Alpha Aquarii

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α Aquarii, also known as Sadalmelik, is the second brightest star in the constellation Aquarius.

Naming and mythology

Sadalmelik is derived from the Arabic Al Saʽd al Malik which translates as lucky star of the king(dom). The origin of this name has been lost over time but it is in line with some other stars in the same constellation whose names contain the Arabic for lucky, Sa.[1]

Observational attributes

α Aquarii lies just south of the celestial equator at coordinates R.A. 22h 5m 47.0s and Dec. -00° 19ˈ 11ˈˈ. [2]Its parallax of 0.012ˈˈ indicate a distance from Earth of no more than 270 light years but the true value appears to be closer to 750 light years instead.[3] The star shines with an apparent magnitude of +2.96[2]

Physical characteristics

The spectral class of this unusual star is G2Ib while the distance and apparent magnitude indicate it has a total luminosity some 3.000 that of the sun and a surface temperature, as the spectral type would indicate, that is similar to the sun's. Sadalmelik is therefore considered to be a yellow supergiant star whose diameter may be 60 times the solar diameter.[3] Unlike many similar stars, α Aqr. is not classed a Cepheid variable although its true variable nature has yet to be determined.

Sadalmelik has a distant companion star of magnitude +12, located some 113ˈˈ away.[4]


  1. Star Names: Their Lore and Meaning, Richard H. Allen, Dover Publications 1963 (revised edition)
  2. 2.0 2.1 Bright Star Catalog 5th revised edition, 1991
  3. 3.0 3.1 Jim Kaler's Stars, online at
  4. The Washington Visual Double Star Catalog, 1996