Editing Triangulum (section)

==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"/>

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