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Eta Aquarii (η Aqr, η Aquarii) is the Bayer designation for a star in the equatorial constellation of Aquarius. It is visible to the naked eye with an apparent visual magnitude of 4.04.〔 The distance to this star, as determined by parallax measurements, is about .〔 Eta Aquarii is near the radiant of a meteor shower named after it. Eta Aquarii has a stellar classification of B9IV-Vn,〔 which may indicate that it is beginning to evolve away from the main sequence into a subgiant as the supply of hydrogen at its core becomes exhausted. It is spinning rapidly with a high projected rotational velocity of 291 km/s.〔 This is causing an equatorial bulge, giving the star an oblate figure with a 24% larger radius at the equator than at the poles.〔 The Doppler effect from the rapid rotation is causing the absorption lines in the star's spectrum to blur, as indicated by the 'n' suffix in the star's classification. ==Etymology== This star sometimes called with the name Hydria, from the Greek word ‘υδρια (''hudria''), meaning "water jar".〔 (YILDIZ ADLARI SÖZLÜĞÜ - Mustafa Pultar (Hydria) )〕 Another name of this star is Deli, derived from Hebrew word דלי (''dali'') literally meaning "hard".〔 (YILDIZ ADLARI SÖZLÜĞÜ - Mustafa Pultar (Deli) )〕 This star, along with γ Aqr (Sadachbia), π Aqr (Seat) and ζ Aqr (Sadaltager / Achr al Achbiya), were al Aḣbiyah (الأخبية), the Tent.〔Davis Jr., G. A., ("The Pronunciations, Derivations, and Meanings of a Selected List of Star Names," )''Popular Astronomy'', Vol. LII, No. 3, Oct. 1944, p. 12.〕〔γ Aqr as Aoul al Achbiya or Prima Tabernaculorum (the first of luck of the homes or tents), π Aqr as Wasat al Achbiya or Media Tabernaculorum (the middle of luck of the homes or tents) and ζ Aqr as Achr al Achbiya or Postrema Tabernaculorum (the end of luck of the homes or tents). η Aqr should be designated as al Achbiya consistently, but it was not designated as the Arabian name except the name Hydria (Greek) or Deli (Hebrew)〕 In Chinese, (), meaning ''Tomb'', refers to an asterism consisting of η Aquarii, γ Aquarii, ζ Aquarii, π Aquarii.〔 ''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, η Aquarii itself is known as (, (英語:the Third Star of Tomb).)〔 (AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 16 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「Eta Aquarii」の詳細全文を読む スポンサード リンク
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