Gamma Aquarii

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γ Aquarii is a bright star in the constellation Aquarius. It is also known by its common name of Sadachbia.

Naming and mythology

Like other bright stars in Aquarius, γ Aqr. caries in its name the Arabic for "lucky" (sa) which was associated with the stars of Aquarius because the sun passes them in its apparent path along the celestial sphere at a time when winter is coming to an end. The original Arabic name can be transliterated as Al Saʽd al Aḣbiyah and means "lucky star of hidden things".[1]

Observational attributes

Sadachbia shines with an apparent magnitude of +3.84 and can be found at celestial coordinates R.A. 22h 21m 39.4s and Dec. -1° 23ˈ 14ˈˈ. The star lies at a distance of some 70 light years as can be deduced from its parallax of 0.046ˈˈ[2]. This value for the distance may be too low and the true value could be closer to some 158 light years instead.[3]

Physical characteristics

The spectral class of Sadachbia is A0V and it has a surface temperature of some 9.500 Kelvin. Its mass is near 3 solar masses while the star's energy output equals some 62 solar luminosities.[3]

γ Aquarii is a spectroscopic binary star with a companion star of unknown properties an average of 0.40 astronomical units away. The orbital period is 58 days. In addition to this true companion star there is also a more distant star that is merely an optical companion and not physically related to the binary system.[4][3]

The star is also suspected to be variable, with a rather small amplitude of 0.05 magnitudes.[5]


  1. Star Names: Their Lore and Meaning, Richard H. Allen, Dover Publications 1963 (revised edition)
  2. Bright Star Catalog 5th revised edition, 1991
  3. 3.0 3.1 3.2 Jim Kaler's Stars, online at
  4. The Washington Visual Double Star Catalog, 1996
  5. Combined General Catalogue of Variable Stars, 1998