Beta Aquilae is a triple star system in the equatorial
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 ...
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 ...
that is Latinized from β Aquilae, and abbreviated Beta Aql or β Aql. This system is visible to the naked eye as a point-like source with an apparent visual magnitude of 3.87. Based on
parallax
Parallax is a displacement or difference in the apparent position of an object viewed along two different sightline, lines of sight and is measured by the angle or half-angle of inclination between those two lines. Due to perspective (graphica ...
measurements, it is located at a distance of 44.4 light-years. It is drifting closer to the Sun with a radial velocity of −40 km/s, and is predicted to approach to within in roughly 207,000 years.
Its two visible components are designated Beta Aquilae A and B. The former is formally named Alshain , the traditional name for the system.
Nomenclature
''β Aquilae'' (Latinised to ''Beta Aquilae'') is the system'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 ...
. The designations of the two components as ''Beta Aquilae A'' and ''B'' derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by 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 ...
(IAU).
The system bore the traditional name ''Alshain'' derived from the Perso-
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 ...
term الشاهين, ''aš-šāhīn'', meaning "the (peregrine) falcon", perhaps by
folk etymology
Folk etymology – also known as (generative) popular etymology, analogical reformation, (morphological) reanalysis and etymological reinterpretation – is a change in a word or phrase resulting from the replacement of an unfamiliar form by a mo ...
from the Persian ''šāhīn tarāzū'' (or possibly ''šāhīn tara zed''; see Gamma Aquilae), the Persian name for the asterismα, β and γ Aquilae. In 2016, the IAU organized a Working Group on Star Names (WGSN) to catalogue and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems. It approved the name ''Alshain'' for the component Beta Aquilae A on 21 August 2016 and it is now so included in the List of IAU-approved Star Names.
In the catalogue of stars in the ''Calendarium'' of Al Achsasi al Mouakket, this star was designated ''Unuk al Ghyrab'' (عنق ألغراب - ''únuq al-ghuraab''), which was translated into
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 ...
as ''Collum Corvi'', meaning ''the crow's neck''.
In Chinese, (), meaning '' River Drum'', refers to an asterism consisting of Beta Aquilae,
Altair
Altair is the brightest star in the constellation of Aquila (constellation), Aquila and the list of brightest stars, twelfth-brightest star in the night sky. It has the Bayer designation Alpha Aquilae, which is Latinisation of name ...
solar-like oscillations
Solar-like oscillations are oscillations in 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 ot ...
. Since 1943, the
spectrum
A spectrum (: spectra or spectrums) is a set of related ideas, objects, or properties whose features overlap such that they blend to form a continuum. The word ''spectrum'' was first used scientifically in optics to describe the rainbow of co ...
of this star has served as one of the stable anchor points by which other stars are classified.
This is an aging
subgiant
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 ...
star that has exhausted the supply of hydrogen at its core and is evolving into a
giant
In folklore, giants (from Ancient Greek: ''wiktionary:gigas, gigas'', cognate wiktionary:giga-, giga-) are beings of humanoid appearance, but are at times prodigious in size and strength or bear an otherwise notable appearance. The word ''gia ...
. Its
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 ...
has been precisely determined using
interferometry
Interferometry is a technique which uses the ''interference (wave propagation), interference'' of Superposition principle, superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important inves ...
at the
Very Large Telescope
The Very Large Telescope (VLT) is an astronomical facility operated since 1998 by the European Southern Observatory, located on Cerro Paranal in the Atacama Desert of northern Chile. It consists of four individual telescopes, each equipped with ...
and the CHARA array, the average of both measurements, combined with its estimated distance, result in a radius 3.096 times the radius of the Sun. It has a mass 24% greater than the Sun's, a luminosity 5.9 times that of the Sun, and an
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 ...
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 ...
s from the primary. It 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 ...
red dwarf
A red dwarf is the smallest kind of star on the main sequence. Red dwarfs are by far the most common type of fusing star in the Milky Way, at least in the neighborhood of the Sun. However, due to their low luminosity, individual red dwarfs are ...
Altair
Altair is the brightest star in the constellation of Aquila (constellation), Aquila and the list of brightest stars, twelfth-brightest star in the night sky. It has the Bayer designation Alpha Aquilae, which is Latinisation of name ...
) and Zhinü (織女, The Princess, Vega).
The Koori people of Victoria knew Beta and Gamma Aquilae as the
black swan
The black swan (''Cygnus atratus'') is a large Anatidae, waterbird, a species of swan which breeds mainly in the southeast and southwest regions of Australia. Within Australia, the black swan is nomadic, with erratic migration patterns dependent ...
wives of ''Bunjil'' (Altair), the
wedge-tailed eagle
The wedge-tailed eagle (''Aquila audax'') also known as the eaglehawk, is the largest bird of prey in the continent of Australia. It is also found in southern New Guinea to the north and is distributed as far south as the state of Tasmania. A ...