Alpha Capricorni

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α¹ Cap and α² Cap by DSS2

Alpha Capricorni (α Capricorni, abbreviated Alpha Cap, α Cap) is an optical double star in the constellation of Capricornus. The two physically-unrelated components are designated α¹ Capricorni and α² Capricorni (also named Algedi[1]).

They are separated by 0.11° on the sky, and resolvable with the naked eye, similar to Mizar and Alcor. α¹ Capricorni is fainter (apparent magnitude 4.27) than α² Capricorni (apparent magnitude 3.58).


α Capricorni (Latinised to Alpha Capricorni) is the system's Bayer designation; α¹ and α² Capricorni, those of the two components.

Alpha Capricorni bore the traditional names Algedi, Algiedi, Al Giedi or Giedi, derived from the Arabic الجدي al-jady "the billy goat" or "kid". It also refers to the entire constellation of Capricornus. Giedi is sometimes also associated with Beta Capricorni. α¹ and α² Capricorni were also called Prima Giedi and Secunda Giedi, respectively. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[2] to catalogue and standardize proper names for stars. The WGSN approved the name Algedi for α² Capricorni on 21 August 2016 and it is now so entered in the IAU Catalog of Star Names.[1]

Alpha Capricorni is known as 牛宿二 (the Second Star of the Ox) in Chinese.


  1. ^ a b "IAU Catalog of Star Names". Retrieved 28 July 2016. 
  2. ^ IAU Working Group on Star Names (WGSN), International Astronomical Union, retrieved 22 May 2016. 

Kaler, Jim (2005). "Algedi". Retrieved July 27, 2005.

External links[edit]

Coordinates: Sky map 20h 18m 03.3s, −12° 32′ 41″