Sextans is a faint, minor

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...

on the

celestial equator The celestial equator is the great circle of the imaginary celestial sphere on the same plane as the equator of Earth. By extension, it is also a plane of reference in the equatorial coordinate system. Due to Earth's axial tilt, the celestial ...

which was introduced in 1687 by Polish astronomer Johannes Hevelius. Its name is

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

for the astronomical sextant, an instrument that Hevelius made frequent use of in his observations.

Characteristics

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". The official constellation boundaries, as set by Belgian astronomer Eugène Delporte in 1930, are defined by a square. In the

equatorial coordinate system The equatorial coordinate system is a celestial coordinate system widely used to specify the positions of astronomical object, celestial objects. It may be implemented in spherical coordinate system, spherical or Cartesian coordinate system, rect ...

, the

right ascension Right ascension (abbreviated RA; symbol ) is the angular distance of a particular point measured eastward along the celestial equator from the Sun at the equinox (celestial coordinates), March equinox to the (hour circle of the) point in questio ...

coordinates of these borders lie between and , while the

declination In astronomy, declination (abbreviated dec; symbol ''δ'') is one of the two angles that locate a point on the celestial sphere in the equatorial coordinate system, the other being hour angle. The declination angle is measured north (positive) or ...

coordinates are between +6.43° and −11.7°. Since it is close to the ecliptic plane, the Moon and planets regularly cross the constellation, especially its northeastern corner.

Notable features

Stars

John Flamsteed labeled 41 stars for the constellation. Francis Baily intended to give

Bayer designation A Bayer designation is a stellar designation in which a specific star is identified by a Greek alphabet, Greek or Latin letter followed by the genitive case, genitive form of its parent constellation's Latin name. The original list of Bayer design ...

s 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 letter The Greek alphabet has been used to write the Greek language since the late 9th or early 8th century BC. It was derived from the earlier Phoenician alphabet, and is the earliest known alphabetic script to systematically write vowels as wel ...

s 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.

Bright stars

* 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 located 280

light-year A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by the International Astr ...

s away from the

Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Sola ...

. At the age of 385

million years Million years ago, abbreviated as Mya, Myr (megayear) or Ma (megaannum), is a unit of time equal to (i.e. years), or approximately 31.6 teraseconds. Usage Myr is in common use in fields such as Earth science and cosmology. Myr is also used ...

, it is exhausting

hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...

at its core and leaving the

main sequence In astronomy, the main sequence is a classification of stars which appear on plots of stellar color index, color versus absolute magnitude, brightness as a continuous and distinctive band. Stars on this band are known as main-sequence stars or d ...

. * γ Sextantis is the second brightest star in the constellation with an apparent magnitude of 5.05. It is a

binary star A binary star or binary star system is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved as separate stars us ...

consisting of two

A-type main-sequence star An A-type main-sequence star (A) or A dwarf star is a main-sequence (hydrogen burning) star of spectral type A and luminosity class (five). These stars have spectra defined by strong hydrogen Balmer absorption lines. They measure between 1 ...

s with classes of A1 V and A4 V respectively. The stars take 77.55 years to circle each other in an eccentric orbit and the system is located 280 light-years away from the Solar System. The separation of the stars is four-tenths of an

arcsecond A minute of arc, arcminute (abbreviated as arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of a degree. Since one degree is of a turn, or complete rotation, one arcminute is of a tu ...

, 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; it is said to be 364 light-years distant. 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. It is suspected to be a Alpha² Canum Venaticorum variable with a period of 15.4

days A day is the time period of a full rotation of the Earth with respect to the Sun. On average, this is 24 hours (86,400 seconds). As a day passes at a given location it experiences morning, afternoon, evening, and night. This daily cyc ...

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 giants of equal mass, with both stars being twice as massive as the Sun. The secondary is itself a single-lined spectroscopic binary consisting of a companion and itself. The system is located approximately 700 light years away. 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. There are a few notable

variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes systematically with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are ...

s, including 25, 23 Sextantis, and LHS 292. NGC 3115, an edge-on

lenticular galaxy A lenticular galaxy (denoted S0) is a Galaxy morphological classification, type of galaxy intermediate between an elliptical galaxy, elliptical (denoted E) and a spiral galaxy in galaxy morphological classification schemes. It contains a large-s ...

, is the only noteworthy deep-sky object. It also lies near the ecliptic, which causes the

Moon The Moon is Earth's only natural satellite. It Orbit of the Moon, orbits around Earth at Lunar distance, an average distance of (; about 30 times Earth diameter, Earth's diameter). The Moon rotation, rotates, with a rotation period (lunar ...

, 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 The Hubble Space Telescope (HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the Orbiting Solar Observatory, first space telescope, but it is one of the largest and most ...

COSMOS project

Sextans B is a fairly bright dwarf irregular galaxy at magnitude 6.6, 4.3 million

s from

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

. It is part of the Local Group of galaxies.

CL J1001+0220 CL or cl may refer to: Arts and entertainment * CL (rapper), (born Lee Chae-rin, 1991), singer and rapper, leader of the K-pop girl group 2NE1 * Creative Loafing, a newspaper publisher Brands and enterprises * Colgate-Palmolive's NYSE stoc ...

is as of 2016 the most distant-known galaxy cluster at

redshift In physics, a redshift is an increase in the wavelength, and corresponding decrease in the frequency and photon energy, of electromagnetic radiation (such as light). The opposite change, a decrease in wavelength and increase in frequency and e ...

z=2.506, 11.1 billion light-years from Earth. In June 2015, astronomers reported evidence for population III stars in the Cosmos Redshift 7

galaxy A galaxy is a Physical system, system of stars, stellar remnants, interstellar medium, interstellar gas, cosmic dust, dust, and dark matter bound together by gravity. The word is derived from the Ancient Greek, Greek ' (), literally 'milky', ...

(at ''z'' = 6.60) found in Sextans. Such stars are likely to have existed in the very early

universe The universe is all of space and time and their contents. It comprises all of existence, any fundamental interaction, physical process and physical constant, and therefore all forms of matter and energy, and the structures they form, from s ...

(i.e., at high redshift), and may have started the production of

chemical element A chemical element is a chemical substance whose atoms all have the same number of protons. The number of protons is called the atomic number of that element. For example, oxygen has an atomic number of 8: each oxygen atom has 8 protons in its ...

s heavier than

that are needed for the later formation of

planet A planet is a large, Hydrostatic equilibrium, rounded Astronomical object, astronomical body that is generally required to be in orbit around a star, stellar remnant, or brown dwarf, and is not one itself. The Solar System has eight planets b ...

s and

life Life, also known as biota, refers to matter that has biological processes, such as Cell signaling, signaling and self-sustaining processes. It is defined descriptively by the capacity for homeostasis, Structure#Biological, organisation, met ...

as we know it.

Depictions of the constellation

References

* * * Ian Ridpath and Wil Tirion (2007). ''Stars and Planets Guide'', Collins, London. . Princeton University Press, Princeton. .

Notes

External links

The Deep Photographic Guide to the Constellations: Sextans

{{DEFAULTSORT:Constellation, Sextans Equatorial constellations Constellations listed by Johannes Hevelius