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Epsilon Hydrae (ε Hya, ε Hydrae) is a Class G5, third-magnitude star system in the constellation Hydra. This stellar system is located about from Earth.〔 It is a multiple star system having at least four stellar components. The pair ε Hya AB form a binary star with an orbital period of 15 years and an angular separation of 0.2 arcseconds. Component ε Hya C is separated from the AB pair by 3 arcseconds. It is a spectroscopic binary system with a period of 9.9047 days〔 and an orbital eccentricity of 0.62,〔 while simultaneously orbiting ε Hya AB with a period of 870 years. The fourth component, ε Hya D, shares a common proper motion with the other components and thus is most likely a gravitationally-bound member of the system. It is separated from the AB pair by 19 arcseconds and has an estimated orbital period of around 10,000 years.〔 The primary, ε Hya A, is a giant star that is shining with 67 times the luminosity of the Sun. This energy is being radiated from the star's outer atmosphere at an effective temperature of 5,620 K,〔 giving it the yellow hue of a G-type star. It is rotating rapidly with a projected rotational velocity of 19 km s−1.〔 It has an X-ray luminosity of .〔 ==Name and etymology== This star, along with δ Hya (Lisan al Sudja), ζ Hya, η Hya, ρ Hya and σ Hya (Minhar al Shija), were Ulug Beg's Min al Azʽal, "Belonging to the Uninhabited Spot".〔 According to the catalogue of stars in the ''Technical Memorandum 33-507 - A Reduced Star Catalog Containing 537 Named Stars'', ''Min al Azʽal'' or Minazal were the title for five stars:δ Hya as ''Minazal I'', η Hya as ''Minazal II'', ε Hya as ''Minazal III'', ρ Hya as ''Minazal IV'' and ζ Hya as ''Minazal V'' (exclude σ Hya)〔 In Chinese, (), meaning ''Willow (asterism)'', refers to an asterism consisting of ε Hydrae, δ Hydra, σ Hydrae, η Hydrae, ρ Hydrae, ζ Hydrae, ω Hydrae and θ Hydrae〔 ''中國星座神話'', written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.〕 Consequently, ε Hydrae itself is known as (, (英語:the Fifth Star of Willow).)〔 (AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 28 日 )〕 In ancient Indian astronomy, the five-star cluster of Hydrae is collectively called Ashlesha (Ayilyam in southern India) Nakshatras The people of Groote Eylandt called Unwala, "The Crab", for the star cluster including this star, δ Hya (Lisan al Sudja), ζ Hya, η Hya, ρ Hya and σ Hya (Minhar al Shija).〔(''Encyclopaedia of the history of science, technology, and medicine in non-western cultures'' ), ed. Helaine Selin, Dordrecht, Kluwer Academic Publishers, 1997, p.105.〕 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「Epsilon Hydrae」の詳細全文を読む スポンサード リンク
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