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Beta Draconis (β Draconis, β Dra) is the third brightest star in the northern circumpolar constellation of Draco. It has the traditional name Rastaban, which has also been used for Gamma Draconis.〔(Rastaban ), ''Stars'', Jim Kaler. Accessed on line September 17, 2008.〕〔pp. 207–208, (''Star-names and Their Meanings'' ), Richard Hinckley Allen, New York, London: G. E. Stechert, 1899.〕 With an apparent visual magnitude of 2.79,〔 it is bright enough to be easily seen with the naked eye. Based upon parallax measurements from the Hipparcos astrometry satellite,〔〔 it lies at a distance of about from Earth.〔 Compared to the Sun, this is an enormous star with six times the mass and roughly 40 times the radius. At this size, Beta Draconis is emitting about 950 times the luminosity of the Sun from its outer envelope at an effective temperature of 5,160 K,〔 giving it the yellow hue of a G-type star.〔 The spectrum matches a stellar classification of G2 Ib–IIa,〔 with the luminosity class notation Ib–IIa indicating it lies part way between the bright giant and supergiant stages of its stellar evolution. It is about 67 million years old.〔 This is a binary star system, with a binary star designation of ADS 10611, in which the supergiant is orbited by a dwarf companion once every four millennia or so.〔〔 ==Name== The traditional name, from the Arabic phrase ''ra's ath-thu'ban'' ("head of the serpent") is less commonly written Rastaben. It is also known as Asuia and Alwaid, the latter meaning "who is to be destroyed," though some trace it to Arabic ''al'awwad'' ("the lute player"). It is part of the asterism of the Mother Camels (Arabic ''al'awa'id''), along with γ Dra (Eltanin), μ Dra (Erakis) ν Dra (Kuma) and ξ Dra (Grumium), which was later known as the Quinque Dromedarii. In Chinese, (), meaning ''Celestial Flail'', refers to an asterism consisting of β Draconis, ξ Draconis, ν Draconis, γ Draconis and ι Herculis.〔 ''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, β Draconis itself is known as (, (英語:the Third Star of Celestial Flail).)〔〔 (香港太空館 - 研究資源 - 亮星中英對照表 ), Hong Kong Space Museum. Accessed on line November 23, 2010.〕〔(Alwaid ), ''Constellations of Words'', Anne Wright. Accessed on line September 17, 2008.〕 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「Beta Draconis」の詳細全文を読む スポンサード リンク
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