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Beta Aquarii
Beta Aquarii (β Aqr, β Aquarii) is a double star in the constellation Aquarius. It has the traditional name Sadalsuud, from an Arabic expression سعد السعود ''sa‘d al-su‘ūd'', the "luck of lucks". Other spellings that are sometimes encountered are Sad es Saud, Sadalsund, and Saad el Sund.
In the catalogue of stars in the ''Calendarium of Al Achsasi Al Mouakket'', this star was designated Nir Saad al Saaoud, which was translated into Latin as Lucida Fortunæ Fortunarum (rather identic with R.H. Allen), meaning ''the brightest of luck of lucks''.〔
== Properties ==
Sadalsuud is the brightest star in Aquarius with an apparent magnitude of 2.87〔 and a stellar classification of G0 Ib.〔 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, it is located at a distance of about 540 light-years (160 parsecs) from the Earth.〔 The mass of this star is about 6.0 to 6.5 times the mass of the Sun, but it is emitting roughly 2,300 times the Sun's luminosity implying a radius that is 50 times that of the Sun.〔〔 It has an estimated age of 60 million years;〔 old enough for a star of this mass to evolve into a supergiant. The estimated effective temperature of the star's outer envelope is about 5,700 K,〔 giving it the characteristic yellow hue of G-type stars.〔
X-ray emissions from the corona of this star have been detected using the Chandra X-ray Observatory; among the first such detections of X-rays for a G-type supergiant. A secondary X-ray source discovered near Beta Aquarii probably has an extragalactic origin.〔 This star belongs to a group of three intermediate mass stars with a space velocity that is carrying them perpendicular to the plane of the galaxy. The other members of this grouping are Alpha Aquarii and Eta Pegasi.〔
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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