Alpha Capricorni (α Capricorni, abbreviated Alpha Cap, α Cap) is an

optical double In observational astronomy, a double star or visual double is a pair of stars that appear close to each other as viewed from Earth, especially with the aid of optical telescopes. This occurs because the pair either forms a binary star (i.e. a ...

star in the

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 ...

Capricornus Capricornus is one of the constellations of the zodiac. Its name is Latin for "horned goat" or "goat Horn (anatomy), horn" or "having horns like a goat's", and it is commonly represented in the form of a sea goat: a mythical creature that is hal ...

. The two physically unrelated components are designated: * α¹ Capricorni * α² Capricorni (also named Algedi). They are separated by 0.11° on the sky, and resolvable with the naked eye, The separation is , or 0.105°. similar to

Mizar and Alcor Mizar and Alcor are two stars forming a naked eye double in the handle of the Big Dipper (or Plough) asterism in the constellation of Ursa Major. Their magnitudes are 2.2 and 3.9, and the pair can easily be seen without the aid of a telescope. M ...

. α¹ Capricorni is fainter (apparent magnitude 4.27) than α² Capricorni (apparent magnitude 3.58).

Nomenclature

''α Capricorni'' ( Latinised to ''Alpha Capricorni'') 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 ...

; ''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 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 ...

''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 Beta Capricorni (β Capricorni, abbreviated Beta Cap, β Cap) is a multiple star system in the constellation of Capricornus and located 328 light-years from the Sun. Because it is near the ecliptic, Beta Capricorni can be occulted by the Mo ...

. ''α¹'' and ''α² Capricorni'' were also called ''Prima Giedi'' and ''Secunda Giedi'', respectively. In 2016, 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 ...

organized a

Working Group on Star Names The International Astronomical Union (IAU) established a Working Group on Star Names (WGSN) in May 2016 to catalog and standardize proper names for stars for the international astronomical community. It operates under Division C – Education ...

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

Chinese astronomy Astronomy in China has a long history stretching from the Shang dynasty, being refined over a period of more than 3,000 years. The Ancient China, ancient Chinese people have identified stars from 1300 BCE, as Chinese star names later categori ...

References

External links

* * Kaler, Jim
"Algedi"
Retrieved December 5, 2016. {{SIA , astronomical objects Capricorni, Alpha Capricornus Double stars