Sextans

Sextans is a medium sized constellation bordering Leo to the north, touching on Hydra to the southwest, and Crater to the southeast. The recommended three-letter abbreviation for the constellation, as adopted by the International Astronomical Union in 1922, is "Sex".{{cite magazine | last=Russell | first=Henry Norris |author-link=Henry Norris Russell | title=The new international symbols for the constellations | magazine=Popular Astronomy | volume=30 | page=469 | bibcode=1922PA.....30..469R | date=1922 }} The official constellation boundaries, as set by Belgian astronomer 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°.{{cite web |title=International Astronomical Union {{!}} IAU |url=https://www.iau.org/public/themes/constellations/#sex |website=www.iau.org}} Since it is close to the ecliptic plane, the Moon and planets regularly cross the constellation, especially its northeastern corner.{{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}}

==Notable features==

{{See also|List of stars in Sextans}}

File:SextansCC.jpg

John Flamsteed labeled 41 stars for the constellation.{{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, VA | isbn = 978-0-939923-78-6 |pages=290}} Francis Baily intended to give Bayer designations to some of the stars but because none of them were above magnitude 4.5, he left them unlettered. Rather, it was Benjamin Apthorp Gould who lettered some of the stars. He labeled the five brightest stars using Greek letters Alpha (α) to Epsilon (ε) in his Uranometria Argentina. 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.{{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}}}}{{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 }}

• Alpha Sextantis is the brightest star in the constellation and the only star above the fifth magnitude with an apparent magnitude of 4.49. It is an ageing A-type star of spectral class A0 III{{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}} located 280{{±|20}} light-years away{{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=. }} from the Solar System. At the age of 385 million years,{{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 }} it is exhausting hydrogen at its core and leaving the main sequence.
• 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 stars with classes of A1 V and A4 V respectively.{{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 }} The stars take 77.55 years to circle each other in an eccentric orbit{{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=. }} and the system is located 280{{±|10}} light-years away from the Solar System. The separation of the stars is four-tenths of an arcsecond, making it difficult to observe without the use of a telescope with an aperture of 30 cm.
• β Sextantis is slightly fainter at magnitude 5.07;{{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=. }} it is said to be 364{{±|10}} light-years distant.{{Cite DR2|3782940437640705408}} 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.{{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=. }} It is suspected to be a Alpha² Canum Venaticorum variable with a period of 15.4 days.{{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=. }}

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

35 Sextantis is a triple star system consisting of two evolved K-type giants of equal mass, with both stars being twice as massive as the Sun.{{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}} The secondary is itself a single-lined spectroscopic binary consisting of a {{solar mass|0.58|link=y}} companion and itself. The system is located approximately 700 light years away.{{Cite DR3|3858258736489909632}}{{Cite DR3|3858258736489910400}} 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 eccentric orbit.{{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}}

There are a few notable variable stars, including 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 COSMOS project, undertaken by the Hubble Space Telescope.

{{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{{cite web|title=A gigantic cosmic bubble|url=https://www.eso.org/public/images/potw1746a/|website=www.eso.org|access-date=13 November 2017}}

|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-years 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.{{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 }}

In June 2015, astronomers reported evidence for 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 elements heavier than hydrogen that are needed for the later formation of planets and life as we know it.{{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 }}{{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 }}

{{clear}}

{{Gallery |align=center |title= |width=200 |height=200 |captionstyle=text-align:center;

|File:SextansDoppelmayr.png|The constellation Sextans as depicted in 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. From Urania's Mirror (1825)

}}

• Sextans (Chinese astronomy)

{{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}}.

{{notelist}}

{{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}}

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Category:Equatorial constellations

Category:Constellations listed by Johannes Hevelius