|
Gamma Ursae Majoris (Gamma UMa, γ Ursae Majoris, γ UMa) is a star in the constellation Ursa Major. It has the traditional name Phad, or Phecda. Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified.〔 Based upon parallax measurements with the Hipparcos astrometry satellite,〔〔 it is located at distance of around .〔 It is more familiar to most observers in the northern hemisphere as the lower-left star forming the bowl of the Big Dipper, together with Dubhe (upper-right), Merak (lower-right) and Megrez (upper-left). Along with four other stars in this well-known asterism, Phecda forms an actual loose, association of stars known as the Ursa Major moving group.〔 Like the other stars in the group, it is a main sequence star not unlike our Sun, although somewhat hotter, brighter and larger. Gamma Ursae Majoris is an Ae star, which is surrounded by an envelope of gas that is adding emission lines to the spectrum of the star;〔 hence the 'e' suffix in the stellar classification of A0 Ve.〔 It has 2.6〔 times the mass of the Sun, three times the Sun's radius,〔 and an effective temperature of 9,355 K in its outer atmosphere.〔 This star is rotating rapidly, with a projected rotational velocity of .〔 The estimated angular diameter of this star is about 0.92 mas.〔 It has an estimated age of 300 million years.〔 Phecda is located in relatively close physical proximity to the prominent Mizar-Alcor star system. The two are separated by an estimated distance of ; much closer than the two are from the Sun. The star Beta Ursae Majoris is separated from Gamma UMa by .〔 ==Name and etymology== *The traditional name ''Phad'', or ''Phecda'' comes from the Arabic phrase "fakhð ad-dubb" ("thigh of the bear").〔 *This star as ''Pulastya'', one of the Seven Rishis. *In Chinese, (), meaning ''Northern Dipper'', refers to an asterism consisting of γ Ursae Majoris, α Ursae Majoris, β Ursae Majoris, δ Ursae Majoris, ε Ursae Majoris, ζ Ursae Majoris and η Ursae Majoris. Consequently, γ Ursae Majoris itself is known as (, (英語:the Third Star of Northern Dipper)) and (, (英語:Star of Celestial Shining Pearl)).〔 (AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 15 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「Gamma Ursae Majoris」の詳細全文を読む スポンサード リンク
|