Sigma2 Ursae Majoris
Epoch J2000.0 Equinox J2000.0
|Right ascension||09h 10m 23.2s|
|Declination||+67° 08' 05"|
|Apparent magnitude (V)||4.85 + 8.16|
|Distance||66.7 ± 0.8 ly
(20.5 ± 0.3 pc)
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.
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.).
- Fuhrmann, Klaus (February 2008), "Nearby stars of the Galactic disc and halo - IV", Monthly Notices of the Royal Astronomical Society, 384 (1): 173–224, Bibcode:2008MNRAS.384..173F, doi:10.1111/j.1365-2966.2007.12671.x
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