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Zeta Sagittarii (Zeta Sgr, ζ Sagittarii, ζ Sgr) is the third brightest star system in the constellation Sagittarius, with an apparent visual magnitude of +2.59.〔 It has the traditional name Ascella. Based upon parallax measurements, the distance to Ascella is about .〔 Ascella is moving away from the Solar System with a radial velocity of 22 km s−1.〔 Some 1.0–1.4 million years ago, this system came within of the Sun.〔 This is a binary star system, with the two components orbiting each other over a period of 21 years at an eccentricity of 0.211. The combined mass of the system is 5.26 ± 0.37 times the mass of the Sun〔 and their blended stellar classification is A2.5 Va.〔 The system consists of a spectral class A2 giant with an apparent magnitude of +3.27, and an A4 subgiant with apparent magnitude of +3.48. The pair have a mean separation of 13.4 astronomical units (AU).〔 Ascella has a faint, 10th magnitude companion, separated from the primary by a distance of 75 arcseconds. ==Name and etymology== *The name Ascella from a Late Latin word meaning ''armpit''. *This star, together with : * *γ Sgr, δ Sgr, ε Sgr, λ Sgr, σ Sgr, τ Sgr and φ Sgr comprising the asterism ''Teapot''.〔 (【引用サイトリンク】 publisher = deepsky.astroinfo.org )〕〔(skywatchers )〕 * *φ Sgr, σ Sgr, χ Sgr and τ Sgr were ''Al Naʽām al Ṣādirah'' (النعم السادرة), the Returning Ostriches. * *σ Sgr and π Sgr may have been the Akkadian ''Gu-shi-rab‑ba'', the Yoke of the Sea.〔 * *τ Sgr, ν Sgr, ψ Sgr, ω Sgr and 60 Sgr were ''Al Udḥiyy'', the Ostrich's Nest.〔 *In the catalogue of stars in the ''Calendarium'' of Al Achsasi al Mouakket, this star was designated Thalath al Sadirah, which was translated into Latin as Tertia τού al Sadirah, meaning ''third returning ostrich''. *In Chinese, (), meaning ''Dipper'', refers to an asterism consisting of ζ Sagittarii, φ Sagittarii, λ Sagittarii, μ Sagittarii, σ Sagittarii and τ Sagittarii. Consequently, ζ Sagittarii itself is known as (, (英語:the First 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「Zeta Sagittarii」の詳細全文を読む スポンサード リンク
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