Mu Sagittarii

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Mu Sagittarii
Diagram showing star positions and boundaries of the Sagittarius constellation and its surroundings
Cercle rouge 100%.svg

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
Polis, μ Sagittarii, μ Sgr, Mu Sgr, 13 Sagittarii, CCDM J18210-2950A, BD-21 4908, FK5 682, GC 24856, HD 166937, HIP 89341, HR 6812, IDS 18078-2105 A, PPM 268080, SAO 186497, WDS J18138-2104A.

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
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[edit]


External links[edit]