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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. ==Name and etymology== *The traditional name Polis is derived from a Coptic word meaning ''foal''. *In Chinese, (), 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 (, (英語:the Third Star of Dipper).)〔 (AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 11 日 )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Mu Sagittarii」の詳細全文を読む スポンサード リンク
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