Eta Capricorni

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η Capricorni
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Capricornus
Right ascension 21h04m24.3s
Declination −19°51′18″
Apparent magnitude (V) +4.82
Distance 158 ± 11 ly
(48 ± 3 pc)
Spectral type A5V
Other designations
Arm, 22 Capricorni, HR 8060, HD 200499, Gl 816.2, BD−20°6115, HIP 104019, SAO 189986, GC 29419, CCDM J21044-1951

Eta Capricorni (η Cap, η Capricorni) is a binary star in the constellation Capricornus. It also has the traditional star name Arm. It is approximately 158 light years from Earth.

The primary component, η Capricorni A, is a white A-type main sequence dwarf with an apparent magnitude of +4.82. Its companion, η Capricorni B, has an apparent magnitude of +6.5 and is located 0.34 arcseconds from the primary.

Sometimes, this star is called by the name Armus.[1]

Chinese Name[edit]

In Chinese, 十二國 (Shíer Guó), meaning Twelve States, refers to an asterism which is represent twelve ancient states in the Spring and Autumn Period and the Warring States period, consisting of η Capricorni, φ Capricorni, ι Capricorni, 38 Capricorni, 35 Capricorni, 36 Capricorni, χ Capricorni, θ Capricorni, 30 Capricorni, 33 Capricorni, ζ Capricorni, 19 Capricorni, 26 Capricorni, 27 Capricorni, 20 Capricorni and 21 Capricorni.[2] Consequently, η Capricorni itself is known as 周一 (Zhou yī, English: the First Star of Zhou), meaning that this star (together with 21 Capricorni and β Serpentis in Right Wall of Heavenly Market Enclosure (asterism)[3][4]) represent Zhou () (possibly Chow, the dynasty in China).[5]