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Gamma Cephei (γ Cep, γ Cephei), traditionally named Errai, Er Rai, and or Alrai, is a binary star system approximately 45 light-years away in the constellation of Cepheus. Gamma Cephei contains an apparent magnitude of 3.22. The visible part of the system is a stellar class K1III-IV orange subgiant star on its first ascent off the main sequence. It is about 6.6 billion years old (based on Fe/H metallicity).〔 Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified.〔 Gamma Cephei is the naked-eye star that will succeed Polaris as the Earth's northern pole star, due to the precession of the equinoxes. It will be closer to the northern celestial pole than Polaris around 3000 CE and will make its closest approach around 4000 CE. The "title" will pass to ι Cephei some time around 5200 CE. The star has a companion star with a mass approximately 0.409 times that of our Sun.〔 Gamma Cephei B is of stellar mass and is assumed to be of similar age to its primary. It is probably a red dwarf of class M4, 6.2 degrees of magnitude fainter than the K-type primary star.〔 ==Etymology== Gamma Cephei's traditional name derives from the Arabic الراعي ''ar-rā‘ī'', meaning "the shepherd". Confusingly, the star β Ophiuchi is sometimes also called Alrai, but it is more commonly known as ''Cebalrai'' or ''Kelb Alrai'', meaning "shepherd's dog". In Chinese, (), meaning ''Left Wall of Purple Forbidden Enclosure'', refers to an asterism consisting of γ Cephei, ι Draconis, θ Draconis, η Draconis, ζ Draconis, υ Draconis, 73 Draconis and 23 Cassiopeiae.〔 ''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, γ Cephei itself is known as (, (英語:the Seventh Star of Left Wall of Purple Forbidden Enclosure).),〔 (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.〕 representing (), meaning ''The Second Imperial Guard''〔 (English-Chinese Glossary of Chinese Star Regions, Asterisms and Star Name ), Hong Kong Space Museum. Accessed on line November 23, 2010.〕 or ''Minor Guard''〔(Richard Hinckley Allen: Star Names — Their Lore and Meaning: Cepheus )〕 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「Gamma Cephei」の詳細全文を読む スポンサード リンク
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