Alpha Gruis is the brightest

star A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...

in the southern

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 ...

of Grus. It is officially named Alnair; ''Alpha Gruis'' is the star's

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 ...

, which is Latinized from α Gruis and abbreviated α Gru. With an

magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...

of 1.74, it is one of the brightest stars in the sky and one of the fifty-eight stars selected for celestial navigation. Alpha Gruis is a single,

B-type main-sequence star A B-type main-sequence star (B V) is a main-sequence (hydrogen-burning) star of spectral type B and luminosity class V. These stars have from 2 to 16 times the mass of the Sun and surface temperatures between 10,000 and 30,000 K. B-type stars ...

located at a distance of .

Nomenclature

''α Gruis'' ( Latinised to ''Alpha Gruis'') is the star's

. (Its first depiction in a celestial atlas was in

Johann Bayer Johann Bayer (; 1572 – 7 March 1625) was a German lawyer and uranographer (celestial cartographer). He was born in Rain in 1572. In 1592, aged 20, he began his study of philosophy and law at the University of Ingolstadt, after which he ...

's ''

Uranometria is a star atlas produced by Johann Bayer. It was published in Augsburg in 1603 by Christoph Mang (''Christophorus Mangus'') under the full title (from Latin: ''Uranometria, containing charts of all the constellations, drawn by a new method an ...

'' of 1603.) It bore the traditional name ''Alnair'' or ''Al Nair'' (sometimes ''Al Na'ir'' in lists of stars used by navigators), from the

Arabic Arabic (, , or , ) is a Central Semitic languages, Central Semitic language of the Afroasiatic languages, Afroasiatic language family spoken primarily in the Arab world. The International Organization for Standardization (ISO) assigns lang ...

''al-nayyir'' "the bright one", itself derived from its Arabic name, ''al-nayyir min dhanab al-ḥūt (al-janūbiyy)'', "the bright one from the (southern) fish's tail" (see Aldhanab). Confusingly, ''Alnair'' was also given as the proper name for

Zeta Centauri Zeta Centauri, Latinisation of names, Latinized from ζ Centauri, also named Leepwal, is a binary star system in the southern constellation of Centaurus. With a combined apparent visual magnitude of +2.55, it is one of the List of stars ...

in an astronomical ephemerides in the middle of the 20th century. In 2016, the

International Astronomical Union The International Astronomical Union (IAU; , UAI) is an international non-governmental organization (INGO) with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreach, education, and developmen ...

organized a

Working Group on Star Names The International Astronomical Union (IAU) established a Working Group on Star Names (WGSN) in May 2016 to catalog and standardize proper names for stars for the international astronomical community. It operates under Division C – Education ...

(WGSN) to catalog and standardize proper names for stars. The WGSN approved the name ''Alnair'' for this star on 21 August 2016 and it is now so entered in the IAU Catalog of Star Names. Along with

Beta Gruis Beta Gruis (β Gruis, abbreviated Beta Gru, β Gru), formally named Tiaki , is the second brightest star in the southern constellation of Grus. It was once considered the rear star in the tail of the constellation of the (Southern) Fish ...

, Delta Gruis, Theta Gruis, Iota Gruis, and Lambda Gruis, Alpha Gruis belonged to

Piscis Austrinus Piscis Austrinus is a constellation in the southern celestial hemisphere. The name is Latin for "the southern fish", in contrast with the larger constellation Pisces, which represents a pair of fish. Before the 20th century, it was also known as ...

in traditional Arabic astronomy. In

Chinese Chinese may refer to: * Something related to China * Chinese people, people identified with China, through nationality, citizenship, and/or ethnicity **Han Chinese, East Asian ethnic group native to China. **'' Zhonghua minzu'', the supra-ethnic ...

, (), meaning '' Crane'', refers to an asterism consisting of Alpha Gruis,

, Delta² Gruis,

Epsilon Gruis ε Gruis, Latinised as Epsilon Gruis, is a blue-white hued star in the southern constellation of Grus. It is visible to the naked eye, having an apparent visual magnitude of 3.5. Based upon an annual parallax shift of 25.30 mas as ...

, Zeta Gruis, Eta Gruis, Iota Gruis, Theta Gruis, Mu¹ Gruis and Delta Tucanae. Consequently, Alpha Gruis itself is known as (, ). The Chinese name gave rise to another English name, ''Ke''.

Properties

Alpha Gruis has a

stellar classification In astronomy, stellar classification is the classification of stars based on their stellar spectrum, spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a Prism (optics), prism or diffraction gratin ...

of B6 V, although some sources give it a classification of B7 IV. The first classification indicates that this is a

B-type star In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...

on 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 ...

of stars that are generating energy through the

thermonuclear fusion Nuclear fusion is a reaction in which two or more atomic nuclei combine to form a larger nuclei, nuclei/neutron by-products. The difference in mass between the reactants and products is manifested as either the release or absorption of ener ...

of hydrogen at the core. However, a luminosity class of 'IV' would suggest that this is a

subgiant star A subgiant is a star that is brighter than a normal main-sequence star of the same spectral class, but not as bright as giant stars. The term subgiant is applied both to a particular spectral luminosity class and to a stage in the evolution of ...

; meaning the supply of hydrogen at its core is becoming exhausted and the star has started the process of

evolving Evolution is the change in the heritable characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, resulting in certai ...

away from the main sequence. It has no known companions. The measured

angular diameter The angular diameter, angular size, apparent diameter, or apparent size is an angular separation (in units of angle) describing how large a sphere or circle appears from a given point of view. In the vision sciences, it is called the ''visual an ...

of this star, after correcting for limb darkening, is . At the Alnair's distance from Earth of 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 ...

, this yields a physical size of times the

radius of the Sun Solar radius is a unit of distance used to express the size of objects in astronomy relative to the Sun. The solar radius is usually defined as the radius to the layer in the Sun's photosphere where the optical depth equals 2/3: 1\,R_ = 6.957\ti ...

. It is rotating rapidly, with a

projected rotational velocity Stellar rotation is the angular motion of a star about its axis. The rate of rotation can be measured from the spectrum of the star, or by timing the movements of active features on the surface. The rotation of a star produces an equatorial bu ...

of about 215 km/s providing a lower bound for the rate of

azimuth An azimuth (; from ) is the horizontal angle from a cardinal direction, most commonly north, in a local or observer-centric spherical coordinate system. Mathematically, the relative position vector from an observer ( origin) to a point ...

al rotation along the equator. This star has around four times the

Sun's mass The solar mass () is a frequently used unit of mass in astronomy, equal to approximately . It is approximately equal to the mass of the Sun. It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxies a ...

and is radiating roughly 520 times the

luminosity of the Sun The solar luminosity () is a unit of radiant flux ( power emitted in the form of photons) conventionally used by astronomers to measure the luminosity of stars, galaxies and other celestial objects in terms of the output of the Sun. One nominal s ...

. The

effective temperature The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation. Effective temperature is often used as an estimate of a body's surface temperature ...

of Alnair's outer envelope is 14,245 K, giving it the blue-white hue characteristic of B-type stars. The abundance of elements other than

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 ...

and

helium Helium (from ) is a chemical element; it has chemical symbol, symbol He and atomic number 2. It is a colorless, odorless, non-toxic, inert gas, inert, monatomic gas and the first in the noble gas group in the periodic table. Its boiling point is ...

, what astronomers term the

metallicity In astronomy, metallicity is the Abundance of the chemical elements, abundance of Chemical element, elements present in an object that are heavier than hydrogen and helium. Most of the normal currently detectable (i.e. non-Dark matter, dark) matt ...

, is about 74% of the abundance in the

Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

. Based on the estimated age and motion, it is a member of the

AB Doradus moving group AB Doradus Moving Group is a group of about 30 associated stars that are moving through space together with the star AB Doradus. A moving group is distinguished by its members having about the same age, composition (or metallicity) and motion throug ...

that share a common motion through space. This group has an age of about 70 million years, which is consistent with α Gruis's 100-million-year estimated age (allowing for a margin of error). The space velocity components of this star in the

Galactic coordinate system The galactic coordinate system is a celestial coordinate system in spherical coordinates, with the Sun as its center, the primary direction aligned with the approximate center of the Milky Way Galaxy, and the fundamental plane (spherical coordin ...

are 'U'', ''V'', ''W''= , , .

Notes

References

External links

* {{DEFAULTSORT:Alpha Gruis B-type main-sequence stars Grus (constellation) Gruis, Alpha 8425 CD-47 14063 0848.2 209952 109268 Alnair Gruis, 028