Theta Boötis


Theta Boötis is a main sequence star in the constellation Boötes, about 47 light years away. It has the traditional name Asellus Primus and the Flamsteed designation 23 Boötis.

Nomenclature

θ Boötis, along with the other Aselli and λ Boo, were Aulād al Dhiʼbah', "the Whelps of the Hyenas".
In Chinese, 天枪, meaning Celestial Spear, refers to an asterism consisting of θ Boötis, κ2 Boötis and ι Boötis. Consequently, the Chinese name for θ Boötis itself is 天枪三

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.