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| Gamma Aquilae | |
|---|---|
| Name | Gamma Aquilae |
| Other names | 30 Aquilae; Alshain |
| Constellation | Aquila |
| Epoch | J2000.0 |
| Ra | 19h 08m 20.6s |
| Dec | +10° 57′ 52″ |
| App mag v | 2.75 |
| Distance pc | 85 |
| Parallax mas | 11.82 |
| Spectral type | G8III |
| Mass | 3.5 |
| Radius | 40 |
| Luminosity | 553 |
| Temperature k | 4,550 |
| Gravity | 1.5 |
| Metallicity | −0.03 |
| Names | Alshain; 30 Aquilae; BD+10 4254; HD 178524; HIP 94141; HR 7254 |
Gamma Aquilae is a bright giant star in the northern constellation Aquila, commonly known by the traditional name Alshain. It is a naked-eye star used as a navigational reference in observational lists and appears in catalogs compiled by historical and modern institutions such as the Hipparcos mission and the Henry Draper Catalogue. With an apparent magnitude near 2.75 and a parallax measured by space astrometry, it is one of the more prominent evolved stars in the summer sky.
The Bayer designation uses a Greek-letter system developed by Johann Bayer for stars in constellations, assigning this object as Gamma within Aquila. The traditional name Alshain derives from Arabic sources and appears alongside other classical names preserved in compilations by Ptolemy and later catalogers. Modern catalog identifiers include numbers from the Henry Draper Catalogue, the Hipparcos Catalogue, the Bright Star Catalogue, and the Smithsonian Astrophysical Observatory Star Catalog. Professional datasets from missions such as Gaia and surveys like the Two Micron All Sky Survey also reference the star under unique survey identifiers.
Located in the celestial coordinates epoch J2000.0, the star lies near the celestial equator in Aquila just south of the Milky Way’s rich star fields referenced by observers including Galileo Galilei and later mapped by John Flamsteed. Its right ascension and declination place it within viewing season charts produced by observatories such as Royal Observatory Greenwich and the U.S. Naval Observatory. Alshain’s brightness makes it a useful landmark for amateur astronomers using charts by Sky & Telescope and guides from Royal Astronomical Society publications. Its position relative to neighboring stars such as Beta Aquilae and Altair helps in visual identification during summer and autumn nights in the Northern Hemisphere.
Gamma Aquilae is classified as a cool giant with photospheric parameters derived from spectroscopic surveys conducted by institutions like the European Southern Observatory and researchers at observatories including Kitt Peak National Observatory. Its effective temperature is around 4,550 K, yielding a yellow-orange hue noted in observational notes by observers such as William Herschel. Radius estimates, informed by interferometric measurements from facilities like the Palomar Observatory and the Very Large Telescope Interferometer, place it at roughly 40 times the Sun’s radius. Luminosity calculations using bolometric corrections and parallax from Hipparcos give a luminosity several hundred times solar. Surface gravity and metallicity values come from model atmosphere fits used in studies by teams at Harvard-Smithsonian Center for Astrophysics and similar institutions.
The spectral type G8III identifies the star as a G-type giant in the Morgan–Keenan system developed by William Wilson Morgan and Philip Keenan. Spectra recorded with instruments on telescopes operated by European Southern Observatory and the Palomar Observatory reveal absorption features typical of late-G giants, including prominent lines from neutral metals and molecular bands. Photometric monitoring by surveys such as the All Sky Automated Survey and targeted programs at McDonald Observatory indicate low-amplitude variability; it is sometimes cataloged as a suspected variable though not classified among definitive variable-star types like Cepheids or RR Lyrae in lists maintained by the International Astronomical Union.
As an evolved giant, the star has exhausted hydrogen in its core and expanded off the main sequence, following evolutionary paths modeled by codes used at Max Planck Institute for Astrophysics and the Geneva Observatory. Mass estimates in the literature, derived from isochrone fitting and asteroseismic analogues developed at Institut d’Astrophysique de Paris, suggest an initial mass of a few solar masses, consistent with a post-main-sequence age of several hundred million to about a billion years. Evolutionary status places it on the red-giant branch or possibly in a core-helium-burning phase, as indicated by comparisons with theoretical tracks by Eddington-era and modern stellar evolution groups.
High-resolution imaging and radial-velocity surveys carried out by teams at European Southern Observatory and the Keck Observatory find no confirmed close stellar companion; historical catalogs list it as a solitary bright giant in contrast to nearby multiple-star systems such as those in Vega or Altair. Wide-field catalogs like those produced by Hipparcos and Gaia identify distant optical neighbors but not a gravitationally bound multiple system. Searches for substellar companions through precision spectroscopy at facilities including Lick Observatory have not produced confirmed detections.
Alshain appears in star lore from Arabic astronomy preserved through translations associated with scholars like Al-Sufi and later in medieval European star atlases by Johannes Hevelius and Tycho Brahe. It features in navigation tables used by explorers from the age of sail such as those associated with James Cook and in modern star charts published by organizations like Royal Astronomical Society of Canada. The name and position of the star feature in cultural references compiled by historians at institutions like the Smithsonian Institution and in planetarium programming at venues such as the Hayden Planetarium. Category:Stars