Epoch J2000 Equinox J2000
|Right ascension||22h 16m 50.03635s|
|Declination||–07° 46′ 59.8480″|
|Apparent magnitude (V)||4.175|
|Spectral type||G8 III–IV|
|U−B color index||+0.818|
|B−V color index||+0.983|
|Radial velocity (Rv)||–13.77 ± 0.17 km/s|
|Proper motion (μ)||RA: +118.80 mas/yr
Dec.: –22.18 mas/yr
|Parallax (π)||17.40 ± 0.23 mas|
|Distance||187 ± 2 ly
(57.5 ± 0.8 pc)
|Absolute magnitude (MV)||+0.23|
|Mass||2.39 to 2.78 M☉|
|Luminosity||72 to 83 L☉|
|Surface gravity (log g)||2.8 cgs|
|Metallicity [Fe/H]||+0.01 to +0.09 dex|
|Rotational velocity (v sin i)||1.6 km/s|
Theta Aquarii (θ Aqr, θ Aquarii) is the bayer designation for a star in the equatorial constellation of Aquarius. It has the traditional name Ancha; Medieval Latin for "the haunch". Visible to the naked eye at apparent magnitude 4.175, it is located at a distance of around 187 light-years (57 parsecs) from Earth. Since it is near the ecliptic it can be occulted by the Moon, or very rarely by planets.
In Chinese, 泣 (Qì), meaning Weeping, refers to an asterism consisting of θ Aquarii and ρ Aquarii. Consequently, θ Aquarii itself is known as 泣二 (Qì èr, English: the Second Star of Weeping.). Possibly, the name Lei meaning tears (weeping) in Chinese, was appear from the Chinese name for this star
Ancha belongs to the spectral class G8 with a luminosity class of III–IV suggesting that, at an age of 437 million years, this star is part way between the subgiant and giant stages of its evolution. Estimates of the star's mass range from 2.39 to 2.78 times the Sun's mass, with a radius of about 12 times that of the Sun. It is radiating from 72 to 83 times as much luminosity as the Sun from its enlarged outer envelope at an effective temperature of 4,864 K. At this heat, the star glows with the yellow hue of a G-type star.
- van Leeuwen, F. (November 2007), Validation of the new Hipparcos reduction, Astronomy and Astrophysics 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357.
- Gutierrez-Moreno, Adelina et al. (1966). "A System of photometric standards" 1. Publicaciones Universidad de Chile, Department de Astronomy. pp. 1–17. Bibcode:1966PDAUC...1....1G.
- Takeda, Yoichi et al. (August 2008), Stellar Parameters and Elemental Abundances of Late-G Giants, Publications of the Astronomical Society of Japan 60 (4): 781–802, arXiv:0805.2434, Bibcode:2008PASJ...60..781T, doi:10.1093/pasj/60.4.781.
- Massarotti, Alessandro et al. (January 2008), Rotational and Radial Velocities for a Sample of 761 HIPPARCOS Giants and the Role of Binarity, The Astronomical Journal 135 (1): 209–231, Bibcode:2008AJ....135..209M, doi:10.1088/0004-6256/135/1/209.
- Pizzolato, N.; Maggio, A.; Sciortino, S. (September 2000), Evolution of X-ray activity of 1-3 Msun late-type stars in early post-main-sequence phases, Astronomy and Astrophysics 361: 614–628, Bibcode:2000A&A...361..614P.
- tet Aqr -- Star, SIMBAD Astronomical Object Database (Centre de Données astronomiques de Strasbourg), retrieved 2012-06-30.
- (Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.
- (Chinese) 香港太空館 - 研究資源 - 亮星中英對照表, Hong Kong Space Museum. Accessed on line November 23, 2010.
- Richard Hinckley Allen: Star Names — Their Lore and Meaning: Aquarius
- The Colour of Stars, Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004, retrieved 2012-01-16.