Beta Aquarii is a single[ yellow supergiant star in the constellation of Aquarius. It has the official name Sadalsuud ()][ It is drifting further away with a radial velocity of 6.5 km/s.][ The star serves as an IAU radial velocity standard.][
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Nomenclature
β Aquarii, Latinised to Beta Aquarii, is the star's Bayer designation.
It bore the traditional name Sadalsuud, from an Arabic expression سعد السعود ( sa‘d al-su‘ūd), the "luck of lucks". Other spellings that were sometimes encountered were 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.[ The International Astronomical Union Working Group on Star Names (WGSN)]
In Chinese, 虚宿 (Xū Xiù), meaning Emptiness (asterism), refers to an asterism consisting of Beta Aquarii and Alpha Equulei.[ Consequently, the Chinese name for Beta Aquarii itself is 虛宿一 (Xū Xiù Yī, ).][
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Sadalsuud is found in Hindu texts as Kalpeny and, in the context of the ancient Indian astronomy, Vedanga, is located in the 23rd Nakshatra Shravishthā, a lunar mansion which is ruled by Eight - the "deities of earthly abundance" . On the Euphrates, Sadalsuud was known as Kakkab Nammax, the Star of Mighty Destiny; that may have given origin to the title of the manzil, as well as to the Astrology' name for it — Fortuna Fortunarum.
Properties
β Aquarii is the brightest star in Aquarius with an apparent magnitude of 2.87[ and a stellar classification of G0 Ib.][ Since 1943, the stellar spectrum of this star has served as one of the stable anchor points by which other stars are classified.][ It has an estimated age of 56 million years;][ old enough for a star of this mass to evolve into a supergiant. The star has about five or six][ times the mass of the Sun, but it has expanded to 48 times the Sun's radius. It is most likely fusing helium into carbon in its core, and, with insufficient mass to explode as a supernova, will likely end up as a massive white dwarf comparable to Sirius B.][
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X-ray emissions from the stellar 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.][
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Optical companions
β Aquarii appears as a solitary star to the naked eye, but when viewed with a telescope is seen to have two faint optical companions. The first has an apparent magnitude of 11.0. In 1947, the position angle was observed at 321 degrees with a separation from Beta Aquarii of 35.4 arcseconds.[ and Gaia Data Release 2 shows the two companions to be around twice the distance of β Aquarii. All three stars have very different proper motions.][
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In mythology
In the context of older Mythology (i.e. Egyptian, Persian and Islamic mythology), Sadalsuud relates to the rising of the Sun when winter has passed (March) and the season of gentle, continuous rain has begun.
β and ξ Aquarii also constitute the Persian lunar mansion Bunda and the similar Copts mansion Upuineuti, the meaning of which is "the Foundation".
In Chinese mythology, β Aqr alone marks the xiu (Chinese lunar mansion) Heu, Hiu, or Hü, "the Void/Emptiness", anciently Ko, the central one of seven xiu which, taken together, were known as Heung Wu, the Black Tortoise, in the northern quarter of the sky.
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