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Sigma Andromedae
Sigma Andromedae (σ And, σ Andromedae) is the Bayer designation for a star in the northern constellation of Andromeda. It has an apparent visual magnitude of +4.5,〔 which is bright enough to be seen with the naked eye from most locations. Parallax measurements made during the Hipparcos mission place it at a distance of about .〔 The magnitude of the star is diminished by 0.08 from extinction caused by intervening gas and dust.〔
This star has a stellar classification of A2 V,〔 which matches the spectrum of an A-type main sequence star. It is about 450 million years old〔 and is spinning rapidly with a projected rotational velocity of 123 km/s.〔 The interferometry-measured angular diameter of this star is 0.465 mas,〔 which, at its estimated distance, equates to a physical radius of about 2.1 times the radius of the Sun.〔 It is radiating 26〔 times the luminosity of the Sun from its outer atmosphere at a temperature of 8,929 K,〔 giving it the white-hued glow of an A-type star.〔
In the past, radial velocity variations have been reported, but this remains unconfirmed. The star does not show any significant photometric variations and is used as a ubvy standard star.〔 Sigma Andromedae is a candidate for membership in the stream of stars associated with the Ursa Major Moving Group. This is a set of stars that share a common motion through space, which suggests they originated together.〔
==Naming==
In Chinese, (), meaning ''Celestial Stable'', refers to an asterism consisting of σ Andromedae, θ Andromedae and ρ Andromedae. Consequently, σ Andromedae itself is known as (, (英語:the Third Star of Celestial Stable).)〔 (AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 18 日 )〕
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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