Epoch J2000 Equinox J2000
|Right ascension||��20h 47m 40.55260s|
|Declination||−09° 29′ 44.7877″|
|Apparent magnitude (V)||3.77|
|Evolutionary stage||Main sequence|
|Spectral type||A1 V|
|U−B color index||+0.029|
|B−V color index||–0.001|
|Radial velocity (Rv)||−15.3±0.6 km/s|
|Proper motion (μ)|| RA: +33.98 mas/yr |
Dec.: -34.77 mas/yr
|Parallax (π)||15.70 ± 0.21 mas|
|Distance||208 ± 3 ly |
(63.7 ± 0.9 pc)
|Absolute magnitude (MV)||−0.46|
|Surface gravity (log g)||3.66±0.14 cgs|
|Metallicity [Fe/H]||−0.08±0.35 dex|
|Rotational velocity (v sin i)||118.0±5.9 km/s|
Epsilon Aquarii, Latinized from ε Aquarii, is a single star in the equatorial zodiac constellation of Aquarius, located near the western constellation border with Capricornus. It has the proper name Albali //, now formally recognized by the IAU. This is a white-hued star that is visible to the naked eye with an apparent visual magnitude of 3.77. Based upon parallax measurements taken during the Hipparcos mission, it is located at a distance of approximately 208 light-years (64 pc) from the Sun with an absolute magnitude of −0.46. The star is drifting closer with a radial velocity of −15 km/s.
This object is an A-type main-sequence star with a stellar classification of A1 V. It is an estimated 388 million years old with a high rate of spin, showing a projected rotational velocity of around 118 km/s. The elemental abundances in the stellar atmosphere are close to solar, with pronounced underabundances of aluminium and strontium. The star has three times the mass of the Sun and about 2.5 times the Sun's radius. It is radiating 138 times the luminosity of the Sun from its photosphere at an effective temperature of 9,622 K.
It bore the traditional name, Albali, from the Arabic البالع (albāli‘), meaning "the swallower". (See also Albulaan.) Along with Mu Aquarii (Albulaan) and Nu Aquarii (also Albulaan), they were al Bulaʽ (البلع), meaning "the Swallower". 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 Albali for this star on 12 September 2016, and it is now so included in the List of IAU-approved Star Names.
In the catalogue of stars in the Calendarium of Al Achsasi al Mouakket, it was designated Nir Saad Bula (نير سعد ألبلع nayyir sa'd al bulaʽ), which was translated into Latin as Lucida Fortunæ Dissipantis, meaning "the brightest of luck of the swallower".
In Chinese, 女宿 (Nǚ Sù), meaning Girl (asterism), refers to an asterism consisting of Epsilon Aquarii, Mu Aquarii, 4 Aquarii, 5 Aquarii and 3 Aquarii. Consequently, the Chinese name for Epsilon Aquarii itself is 女宿一 (Nǚ Sù yī, English: the First Star of Girl).
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