Sadalsuud

Beta Aquarii (β Aquarii, abbreviated Beta Aqr, β Aqr) is a star in the constellation of Aquarius. Based upon parallax measurements obtained during the Hipparcos mission, it is approximately 540 light-years (165 parsecs) from the Sun. The primary or 'A' component is officially named Sadalsuud /ˌsædəlˈsuːəd/, the traditional name for the system.

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 spectrum of this star has served as one of the stable anchor points by which other stars are classified. 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 48 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.