Mu Sagittarii
 Location of μ Sagittarii (circled) |
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Sagittarius |
| Right ascension | 18h 13m 45.8s |
| Declination | −21° 03′ 32″ |
| Apparent magnitude (V) | +3.84 |
| Distance | > 3912 ly (> 920 pc) |
| Spectral type | B2III |
| Other designations | |
Mu Sagittarii (Mu Sgr, μ Sagittarii, μ Sgr) is a star system in the constellation Sagittarius. It also has the traditional name Polis.
The stars in the Polis system are designated Polis A through Polis E. Polis is more than 3000 light years from Earth.
The primary component in this system, Polis A, is a type B giant star with a total luminosity of 180,000 times that of the Sun and a radius of 115 times solar. Its mass is 23 times the solar mass while it has a surface temperature of 11,100 kelvins.
Polis A is an eclipsing binary, bringing the total of stars in the system to six. The primary component is a spectral type B8 supergiant and the companion is a type B2 giant. The orbital period of the binary is 180.55 days. Due to occultation of the primary by the companion, the apparent magnitude of Polis A varies between +3.84 and +3.96.
The remaining components are very weakly bound to the Polis system.
| Component | Apparent Magnitude |
Separation from Polis A |
Minimum distance from Polis A |
|---|---|---|---|
| Polis A | +3.84 | - | - |
| Polis B | +11.5 | 16.9 arcseconds | 42 200 AU or 0.67 ly |
| Polis C | +13.5 | 25.8 arcseconds | 64 500 AU or 1.02 ly |
| Polis D | +9.9 | 48.5 arcseconds | 121 200 AU or 1.92 ly |
| Polis E | +9.4 | 50.0 arcseconds | 125 000 AU or 1.98 ly |
Name and etymology
- The traditional name Polis is derived from a Coptic word meaning foal[citation needed].
- In Chinese, 斗 (Dǒu), meaning Dipper, refers to an asterism consisting of μ Sagittarii, φ Sagittarii, λ Sagittarii, σ Sagittarii, τ Sagittarii and ζ Sagittarii. Consequently, μ Sagittarii itself is known as 斗宿三 (Dǒu Sù sān, English: the Third Star of Dipper.)[1]
References
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