Epoch J2000.0 Equinox J2000.0 (ICRS)
|Right ascension||21h 05m 56.82783s|
|Declination||−17° 13′ 58.3021″|
|Apparent magnitude (V)||+4.07|
|Spectral type||A1 V|
|U−B color index||+0.01|
|B−V color index||−0.01|
|Proper motion (μ)||RA: +79.33 mas/yr
Dec.: −62.01 mas/yr
|Parallax (π)||20.11 ± 0.28 mas|
|Distance||162 ± 2 ly
(49.7 ± 0.7 pc)
|Surface gravity (log g)||±0.14 4.19cgs|
|Rotational velocity (v sin i)||104 km/s|
Theta Capricorni (θ Cap, θ Capricorni) is a white-hued star in the southern constellation of Capricornus, located about a half degree south of the ecliptic. Sometimes, this star is called by the name Dorsum, meaning the back (of the goat) in Latin. It can be seen with the naked eye, having an apparent visual magnitude of +4.07. Based upon an annual parallax shift of 20.11 mas as seen from the Earth, the star is located about 162 light years from the Sun.
This is an A-type main sequence star with a stellar classification of A1 V. It displays radial velocity variations that indicate it may be a binary star system. However, when the system was examined in the infrared, no companion was detected. Theta Capricorni has an estimated 2.24 times the mass of the Sun and around 2.7 times the Sun's radius. It is 152 million years old and is spinning fairly rapidly with a projected rotational velocity of 104 km/s. It is radiating 65 times the solar luminosity from its photosphere at an effective temperature of around 10,000 K.
In Chinese, 十二國 (Shíer Guó), meaning Twelve States, refers to an asterism which represents twelve ancient states in the Spring and Autumn period and the Warring States period, consisting of θ Capricorni, φ Capricorni, ι Capricorni, 38 Capricorni, 35 Capricorni, 36 Capricorni, χ Capricorni, 30 Capricorni, 33 Capricorni, ζ Capricorni, 19 Capricorni, 26 Capricorni, 27 Capricorni, 20 Capricorni, η Capricorni and 21 Capricorni. Consequently, θ Capricorni itself is known as 秦一 (Qin yī, English: the First Star of Qin), meaning that this star (together with 30 Capricorni and δ Serpentis in Right Wall of Heavenly Market Enclosure (asterism)) represents the state Qin (秦) (or Tsin)
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