Eta Capricorni

Eta Capricorni, Latinized from η Capricorni, is a binary star system in the southern constellation of Capricornus. It can be seen with the naked eye, having a combined apparent visual magnitude of +4.84. Based upon an annual parallax shift of 20.20 mas as seen from the Earth, the star is located about 161 light years from the Sun.

The pair orbit each other with a period of 27.85 years, a semimajor axis of 0.265 arc seconds, an eccentricity of 0.410. The primary member, component A, is a white-hued A-type main sequence star with an apparent magnitude of +5.02. Its companion, component B, has an apparent magnitude of +7.39.

Nomenclature
η Capricorni (Latinised to Eta Capricorni) is the system's Bayer designation. It also has the Flamsteed designation 22 Capricorni.

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. Consequently, the Chinese name for η Capricorni itself is 周一 (Zhou yī, the First Star of Zhou), meaning that this star (together with 21 Capricorni and β Serpentis in Right Wall of Heavenly Market Enclosure (asterism) ) represent Zhou (周) (possibly Chow, the dynasty in China).

Sometimes, this star is called by the name Armus in an astrological context.