Sigma2 Ursae Majoris

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Sigma2 Ursae Majoris
Ursa Major IAU.svg
Cercle rouge 100%.svg

Location of σ2 Ursae Majoris (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Ursa Major
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)
Spectral type F7IV-V+K2V
Other designations
σ2 Ursae Majoris, σ2 UMa, Sigma2 UMa, 13 Ursae Majoris, BD+67 577, GC 12619, HD 78154, HIP 45038, HR 3616, PPM 16933, SAO 14788, WDS J09104+6708AB .

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.).[1]


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