Theta Aurigae (θ Aur / θ Aurigae) is a binary star in the constellation Auriga. It is approximately 173 light-years from Earth. Rarely used proper names for this star include the Arabic name Maha-Sim or Mahasim, which is a variant of the Arabic name Al-Mi'sam meaning "wrist" that was used to describe both Eta Aurigae and Theta Aurigae
The primary, θ Aurigae A, is a white A-type main sequence dwarf with an apparent magnitude of +2.7. It's companion, θ Aurigae B, is a yellow G-type main sequence dwarf with an apparent magnitude of +7.2. The two stars are separated by 3.5 arcseconds. A third star, the 11th magnitude θ Aurigae C, is 49 arcseconds away, and is an optical companion.
The mean combined apparent magnitude of the system is +2.65 but the primary is an Alpha2 Canum Venaticorum type variable star so the system's brightness varies from magnitude +2.62 to +2.70 with a period of 1.37 days.
It is known as 五車四 (the Fourth Star of the Five Chariots) in Chinese.
|NAME||Right ascension||Declination||Apparent magnitude (V)||Spectral type||Database references|
|ADS 4566 B (BD+37 1380B)||05h 59m 42s||+37° 13' 00||14.4||G2V||Simbad|
|ADS 4566 C (BD+37 1380C)||05h 59m 39.4s||+37° 13' 11||10.7||Simbad|
|ADS 4566 D (BD+37 1379)||05h 59m 41.122s||+37° 14' 59.69''||12.1||Simbad|