Magnitude 4.8 | Constellation Ursa Major | |
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Sigma2 Ursae Majoris (Sigma2 UMa, σ2 Ursae Majoris, σ2 UMa) is a binary star approximately 66.7 light years from Earth. The primary component, is a yellow-white F-type subgiant with an apparent magnitude of +4.85. The companion is an orange K-type main sequence dwarf with an apparent magnitude of +8.16. The two stars have a semi-major axis on the sky of 6 arcseconds and have an orbital period of 1067 years. There is a third component, Sigma² Ursae Majoris C, 205 arcseconds from the primary which is thought to be a line-of-sight co-incidence.
Naming
In Chinese, 三師 (Sān Shī), meaning Three Top Instructors, refers to an asterism consisting of σ2 Ursae Majoris and ρ Ursae Majoris. Consequently, σ2 Ursae Majoris itself is known as 三師三 (Sān Shī sān, English: the Third Star of Three Top Instructors.).