books?id=Df9d8FBagqEC&q=%22X+trianguli%22&pg=PA227}}</ref> [[RW Trianguli]] is a [[cataclysmic variable star]] system composed of a [[white dwarf]] primary and an [[K-type main-sequence star|orange main sequence star]] of spectral type K7 V. The former is drawing off matter from the latter, forming a prominent [[accretion disc]]. The system is around 1076 light-years distant.<ref>{{cite journal|author =Groot, Paul J.|author2 =Rutten, Rene G.M.|author3 =van Paradijs, Jan  |date=2004|title=A Spectrophotometric Study of RW Trianguli|journal=Astronomy & Astrophysics|volume=417|pages=283–91| doi=10.1051/0004-6361:20031771|arxiv = astro-ph/0401029 |bibcode = 2004A&A...417..283G |s2cid =15078798}}</ref>

[[R Trianguli]] is a [[Mira variable|long period (Mira) variable]] that ranges from magnitude 6.2 to 11.7 over a period of 267 days.<ref name="levy05"/> It is a [[red giant]] of spectral type M3.5-8e, lying around 960 light-years away.<ref>{{cite web |url =http://simbad.u-strasbg.fr/simbad/sim-id?Ident=R+Tri&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id |title = R Trianguli – Variable Star of Mira Ceti type |work = SIMBAD Astronomical Database|publisher=Centre de Données astronomiques de Strasbourg |access-date = 21 July 2013}}</ref> [[HD 12545]], also known as XX Trianguli, is
an orange giant of spectral type K0III around 520 light-years distant with a visual magnitude of 8.42.<ref name=sbxx>{{cite web |url=http://simbad.u-strasbg.fr/simbad/sim-id?Ident=HD+12545&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id |title=XX Trianguli – Variable of RS CVn type |work=[[SIMBAD|SIMBAD Astronomical Database]] |publisher=Centre de Données astronomiques de Strasbourg |access-date=26 July 2013}}</ref> A huge [[starspot]] larger than the diameter of the Sun was detected on its surface in 1999 by astronomers using [[Doppler imaging]].<ref>{{cite journal|bibcode=1999A&A...347..225S|title=Doppler imaging of stellar surface structure. XI. The super starspots on the K0 giant HD 12545: Larger than the entire Sun|journal=Astronomy and Astrophysics|volume=347|pages=225|last1=Strassmeier|first1=K. G|year=1999}}</ref>

Two [[star system]]s appear to have [[exoplanet|planets]]. [[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 of [[Jupiter]], with orbital periods of 30 and 193 days respectively.<ref name=aaa513>{{cite journal |doi=10.1051/0004-6361/200913790 |last1=Hébrard |first1=Guillaume |last2=Bonfils |first2=Xavier |last3=Ségransan |first3=Damien |last4=Moutou |first4=Claire |last5=Delfosse |first5=Xavier |last6=Bouchy |first6=François |last7=Boisse |first7=Isabelle |last8=Arnold |first8=Luc |date=2010 |title=The SOPHIE Search for Northern Extrasolar Planets: II. A Multi-planet System Around HD 9446 |journal=Astronomy & Astrophysics |volume=513 |pages=A69 |url=http://www.aanda.org/articles/aa/full_html/2010/05/aa13790-09/aa13790-09.html |bibcode=2010A&A...513A..69H |arxiv=1001.0682 |s2cid=119306916 }}</ref> [[HD 13189]] is an orange giant of spectral type K2II about 2–7 times as massive as the Sun with a planetary or [[brown 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.<ref name=aaa437_2_743>{{cite journal  | last1=Hatzes | first1=A. P. | last2=Guenther | first2=E. W. | last3=Endl | first3=M. | last4=Cochran | first4=W. D. | last5=Döllinger | first5=M. P. | last6=Bedalov | first6=A. | title=A giant planet around the massive giant star HD 13189 | journal=[[Astronomy and Astrophysics]] | date=2005 | volume=437 | issue=2 | pages=743–51 | doi=10.1051/0004-6361:20052850 | bibcode=2005A&A...437..743H| url=http://www.aanda.org/articles/aa/pdf/2005/26/aa2850-05.pdf | doi-access=free }}</ref><!-- cites previous two sentences -->

===Deep-sky objects===
[[File:The peculiar asymmetry of NGC 949.jpg|thumb|The peculiar asymmetry of [[NGC 949]].<ref>{{cite web|title=The peculiar asymmetry of NGC 949|url=http://www.spacetelescope.org/images/potw1518a/|access-date=14 June 2015}}</ref>]]

The [[Triangulum Galaxy]], also known as Messier 33, was discovered by [[Giovanni Battista Hodierna]] in the 17th century.<ref name=jha16_1>{{cite journal | first1=G.|first2=L.|first3= P. | title=Hodierna's Observations of Nebulae and his Cosmology | journal=Journal for the History of Astronomy | volume=16 | issue=1 |date=February 1985 | pages=1–36 | bibcode=1985JHA....16....1F | last2=Indorato | last3=Nastasi | last1=Fodera-Serio |doi=10.1177/002182868501600101|s2cid=118328541| doi-access=free }}</ref> A distant member of the [[Local 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 under [[Light pollution|light-polluted]] skies, even with a small telescope or binoculars, and low power is required to view it. It is a [[spiral galaxy]] with a diameter of 46,000 light-years and is thus smaller than both the [[Andromeda Galaxy]] and the [[Milky Way]]. A distance of less than 300 [[parsec|kiloparsecs]] between it and Andromeda supports the hypothesis that it is a satellite of the larger galaxy.<ref name="pawlowski">{{cite journal|author=Pawlowski, Marcel S.|author2=Kroupa, Pavel|author3=Jerjen, Helmut |date=2013|title=Dwarf Galaxy Planes: the Discovery of Symmetric Structures in the Local Group|journal=Monthly Notices of the Royal Astronomical Society|volume=435|issue=3|pages=1928|arxiv=1307.6210|doi=10.1093/mnras/stt1384|doi-access=free |bibcode = 2013MNRAS.435.1928P |s2cid=53991672}}</ref> It is believed to have been interacting with it from their velocities.<ref name=science307_5714>{{cite journal | author=Brunthaler, Andreas | display-authors=4 | author2=Reid, Mark J. | author3=Falcke, Heino | author4=Greenhill, Lincoln J.| author5=Henkel, Christian | date=2005 | title=The Geometric Distance and Proper Motion of the Triangulum Galaxy (M33) | journal=Science | volume=307 | issue=5714 | pages=1440–1443 | bibcode=2005Sci...307.1440B | doi=10.1126/science.1108342 | pmid=15746420|arxiv = astro-ph/0503058 | s2cid=28172780 }}</ref> Within the constellation, it lies near the border of Pisces, 3.5 degrees west-northwest of Alpha Trianguli and 7 degrees southwest of [[Beta Andromedae]].<ref name="motz"/> Within the galaxy, [[NGC 604]] is an [[H II region]] where star formation takes place.<ref>{{Cite APOD|title=NGC 604: Giant Stellar Nursery in M33 |date=16 August 1996 |access-date=8 September 2013}}</ref><ref name="hoetal1997">{{Cite journal | last1 = Ho | first1 = Luis C. | last2 = Filippenko | first2 = Alexei V. | last3 = Sargent | first3 = Wallace L. W. | date = October 1997 | title = A Search for "Dwarf" Seyfert Nuclei. III. Spectroscopic Parameters and Properties of the Host Galaxies| journal = Astrophysical Journal Supplement| volume = 112| pages = 315–390| bibcode = 1997ApJS..112..315H| doi = 10.1086/313041| issue = 2 |arxiv = astro-ph/9704107 | s2cid = 17086638}}</ref>

[[File:A distorted duo IC 1727 UGC 1249.jpg|left|thumb|[[IC 1727]] and [[UGC 1249]].<ref>{{cite web|title=A distorted duo|url=https://www.spacetelescope.org/images/potw1733a/|website=www.spacetelescope.org|access-date=14 August 2017}}</ref>]]

In addition to M33, there are several NGC galaxies of visual magnitudes 12 to 14.<ref name=garfinckle1997/> The largest of these include the 10 [[minute of arc|arcminute]] long magnitude 12 [[NGC 925]] spiral galaxy and the 5 arcminute long magnitude 11.6 [[NGC 672]] barred spiral galaxy. The latter is close by and appears to be interacting with [[IC 1727]]. The two are 88,000 light-years apart and lie around 18 million light-years away.<ref>{{cite web|url=http://www.noao.edu/outreach/aop/observers/n672.html|title=NGC 672|last=Block|first=Adam|date=20 October 2003|publisher=National Optical Astronomy Observatory|access-date=8 September 2013|archive-date=24 May 2015|archive-url=https://web.archive.org/web/20150524081149/http://www.noao.edu/outreach/aop/observers/n672.html|url-status=dead}}</ref> 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 spiral [[NGC 784]]. Together with two isolated dwarf galaxies, these fourteen appear to be moving in a common direction and constitute a group possibly located on a [[dark matter]] [[Galaxy filament|filament]].<ref>{{cite journal|author =Zitrin, Adi|author2 =Brosch, Noah |date=2008|title=The NGC 672 and 784 galaxy groups: evidence for galaxy formation and growth along a nearby dark matter filament|journal=Monthly Notices of the Royal Astronomical Society |volume=390|issue=1|pages=408–20|doi=10.1111/j.1365-2966.2008.13786.x|doi-access =free |arxiv = 0808.1789 |bibcode = 2008MNRAS.390..408Z |s2cid =16296617 }}</ref> [[3C 48]] was the first [[quasar]] ever to be observed, although its true identity was not uncovered until after that of [[3C 273]] in 1963.<ref>{{cite book|last=Robertson|first=Peter |title=Beyond Southern Skies: Radio Astronomy and the Parkes Telescope|publisher=Cambridge University Press|location=Cambridge, United Kingdom| date=1992|page=234|isbn=0-521-41408-3|url=https://books.google.com/books?id=OBOY2G_3BCgC&q=3C+48&pg=PA234}}</ref> It has an apparent magnitude of 16.2 and is located about 5 degrees northwest of Alpha Trianguli.<ref name="motz"/>

{{Clear}}

==See also==
* [[Triangulum (Chinese astronomy)]]

==References==
{{reflist}}

{{Commons}}

== External links ==
* [http://www.allthesky.com/constellations/aries/ The Deep Photographic Guide to the Constellations: Triangulum]
* [http://astrojan.nhely.hu/triang.htm The clickable Triangulum]
* [https://iconographic.warburg.sas.ac.uk/category/vpc-taxonomy-017058 Warburg Institute Iconographic Database (ca 160 medieval and early modern images of Triangulum)]

{{Stars of Triangulum}}
{{Constellations}}
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[[Category:Triangulum| ]]
[[Category:Constellations]]
[[Category:Northern constellations]]
[[Category:Constellations listed by Ptolemy]]