Editing Triangulum Australe

{{Short description|Constellation in the southern celestial hemisphere}}
{{Infobox constellation
| abbreviation = TrA
| name = Triangulum Australe
| genitive = Trianguli Australis
| pronounce = {{IPAc-en|t|r|aɪ|ˈ|æ|ŋ|ɡ|j|ʊ|l|ə|m|_|ɒ|s|ˈ|t|r|eɪ|l|iː}},<br/>genitive {{IPAc-en|t|r|aɪ|ˈ|æ|ŋ|ɡ|j|ʊ|l|aɪ|_|ɒ|ˈ|s|t|r|eɪ|l|ɪ|s}}
| symbolism = the Southern [[Triangle]]
| RA =  {{RA|14|56.4}} to {{RA|17|13.5}}{{sfn|IAU Constellation Boundary}}
| dec= −60.26° to −70.51°{{sfn|IAU Constellation Boundary}}
| family = [[Hercules Family|Hercules]]
| quadrant = SQ3
| areatotal = 110
| arearank = 83rd
| numbermainstars = 3
| numberbfstars = 10
| numberstarsplanets = 1
| numberbrightstars = 3
| numbernearbystars = 0
| brighteststarname = [[Alpha Trianguli Australis|α TrA]] (Atria)
| starmagnitude = 1.91
| neareststarname = [[Zeta Trianguli Australis|ζ TrA]]
| stardistancely = 39.48
| stardistancepc = 12.11
| numbermessierobjects = 0
| meteorshowers = 0
| bordering = [[Norma (constellation)|Norma]]<br />[[Ara (constellation)|Ara]]<br />[[Circinus]]<br />[[Apus]]
| latmax = [[25th parallel north|25]]
| latmin = [[South Pole|90]]
| month = July
| notes=
}}

'''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 triangle|acute]], almost [[equilateral triangle|equilateral pattern]] of its three brightest [[star]]s. 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 designation]]s in 1756.

[[Alpha Trianguli Australis]], known as Atria, is a [[apparent magnitude|second-magnitude]] orange [[bright giant|giant]] and the brightest star in the constellation, as well as the 42nd-brightest star in the night sky. Completing the triangle are the two [[A-type main sequence star|white main sequence]] stars [[Beta Trianguli Australis|Beta]] and [[Gamma Trianguli Australis]]. Although the constellation lies in the [[Milky Way]] and contains many stars, [[deep-sky object]]s are not prominent. Notable features include the [[open cluster]] [[NGC 6025]] and [[planetary nebula]] [[NGC 5979]].

The [[Great Attractor]], the gravitational center of the [[Laniakea Supercluster]] which includes the Milky Way galaxy, straddles Triangulum Australe and the neighboring constellation [[Norma (constellation)|Norma]].<ref>{{cite web |url=https://www.nasa.gov/mission_pages/hubble/science/great-attractor.html |title=Hubble focuses on "the Great Attractor" |publisher=[[NASA]] |date=2013-01-18 |access-date=2020-10-24 |df=dmy-all}}</ref>

==History==

Italian navigator [[Amerigo Vespucci]] explored the New World at the beginning of the 16th century. He learnt to recognize the stars in the southern hemisphere and made a catalogue for his patron king [[Manuel I of Portugal]], which is now lost. As well as the catalogue, Vespucci wrote descriptions of the southern stars, including a triangle which may be either Triangulum Australe or [[Apus]]. This was sent to his patron in Florence, [[Lorenzo di Pierfrancesco de' Medici]], and published as ''Mundus Novus'' in 1504.{{sfn|Kanas|2007|pp=118–19}} The first depiction of the constellation was provided in 1589 by Flemish astronomer and clergyman [[Petrus Plancius]] on a {{frac|32|1|2}}-cm diameter [[globe#Celestial|celestial globe]] published in Amsterdam by Dutch cartographer [[Jacob van Langren]],{{sfn|Ridpath Star Tales – Triangulum Australe}}<!-- cites previous three sentences--> where it was called Triangulus Antarcticus and incorrectly portrayed to the south of [[Argo Navis]]. His student [[Pieter Dirkszoon Keyser|Petrus Keyzer]], along with Dutch explorer [[Frederick de Houtman]], coined the name Den Zuyden Trianghel.{{sfn|Wagman|2003|pp=303–04}} Triangulum Australe was more accurately depicted in [[Johann Bayer]]'s celestial atlas ''[[Uranometria]]'' in 1603, where it was also given its current name.{{sfn|Moore|Tirion|1997|p=120}}

[[Nicolas Louis de Lacaille]] portrayed the constellations of [[Norma (constellation)|Norma]], [[Circinus (constellation)|Circinus]] and Triangulum Australe as a set square and ruler, a compass, and a surveyor's level respectively in a set of draughtsman's instruments in his 1756 map of the southern stars.{{sfn|Ridpath Star Tales – Lacaille}} Also depicting it as a surveyor's level, German [[Johann Bode]] gave it the alternate name of Libella in his ''Uranographia''.{{sfn|Ridpath Star Tales – Triangulum Australe}}

German poet and author [[Philipp von Zesen|Philippus Caesius]] saw the three main stars as representing the [[Patriarchs (Bible)|Three Patriarchs]], Abraham, Isaac and Jacob (with Atria as Abraham).{{sfn|Motz|Nathanson|1991|p=387}} The [[Wardaman people]] of the Northern Territory in Australia perceived the stars of Triangulum Australe as the tail of the [[Rainbow Serpent]], which stretched out from near [[Crux]] across to [[Scorpius]]. Overhead in October, the Rainbow Serpent "gives Lightning a nudge" to bring on the wet season rains in November.{{sfn|Harney|Cairns|2004|pp=156–57}}

==Characteristics==
[[File:Constellation Triangulum Australe.jpg|thumb|left|The constellation Triangulum Australe, the southern triangle, as it can be seen by the naked eye]]
Triangulum Australe is a small constellation bordered by Norma to the north, Circinus to the west, Apus to the south and [[Ara (constellation)|Ara]] to the east. It lies near the Pointers ([[Alpha Centauri|Alpha]] and [[Beta Centauri]]), with only Circinus in between.{{sfn|Moore|2005|p=116}} The constellation is located within the [[Milky Way]], and hence has many stars.{{sfn|Inglis|2004|p=119}} A roughly equilateral triangle, it is easily identifiable. Triangulum Australe lies too far south in the celestial southern hemisphere to be visible from Europe,{{sfn|Moore|2005|p=116}} yet is [[Circumpolar star|circumpolar]] from most of the southern hemisphere.{{sfn|Inglis|2004|p=119}} The three-letter abbreviation for the constellation, as adopted by the [[International Astronomical Union]] in 1922, is "TrA".{{sfn|Russell|1922|p=469}} The official constellation boundaries, as set by Belgian astronomer [[Eugène Joseph Delporte|Eugène Delporte]] in 1930, are defined by a polygon of 18 segments. In the [[equatorial coordinate system]], the [[right ascension]] coordinates of these borders lie between {{RA|14|56.4}} and {{RA|17|13.5}}, while the [[declination]] coordinates are between −60.26° and −70.51°.{{sfn|IAU Constellation Boundary}} Triangulum Australe [[Culmination|culminates]] each year at 9 p.m. on 23 August.{{sfn|James|2011}}

==Notable features==
{{See also|List of stars in Triangulum Australe}}

===Bright stars===
In defining the constellation, Lacaille gave twelve stars [[Bayer designation]]s of Alpha through to Lambda, with two close stars called Eta (one now known by its [[Star catalogue#HD/HDE|Henry Draper catalogue]] number), while Lambda was later dropped due to its dimness.{{sfn|Wagman|2003|pp=303–04}} The three brightest stars, Alpha, Beta and Gamma, make up the triangle. Readily identified by its orange hue,{{sfn|Moore|2005|p=116}} [[Alpha Trianguli Australis]] is a [[bright giant]] star of [[stellar classification|spectral type]] K2&nbsp;IIb-IIIa with an [[apparent magnitude]] of +1.91 that is the 42nd-brightest star in the night sky.{{sfn|Schaaf|2008|pp=263–65}} It lies {{Convert|424|ly|pc|abbr=off|lk=on}} away and has an [[absolute magnitude]] of −3.68 and is 5,500 times more luminous than the [[Sun]].{{sfn|Ayres|Brown|Harper|2007}} With a diameter 130 times that of the Sun, it would almost reach the orbit of Venus if placed at the centre of the Solar System. The proper name Atria is a contraction of its Bayer designation.{{sfn|Kaler, Atria}} [[Beta Trianguli Australis]] is a [[double star]], the primary being a  [[F-type main-sequence star]] with a stellar classification of F1V,{{sfn|Gray et al.|2006}} and an apparent magnitude of 2.85.{{sfn|Nicolet|1978}} Lying only {{Convert|40|ly|pc|abbr=off|lk=off}} away, it has an absolute magnitude of 2.38.{{sfn|Schaaf|2008|pp=263–65}} Its companion, almost 3 [[Minute and second of arc#Symbols and abbreviations|arcminutes]] away, is a 13th-magnitude star which may or may not be in orbit around Beta.{{sfn|Kaler, Beta TrA}} The remaining member of the triangle is [[Gamma Trianguli Australis]] with an apparent magnitude of 2.87.{{sfn|Wielen et al.|1999}} It is an [[A-type main sequence star]] of spectral class A1&nbsp;V, which lies {{Convert|180|ly|pc|abbr=off|lk=off}} away.{{sfn|Schaaf|2008|pp=263–65}}

Located outside the triangle near Beta, [[Delta Trianguli Australis]] is the fourth-brightest star at apparent magnitude +3.8.{{sfn|Moore|2005|p=116}} It is a yellow giant of spectral type G2Ib-II and lies {{Convert|606|ly|pc|abbr=off|lk=on}} away.{{sfn|SIMBAD Delta Trianguli Australis}} Lying halfway between Beta and Gamma, [[Epsilon Trianguli Australis]] is an optical double. The brighter star, Epsilon Trianguli Australis A, is an orange [[stellar classification|K-type]] sub-[[giant star|giant]] of spectral type K1.5III with an apparent magnitude of +4.11.{{sfn|SIMBAD Epsilon Trianguli Australis}} The optical companion, Epsilon Trianguli Australis B (or HD 138510), is a white main sequence star of spectral type A9IV/V which has an apparent magnitude of +9.32.{{sfn|SIMBAD HD 138510}} [[Zeta Trianguli Australis]] appears as a star of apparent magnitude +4.91 and spectral class F9V, but is actually a [[spectroscopic binary]] with a near companion, probably a [[red dwarf]]. The pair orbit each other once every 13 days.{{sfn|Skuljan|2004}} A young star, its proper motion indicates it is a member of the [[Ursa Major moving group]].{{sfn|Croswell|2005}} [[Iota Trianguli Australis]] shows itself to be a multiple star system composed of a yellow and a white star when seen though a 7.5&nbsp;cm telescope.{{sfn|Hartung|1984|p=214}} The brighter star has a spectral type of F4IV and is a spectroscopic binary whose components are two yellow-white stars which orbit each other every 39.88 days. The primary is a [[Gamma Doradus variable]], pulsating over a period of 1.45 days.{{sfn|De Cat et al.|2009}} The fainter star is not associated with the system, hence the system is an [[Double star|optical double]].{{sfn|Hartung|1984|p=214}} [[HD 147018]] is a Sun-like star of apparent magnitude 8.3 and spectral type G9V,{{sfn|SIMBAD LTT 6522}} which was found to have two exoplanets, [[HD 147018 b]] and [[HD 147018 c]], in 2009.{{sfn|Ségransan et al. |2010}}

Of apparent magnitude 5.11, the yellow bright giant [[Kappa Trianguli Australis]] of spectral type G5IIa lies around {{Convert|1207|ly|pc|abbr=off|lk=off}} distant from the Solar System.{{sfn|SIMBAD Kappa Trianguli Australis}} [[Eta Trianguli Australis]] (or Eta1 Trianguli Australis) is a [[Be star]] of spectral type B7IVe which is {{Convert|661|ly|pc|abbr=off|lk=off}} from Earth, with an apparent magnitude of 5.89.{{sfn|SIMBAD HR 6172}} 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, [[Benjamin Apthorp Gould|Benjamin 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.{{sfn|Wagman|2003|pp=303–04}} It is a variable star of average magnitude 6.53 and spectral type A1III.{{sfn|SIMBAD HD 150550}}

===Variable stars===
Triangulum Australe contains several [[cepheid variable]]s, all of which are too faint to be seen with the naked eye:{{sfn|Klepešta|Rükl|1974|pp=248–49}} [[R Trianguli Australis]] ranges from apparent magnitude 6.4 to 6.9 over a period of 3.389 days, [[S Trianguli Australis]] varies from magnitude 6.1 to 6.8 over 6.323 days, and [[U Trianguli Australis]]' brightness changes from 7.5 to 8.3 over 2.568 days.{{sfn|Inglis|2004|p=119}} All three are yellow-white giants of spectral type F7Ib/II,{{sfn|SIMBAD R Trianguli Australis}} F8II,{{sfn|SIMBAD S Trianguli Australis}} and F8Ib/II respectively.{{sfn|SIMBAD U Trianguli Australis}} [[RT Trianguli Australis]] is an unusual cepheid variable which shows strong [[absorption band]]s in [[molecule|molecular]] fragments of [[Diatomic carbon|C<sub>2</sub>]], [[methylidyne radical|'''⫶'''CH]] and [[cyano radical|'''⋅'''CN]], and has been classified as a carbon cepheid of spectral type R. It varies between magnitudes 9.2 and 9.97 over 1.95 days.{{sfn|Wallerstein et al. 2000}} Lying nearby Gamma, [[X Trianguli Australis]] is a variable [[carbon star]] with an average magnitude of 5.63.{{sfn|SIMBAD X Trianguli Australis}} It has two periods of around 385 and 455 days, and is of spectral type C5, 5(Nb).{{sfn|Tabur|Bedding|2009}}

[[EK Trianguli Australis]], a [[dwarf nova]] of the SU Ursae Majoris type, was first noticed in 1978 and officially described in 1980.{{sfn|Hassall|1985}} It consists of a [[white dwarf]] and a donor star which orbit each other every 1.5 hours.{{sfn|Mennickent|Arenas|1998}} The white dwarf sucks matter from the other star onto an [[accretion disc]] and periodically erupts, reaching magnitude 11.2 in [[superoutburst]]s, 12.1 in normal outbursts and remaining at magnitude 16.7 when quiet.{{sfn|Gänsicke et al.|1997}} [[NR Trianguli Australis]] was a slow nova which peaked at magnitude 8.4 in April 2008, before fading to magnitude 12.4 by September of that year.{{sfn|Bianciardi|2009}}

===Deep-sky objects===
[[File:Hubble Interacting Galaxy ESO 69-6 (2008-04-24).jpg|right|thumb|[[ESO 69-6]], two merging galaxies with prominent long tails, photographed by the [[Hubble Space Telescope]]]]
Triangulum Australe has few [[deep-sky object]]s—one open cluster and a few planetary nebulae and faint galaxies.{{sfn|Inglis|2004|p=119}} [[NGC 6025]] is an [[open cluster]] with about 30 stars ranging from 7th to 9th magnitude.{{sfn|Inglis|2004|p=119}} Located 3 degrees north and 1 east of Beta Trianguli Australis, it lies about {{Convert|2500|ly|pc|abbr=off|lk=off|sigfig=2}} away and is about {{Convert|11|ly|pc|abbr=off|lk=off|sigfig=2}}  in diameter. Its brightest star is MQ Trianguli Australis at apparent magnitude 7.1.{{sfn|Mobberley |2009|p=198}} [[NGC 5979]], a [[planetary nebula]] of apparent magnitude 12.3, has a blue-green hue at higher magnifications, while Henize 2-138 is a smaller planetary nebula of magnitude 11.0.{{sfn|Griffiths|2012|p=262}} [[NGC 5938]] is a remote [[spiral galaxy]] around 300 million light-years (90 megaparsecs) away. It is located 5 degrees south of Epsilon Trianguli Australis.{{sfn|Polakis|2001}} [[ESO 69-6]] is a pair of merging galaxies located about 600 million light-years (185 megaparsecs) away. Their contents have been dragged out in long tails by the interaction.{{sfn|Cosmic Collisions Galore!}}

==In culture==
Triangulum Australe appears on the [[flag of Brazil]], symbolizing the three states of the [[South Region, Brazil|South Region]].<ref name=brazil_flag>{{cite web | title=Astronomy of the Brazilian Flag | url=https://flagspot.net/flags/br_astro.html | publisher=FOTW Flags Of The World website | accessdate=2011-12-26 }}</ref>

[[Image:Bandeira do movimento O Sul É o Meu País.svg|thumb|The movements's flag.<ref>{{cite web|url=http://www.crwflags.com/fotw/flags/br_sep.html |title=Contemporary Separatist Movements (Brazil) |publisher=Crwflags.com |date=20 December 2008 |accessdate=2013-10-09}}</ref>]]It also appears as the only constellation used for the flag of secessionist movement [[The South Is My Country]].

==See also==
* [[IAU designated constellations|IAU-recognized constellations]]
* [[Triangulum Australe (Chinese astronomy)]]

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{{Refend}}

== External links ==
{{Commons and category|Triangulum Australe|Triangulum Australe}}
* [http://www.allthesky.com/constellations/norma/ The Deep Photographic Guide to the Constellations: Triangulum Australe]
* [http://www.starrynightphotos.com/constellations/triang_austral.htm Starry Night Photography: Triangulum Australe]

{{Sky|16|00|00|-|65|00|00|10}}

{{Stars of Triangulum Australe}}
{{Constellations}}
{{Portal bar|Astronomy|Stars|Outer space}}
{{Featured article}}

{{DEFAULTSORT:Triangulum Australe}}
[[Category:Triangulum Australe| ]]
[[Category:Southern constellations]]
[[Category:Constellations listed by Petrus Plancius]]