View source for Sextans

{{Short description|Constellation on the celestial equator}}
{{About|the constellation|the ancient Roman coin|sextans (coin)|the Sextans dwarf galaxy|Sextans Dwarf Spheroidal}}

{{Infobox constellation
| name = Sextans
| abbreviation = Sex
| genitive = Sextantis, Sextansis
| pronounce =  {{IPAc-en|ˈ|s|ɛ|k|s|t|ən|z}},<br/>genitive {{IPAc-en|s|ɛ|k|s|ˈ|t|æ|n|t|ᵻ|s}}
| symbolism = the [[sextant (astronomy)|Sextant]]
| RA = {{RA|09|41|04.8653}}–{{RA|10|51|30.2447}}{{sfn|IAU, ''The Constellations'', Sextans}}
| dec = {{dec|6.4327669}}–{{dec|-11.6621428}}{{sfn|IAU, ''The Constellations'', Sextans}}
| family = [[Hercules Family|Hercules]]
| quadrant = SQ2
| areatotal = 314
| arearank = 47th
| numbermainstars = 3
| numberbfstars = 28
| numberbrightstars = 0
| numbernearbystars = 5
| brighteststarname = [[Alpha Sextantis|α Sex]]
| starmagnitude = 4.49
| neareststarname = [[LHS 292]]
| stardistancely = 14.80
| stardistancepc = 4.54
| numbermessierobjects = 0
| meteorshowers = [[Sextantids]]
| bordering = [[Leo (constellation)|Leo]]<br />[[Hydra (constellation)|Hydra]]<br />[[Crater (constellation)|Crater]]
| latmax = [[80th parallel north|80]]
| latmin = [[90th parallel south|90]]
| month = April
| notes=
}}

'''Sextans''' is a faint, minor [[constellation]] on the [[celestial equator]] which was introduced in 1687 by [[Polish people|Polish]] astronomer [[Johannes Hevelius]]. Its name is [[Latin]] for the [[astronomical sextant]], an instrument that Hevelius made frequent use of in his observations.

==Characteristics==
Sextans is a medium sized constellation bordering [[Leo (constellation)|Leo]] to the north, touching on [[Hydra (constellation)|Hydra]] to the southwest, and [[Crater (constellation)|Crater]] to the southeast. The recommended three-letter abbreviation for the constellation, as adopted by the International Astronomical Union in 1922, is "Sex".<ref name=pa30_469>{{cite magazine | last=Russell | first=Henry Norris |author-link=Henry Norris Russell | title=The new international symbols for the constellations | magazine=[[Popular Astronomy (US magazine)|Popular Astronomy]] | volume=30 | page=469 | 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 by a square. In the [[equatorial coordinate system]], the [[right ascension]] coordinates of these borders lie between {{RA|09|41}} and {{RA|10|51}}, while the [[declination]] coordinates are between +6.43° and −11.7°.<ref name = border>{{cite web |title=International Astronomical Union {{!}} IAU |url=https://www.iau.org/public/themes/constellations/#sex |website=www.iau.org}}</ref>  Since it is close to the ecliptic plane, the Moon and planets regularly cross the constellation, especially its northeastern corner.<ref>{{Cite web |last=NOIRLab |title=Constellation: Sextans |url=https://noirlab.edu/public/education/constellations/sextans/?nocache=true& |access-date=2025-04-16 |website=www.noirlab.edu}}</ref>

==Notable features== 

=== Stars ===
{{See also|List of stars in Sextans}}
[[File:SextansCC.jpg|thumb|left|The constellation Sextans as it can be seen by the naked eye]]

[[John Flamsteed]] labeled 41 stars for the constellation.<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|VA]]  | isbn = 978-0-939923-78-6 |pages=290}}</ref> [[Francis Baily]] intended to give [[Bayer designation]]s to some of the stars but because none of them were above magnitude 4.5, he left them unlettered.<ref name="wagman"/> Rather, it was [[Benjamin Apthorp Gould]] who lettered some of the stars. He labeled the five brightest stars using [[Greek letter]]s Alpha (α) to Epsilon (ε) in his ''Uranometria Argentina''.<ref name="wagman"/> All together, there are 38 stars that are brighter than or equal to apparent magnitude 6.5.{{efn|1=Objects of magnitude 6.5 are among the faintest visible to the unaided eye in suburban–rural transition night skies.<ref>{{cite web|url=http://www.skyandtelescope.com/resources/darksky/3304011.html?page=1&c=y|title=The Bortle Dark-Sky Scale|last=Bortle|first=John E.|date=February 2001|work=[[Sky & Telescope]]|publisher=Sky Publishing Corporation|access-date=4 March 2016}}</ref>}}<ref name=tirionconst>{{cite web| url=http://www.ianridpath.com/constellations2.html | title=Constellations: Lacerta–Vulpecula | work= Star Tales |author=Ridpath, Ian|publisher=Self-published | access-date= 4 March 2016| author-link=Ian Ridpath }}</ref>

=== Bright stars ===
* [[Alpha Sextantis]] is the brightest star in the constellation and the only star above the fifth [[apparent magnitude|magnitude]] with an apparent magnitude of 4.49. It is an ageing [[A-type star]] of spectral class A0 III<ref name = Cowley1969>{{cite journal | last1 = Cowley | first1 = A. | last2 = Cowley | first2 = C. | last3 = Jaschek | first3 = M. | last4 = Jaschek | first4 = C. | title = A study of the bright stars. I. A catalogue of spectral classifications. | journal = The Astronomical Journal | date = April 1969 | volume = 74 | page = 375 | issn = 0004-6256 | doi = 10.1086/110819 | s2cid = 121555804 | bibcode = 1969AJ.....74..375C | doi-access = free}}</ref> located 280{{±|20}} [[light-year]]s away<ref name=vanLeeuwen2007>{{citation | title=Validation of the new Hipparcos reduction | last1=van Leeuwen | first1=F. | journal=Astronomy and Astrophysics | volume=474 | issue=2 | pages=653–664 | date=2007 | arxiv=0708.1752 | bibcode=2007A&A...474..653V | doi=10.1051/0004-6361:20078357 | s2cid=18759600 | postscript=. }}</ref> from the [[Solar System]]. At the age of 385 [[million years]],<ref name=Bowman>{{cite journal | doi=10.3847/1538-3881/acdee4 | doi-access=free | title=The Unexpected Optical and Ultraviolet Variability of the Standard Star α Sex (HD 87887) | date=2023 | last1=Monier | first1=Richard | last2=Bowman | first2=Dominic M. | last3=Lebreton | first3=Yveline | last4=Deal | first4=Morgan | journal=The Astronomical Journal | volume=166 | issue=2 | page=73 | arxiv=2306.08551 | bibcode=2023AJ....166...73M }}</ref> it is exhausting [[hydrogen]] at its core and leaving the [[main sequence]]. 
* [[Gamma Sextantis|γ Sextantis]] is the second brightest star in the constellation with an apparent magnitude of 5.05. It is a [[binary star]] consisting of two [[A-type main-sequence star]]s with classes of A1 V and A4 V respectively.<ref name=Edwards1976>{{citation | title=MK classification for visual binary components | last1=Edwards | first1=T. W. | journal=Astronomical Journal | postscript=. | volume=81 | pages=245–249 | date=April 1976 | doi=10.1086/111879 | bibcode=1976AJ.....81..245E }}</ref> The stars take 77.55 years to circle each other in an eccentric orbit<ref name=Heintz1982>{{citation | title=Orbits of 16 visual binaries | last1=Heintz | first1=W. D. | journal=Astronomy and Astrophysics Supplement Series | volume=47 | pages=569–573 | date=March 1982 | bibcode=1982A&AS...47..569H | postscript=. }}</ref> and the system is located 280{{±|10}} light-years away from the Solar System.<ref name=vanLeeuwen2007/> The separation of the stars is four-tenths of an [[arcsecond]],<ref name=Heintz1982/> making it difficult to observe without the use of a telescope with an aperture of 30&nbsp;cm.
* [[Beta Sextantis|β Sextantis]] is slightly fainter at magnitude 5.07;<ref name=Crawford1971>{{citation | display-authors=1 | last1=Crawford | first1=D. L. | last2=Barnes | first2=J. V. | last3=Golson | first3=J. C. | title=Four-color, H-beta, and UBV photometry for bright B-type stars in the northern hemisphere | journal=The Astronomical Journal | year=1971 | pages=1058 | volume=76 | bibcode=1971AJ.....76.1058C | doi=10.1086/111220 | postscript=. }}</ref> it is said to be 364{{±|10}} light-years distant.<ref name = GaiaDR2>{{Cite DR2|3782940437640705408}}</ref> Beta Sextantis is a [[B-type main-sequence star]] of spectral class B6 V and it has been used as a standard in the [[MK spectral classification]] system.<ref name=Mathys1986>{{citation | title=Photometric variability of some early-type stars | display-authors=1 | last1=Mathys | first1=G. | last2=Manfroid | first2=J. | last3=Renson | first3=P. | journal=Astronomy and Astrophysics Supplement Series | volume=63 | issue=3 | pages=403–416 | date=March 1986 | bibcode=1986A&AS...63..403M | postscript=. }}</ref> It is suspected to be a [[Alpha2 Canum Venaticorum variable|Alpha<sup>2</sup> Canum Venaticorum variable]] with a period of 15.4 [[days]].<ref name=Kholopov1989>{{citation | title=The 69th Name-List of Variable Stars | display-authors=1 | last1=Kholopov | first1=P. N. | last2=Samus | first2=N. N. | last3=Kazarovets | first3=B. V. | last4=Frolov | first4=M. S. | last5=Kireeva | first5=N. N. | journal=Information Bulletin on Variable Stars | issue=3323 | page=1 | date=April 1989 | volume=3323 | bibcode=1989IBVS.3323....1K | postscript=. }}</ref>

=== Multiple star systems ===
Sextans contains a few notable multiple star systems within its boundaries.

[[35 Sextantis]] is a triple star system consisting of two evolved [[K-type giant]]s of equal mass, with both stars being twice as massive as the Sun.<ref name = Tokovinin2008>{{cite journal | last=Tokovinin | first=A. | title=Comparative statistics and origin of triple and quadruple stars | journal=Monthly Notices of the Royal Astronomical Society | volume=389 | issue=2 | date= September 11, 2008 | doi=10.1111/j.1365-2966.2008.13613.x | pages=925–938 | bibcode = 2008MNRAS.389..925T | arxiv = 0806.3263 | doi-access = free}}</ref> The secondary is itself a single-lined [[spectroscopic binary]] consisting of a {{solar mass|0.58|link=y}} companion and itself.<ref name = Tokovinin2008/> The system is located approximately 700 light years away.<ref name = GaiaDR3A>{{Cite DR3|3858258736489909632}}</ref><ref name = GaiaDR3B>{{Cite DR3|3858258736489910400}}</ref> The outer pair has a separation of 6.8" and both stars take roughly 23,000 years to orbit each other while the B subsystem takes 1,528 days to circle each other in a relatively [[orbital eccentricity|eccentric]] orbit.<ref name = Tokovinin2007>{{cite journal | last=Tokovinin | first=A. A. | last2=Gorynya | first2=N. A. | title=New spectroscopic components in multiple systems. V. | journal=Astronomy & Astrophysics | volume=465 | issue=1 | date = April 2007 | issn=0004-6361 | doi=10.1051/0004-6361:20066888 | s2cid = 34100030 | pages=257–261 | bibcode = 2007A&A...465..257T | doi-access = free}}</ref>

There are a few notable [[variable star]]s, including  [[25 Sextantis|25]], [[23 Sextantis]], and [[LHS 292]]. [[NGC 3115]], an edge-on [[lenticular galaxy]], is the only noteworthy [[deep-sky object]]. It also lies near the ecliptic, which causes the [[Moon]], and some of the planets to occasionally pass through it for brief periods of time.

The constellation is the location of the field studied by the [[Cosmic Evolution Survey|COSMOS project]], undertaken by the [[Hubble Space Telescope]].

==COSMOS project==
{{Gallery |align=center |title= |width=200 |height=200 |captionstyle=text-align:center;
|File:A gigantic cosmic bubble.tif|COSMOS-Gr30 is a particularly dense region in space that contains 10 individual galaxies<ref>{{cite web|title=A gigantic cosmic bubble|url=https://www.eso.org/public/images/potw1746a/|website=www.eso.org|access-date=13 November 2017}}</ref>
|File:Eso1524aArtist’s impression of CR7 the brightest galaxy in the early Universe.jpg|[[Cosmos Redshift 7]], brightest [[galaxy]] in the early [[universe]], is located in the constellation Sextans (artist concept)}}

[[Sextans B]] is a fairly bright [[dwarf irregular galaxy]] at magnitude 6.6, 4.3 million [[light-year]]s from [[Earth]]. It is part of the [[Local Group]] of galaxies.{{sfn|Levy|2005|p=178}}

[[CL J1001+0220]] is as of 2016 the most distant-known [[galaxy cluster]] at [[redshift]] z=2.506, 11.1 billion light-years from Earth.<ref name=AJ-828-1>{{cite journal |arxiv=1604.07404 |doi=10.3847/0004-637X/828/1/56 |title=Discovery of a galaxy cluster with a violently starbursting core at z=2.506 |journal=The Astrophysical Journal |volume=828 |number=1 |year=2016 |last1=Wang |first1=Tao |last2=Elbaz |first2=David |last3=Daddi |first3=Emanuele |last4=Finoguenov |first4=Alexis |last5=Liu |first5=Daizhong |last6=Schrieber |first6=Corenin |last7=Martin |first7=Sergio |last8=Strazzullo |first8=Veronica |last9=Valentino |first9=Francesco |last10=van Der Burg |first10=Remco |last11=Zanella |first11=Anita |last12=Cisela |first12=Laure |last13=Gobat |first13=Raphael |last14=Le Brun |first14=Amandine |last15=Pannella |first15=Maurilio |last16=Sargent |first16=Mark |last17=Shu |first17=Xinwen |last18=Tan |first18=Qinghua |last19=Cappelluti |first19=Nico | last20=Li |first20=Xanxia|page=56 |bibcode = 2016ApJ...828...56W |s2cid=8771287 |doi-access=free }}</ref>

In June 2015, astronomers reported evidence for [[Metallicity#Stars|population III stars]] in the [[Cosmos Redshift 7]] [[galaxy]] (at ''z'' = 6.60) found in Sextans. Such stars are likely to have existed in the very early [[universe]] (i.e., at high redshift), and may have started the production of [[chemical element]]s heavier than [[hydrogen]] that are needed for the later formation of [[planet]]s and [[life]] as we know it.<ref name="AJ-20150604">{{cite journal |last1=Sobral |first1=David |last2=Matthee |first2=Jorryt |last3=Darvish |first3=Behnam |last4=Schaerer |first4=Daniel |last5=Mobasher |first5=Bahram |last6=Röttgering |first6=Huub J. A. |last7=Santos |first7=Sérgio |last8=Hemmati |first8=Shoubaneh |title=Evidence For POPIII-Like Stellar Populations In The Most Luminous LYMAN-α Emitters At The Epoch Of Re-Ionisation: Spectroscopic Confirmation |date=4 June 2015 |journal=[[The Astrophysical Journal]] |doi=10.1088/0004-637x/808/2/139 |bibcode=2015ApJ...808..139S |volume=808 |issue=2 |pages=139|arxiv = 1504.01734 |s2cid=18471887 }}</ref><ref name="NYT-20150617">{{cite news |last=Overbye |first=Dennis |author-link=Dennis Overbye |title=Astronomers Report Finding Earliest Stars That Enriched Cosmos |url=https://www.nytimes.com/2015/06/18/science/space/astronomers-report-finding-earliest-stars-that-enriched-cosmos.html |date=17 June 2015 |work=[[New York Times]] |access-date=17 June 2015 }}</ref>
{{clear}}

==Depictions of the constellation==
{{Gallery |align=center |title= |width=200 |height=200 |captionstyle=text-align:center;
|File:SextansDoppelmayr.png|The constellation Sextans as depicted in [[Johann Gabriel Doppelmayr|Johann Doppelmayr]]'s Atlas Coelestis, c. 1730 (Plate 19, Southern Celestial Hemisphere).
|File:Sidney Hall - Urania's Mirror - Noctua, Corvus, Crater, Sextans Uraniæ, Hydra, Felis, Lupus, Centaurus, Antlia Pneumatica, Argo Navis, and Pyxis Nautica.jpg|Sextans and other constellations seen around [[Hydra (constellation)|Hydra]]. From ''[[Urania's Mirror]]'' (1825)
}}

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

==References==
{{Reflist}}
* {{cite web |ref={{sfnRef|IAU, ''The Constellations'', Sextans}} |title=Sextans |work=The Constellations |publisher=International Astronomical Union |url=https://www.iau.org/public/themes/constellations/#sex}}
* {{cite book |first = David H. |last = Levy |title = Deep Sky Objects |publisher = [[Prometheus Books]] |year = 2005 |isbn = 1-59102-361-0 |url-access = registration |url = https://archive.org/details/deepskyobjects00davi }}
* Ian Ridpath and Wil Tirion (2007). ''Stars and Planets Guide'', Collins, London. {{ISBN|978-0-00-725120-9}}. Princeton University Press, Princeton. {{ISBN|978-0-691-13556-4}}.

==Notes==
{{notelist}}

== External links ==
{{Commons}}
* [http://www.allthesky.com/constellations/sextans/ The Deep Photographic Guide to the Constellations: Sextans]
* [http://astrojan.nhely.hu/sextans.htm Clickable Sextans]
* [http://www.ianridpath.com/startales/sextans.html Star Tales – Sextans]

{{Stars of Sextans}}
{{Constellations}}
{{ConstellationsByHevelius}}
{{Portal bar|Astronomy|Stars|Outer space}}
{{Authority control}}
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{{DEFAULTSORT:Sextans}}
[[Category:Sextans| ]]
[[Category:Equatorial constellations]]
[[Category:Constellations listed by Johannes Hevelius]]