Sadalsuud (Beta Aquarii)
Sadalsuud (Beta Aquarii) is a star in the constellation Aquarius, magnitude 2.9.
‘Luck of lucks’: the brightest star of Aquarius, a yellow supergiant astronomers use as a yardstick.
Sadalsuud means ‘luck of lucks’, from the Arabic sa‘d al-su‘ūd. In old Egyptian, Persian and Islamic lore the star was tied to the end of winter, when gentle, steady spring rains began — good fortune for anyone who farmed. Along the Euphrates its name was Kakkab Nammax: the Star of Mighty Destiny.
Behind the name is a yellow supergiant of spectral type G0 Ib, 48 times the Sun’s width and about 2,000 times as luminous, with a surface temperature close to the Sun’s. It is only about 56 million years old, but at five or six solar masses it has already used up its core hydrogen and is probably fusing helium into carbon. Too light to explode, it will most likely end as a heavy white dwarf, comparable to Sirius B.
Sadalsuud (Beta Aquarii) is 540 light-years away: the light we see from it set off around 1485, around the time Columbus crossed the Atlantic.
Did you know?
- A yardstick for starlight. Since 1943 Sadalsuud’s spectrum has been one of the fixed anchor points against which astronomers classify other stars. It is also a standard for measuring how fast stars move towards or away from us.
- Leaving the galactic plane. Sadalsuud, Sadalmelik and Eta Pegasi form a trio moving through space together, at right angles to the plane of the Milky Way.
- X-rays from a supergiant. NASA’s Chandra X-ray Observatory detected X-rays from Sadalsuud’s hot outer atmosphere — among the first ever caught from a yellow supergiant of its kind.
The brightest star of Aquarius, a pale yellow 3rd-magnitude supergiant. Sadalmelik, its near-twin in brightness and colour, lies about ten degrees to the north-east, and the globular cluster M 2 sits about five degrees due north.
When and where to see it
It is best placed in the evening sky around September, when it crosses the meridian at about 10 pm local time (around midnight in August). It can be seen from everywhere south of 84°N and never sets south of 84°S.
At its highest it stands 34° up from 50°N, 49° up from 35°N, 84° up from the equator, 61° up from 35°S.
Facts
- Type
- Star
- Constellation
- Aquarius
- Designations
- Beta Aquarii, β Aqr, 22 Aqr, HR 8232, HD 204867, HIP 106278
- Magnitude
- 2.9
- Position
- RA 21h 31.6m, Dec −5° 34′ (J2000)
- Spectral type
- G0Ib
- Colour
- yellow (B−V 0.82)
- Distance
- 540 light-years
- Discovered
- Known since antiquity
Open AstroPilot to see when Sadalsuud (Beta Aquarii) is highest tonight from your location, how easy it is with your telescope or binoculars, and an eyepiece view.