ARICNS data Constellation Boötes | Magnitude 4.05 Apparent magnitude (V) 4.05 | |
Similar Kappa Boötis, Iota Boötis, Mu Boötis, Gamma Cancri, 38 Boötis | ||
Theta Boötis (θ Boo, θ Boötis) is a star in the constellation Boötes. It has the traditional name Asellus Primus (Latin for "first donkey colt") and the Flamsteed designation 23 Boötis. This star, along with the other Aselli (ι Boo and κ Boo) and λ Boo, were Aulād al Dhiʼbah (أولاد الضّباع - aulād al dhiʼb), "the Whelps of the Hyenas".
In Chinese, 天枪 (Tiān Qiāng), meaning Celestial Spear, refers to an asterism consisting of θ Boötis, κ2 Boötis and ι Boötis. Consequently, θ Boötis itself is known as 天枪三 (Tiān Qiāng sān, English: the Third Star of Celestial Spear.)
Properties
Theta Boötis has apparent magnitude +4.05 and belongs to the spectral class F7V. It is approximately 47 light years from Earth. From about 4300 BC until 3942 BC, it was the closest star to the celestial north pole visible to the naked eye, although it was still too dim to be regarded as a pole star.
There is a nearby 11th magnitude optical companion star about 70 arcseconds away. This is a class M2.5 dwarf that is separated by a minimum of 1,000 AUs. It is uncertain whether they are gravitationally bound, but they do have a common motion through space and so the two stars probably share a common origin.