|
Eta Draconis (η Dra, η Draconis) is a star in the northern circumpolar constellation of Draco. Despite having an apparent visual magnitude of only +2.73,〔 it is the second brightest star in this generally faint constellation. Based upon parallax measurements collected during the Hipparcos mission, this star is located at a distance of about from Earth.〔 Eta Draconis is a large star with 2.55〔 times the mass of the Sun. The spectrum matches a stellar classification of G8 III,〔 with the luminosity class III indicating this is an evolved giant star that has exhausted the supply of hydrogen at its core. It reached this stage in only 550〔 million years because higher mass stars such as this consume the supply of hydrogen more rapidly than the Sun. The measured angular diameter of this star, after correction for limb darkening, is .〔 At the estimated distance of Eta Draconis,〔 this yields a physical size of about 11 times the radius of the Sun.〔 From its extended envelope, it is radiating around 60 times the luminosity of the Sun at an effective temperature of 5,055 K,〔 giving it the yellow glow of a G-type star.〔 A nearby stellar companion is located at an angular separation of 5.1 arcseconds from Eta Draconis. This is an 8.8 magnitude K-type main sequence star with a stellar classification of K2 V.〔 At the estimated distance of this star system, the two stars are separated by a physical distance of at least 140 AU and require at least a millennium to complete an orbit.〔 ==Name== η Draconis, together with ζ Dra (Al Dhibah), were Al Dhīʼbain, the Duo Lupi in Arabic, the Two Hyaenas or Wolves, lying in wait for the Camel's Foal, the little star Al Rubaʽ, protected by the Mother Camels.〔(Star Name - R.H Allen p. 202 )〕 In Chinese, (), meaning ''Left Wall of Purple Forbidden Enclosure'', refers to an asterism consisting of η Draconis, ι Draconis, θ Draconis, ζ Draconis, υ Draconis, 73 Draconis, γ Cephei 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, η Draconis itself is known as (, (英語:the Third Star of Left Wall of Purple Forbidden Enclosure).),〔 (AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 10 日 )〕 representing (), meaning ''The Second Premier''.〔 (English-Chinese Glossary of Chinese Star Regions, Asterisms and Star Name ), Hong Kong Space Museum. Accessed on line November 23, 2010.〕 Possibly, 少宰 (Shàozǎi) is westernized into Hea Tsae by R.H. Allen with meaning "the Lowest Steward" but it was for θ Dra〔(Star Name - R.H. Allen p. 210 )〕 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 Draconis」の詳細全文を読む スポンサード リンク
|