Sigma1 Ursae Majoris

Template:Other stars by Bayer designation Template:Starbox begin Template:Starbox image Template:Starbox observe Template:Starbox character Template:Starbox astrometry Template:Starbox detail Template:Starbox catalog Template:Starbox reference Template:Starbox end Sigma¹ Ursae Majoris (σ¹ UMa) is the Bayer designation for a solitary star in the northern circumpolar constellation of Ursa Major. With an apparent visual magnitude of 5.14 it is faintly visible to the naked eye on dark nights. Based upon an annual parallax shift of 6.26 mas, it is located roughly 520 light years from the Sun. At that distance, the visual magnitude of the star is diminished by an extinction factor of 0.06 due to interstellar dust.

This is an evolved K-type giant star with a stellar classification of K5 III. It is a suspected variable with an amplitude of 0.03 magnitude. The measured angular diameter of the star after correcting for limb darkening is Template:Val, which, at the estimated distance of this star, yields a physical size of about 46 times the radius of the Sun. The star is radiating around 560 times the solar luminosity from its outer atmosphere at an effective temperature of 3,940 K.

Naming

With π¹, π², σ², ρ, A and d, it composed the Arabic asterism Al Ṭhibā᾽, the Gazelle. According to the catalogue of stars in the Technical Memorandum 33-507 - A Reduced Star Catalog Containing 537 Named Stars, Al Ṭhibā were the title for seven stars : A as Althiba I, this star (π¹) as Althiba II, π² as Althiba III, ρ as Althiba IV, this star (σ¹) as Althiba V, σ² as Althiba VI, and d as Althiba VII.