Alpha Aquarii
 Location of α Aquarii (circled) |
|
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) |
|
|---|---|
| Constellation | Aquarius |
| Right ascension | 22h 05m 47.03593s |
| Declination | −00° 19′ 11.4568″ |
| Apparent magnitude (V) | 2.942 |
| Characteristics | |
| Spectral type | G2 Ib |
| U−B color index | +0.699 |
| B−V color index | +0.971 |
| R−I color index | +0.49 |
| Astrometry | |
| Radial velocity (Rv) | 7.5 km/s |
| Proper motion (μ) |
RA: +18.25 mas/yr Dec.: −9.39 mas/yr |
| Parallax (π) | 6.23 ± 0.19mas |
| Distance | 520 ± 20 ly (161 ± 5 pc) |
| Absolute magnitude (MV) | –3.882 |
| Details | |
| Mass | 6.5 ± 0.3 M☉ |
| Radius | 77 ± 15 R☉ |
| Luminosity | 3,000 L☉ |
| Surface gravity (log g) | 1.76 ± 0.04 cgs |
| Temperature | 5,210 ± 100 K |
| Metallicity [Fe/H] | +0.17 dex |
| Rotational velocity (v sin i) | 6.7 ± 1.5 km/s |
| Age | 53 Myr |
| Other designations | |
| Database references | |
| SIMBAD | data |
Alpha Aquarii (α Aquarii, abbreviated Alpha Aqr, α Aqr), also named Sadalmelik, is a single star in the constellation of Aquarius. The apparent visual magnitude of 2.94 makes this the second-brightest star in Aquarius. Based upon parallax measurements made during the Hipparcos mission, this star is located at a distance of roughly 520 light-years (160 parsecs) from the Sun.
α Aquarii (Latinised to Alpha Aquarii) is the star's Bayer designation.
It bore the traditional name Sadalmelik, which derived from an Arabic expression سعد الملك sa‘d al-malik meaning "Luck of the king". The name Rucbah had also been applied to this star; though it shared that name with Delta Cassiopeiae. It is only one of two stars with ancient proper names to lie within a degree of the celestial equator. The origin of the Arabic name is lost to history. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalogue and standardize proper names for stars. The WGSN approved the name Sadalmelik for this star on 21 August 2016 and it is now so entered in the IAU Catalog of Star Names (Delta Cassiopeiae was given the name Ruchbah).
In Chinese, 危宿 (Wēi Xiù), meaning Rooftop (asterism), refers to an asterism consisting of Alpha Aquarii, Theta Pegasi and Epsilon Pegasi. Consequently, Alpha Aquarii itself is known as 危宿一 (Wēi Xiù yī, English: the First Star of Rooftop.)
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