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".[2] 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 09h 41m and 10h 51m, while the
declination coordinates are between +6.43° and −11.7°.[3] Since it is close to the ecliptic plane, the Moon and planets regularly cross the constellation, especially its northeastern corner.[citation needed]
John Flamsteed labeled 41 stars for the constellation.[4]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.[4] 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.[4] All together, there are 38 stars that are brighter than or equal to apparent magnitude 6.5.[a][6]
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.[10] The stars take 77.55 years to circle each other in an eccentric orbit[11] and the system is located 280±10 light-years away from the Solar System.[8] The separation of the stars is four-tenths of an
arcsecond,[11] making it difficult to observe without the use of a telescope with an aperture of 30 cm.
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.[16] The secondary is itself a single-lined
spectroscopic binary consisting of a 0.58
M☉ companion and itself.[16] The system is located approximately 700 light years away.[17][18] 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.[19]
In June 2015, astronomers reported evidence for
population III stars in the
Cosmos Redshift 7galaxy (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.[23][24]
Depictions of the constellation
The constellation Sextans as depicted in
Johann Doppelmayr's Atlas Coelestis, c. 1730 (Plate 19, Southern Celestial Hemisphere).
^
abcWagman, Morton (2003). Lost Stars: Lost, Missing and Troublesome Stars from the Catalogues of Johannes Bayer, Nicholas Louis de Lacaille, John Flamsteed, and Sundry Others. Blacksburg,
VA: The McDonald & Woodward Publishing Company. p. 290.
ISBN978-0-939923-78-6.
^
abHeintz, W. D. (March 1982), "Orbits of 16 visual binaries", Astronomy and Astrophysics Supplement Series, 47: 569–573,
Bibcode:
1982A&AS...47..569H.
^Crawford, D. L.; et al. (1971), "Four-color, H-beta, and UBV photometry for bright B-type stars in the northern hemisphere", The Astronomical Journal, 76: 1058,
Bibcode:
1971AJ.....76.1058C,
doi:
10.1086/111220.
^Mathys, G.; et al. (March 1986), "Photometric variability of some early-type stars", Astronomy and Astrophysics Supplement Series, 63 (3): 403–416,
Bibcode:
1986A&AS...63..403M.
^Kholopov, P. N.; et al. (April 1989), "The 69th Name-List of Variable Stars", Information Bulletin on Variable Stars, 3323 (3323): 1,
Bibcode:
1989IBVS.3323....1K.