Alphard
 Alphard = α Hya (circled) in the constellation Hydra. |
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| Observation data Epoch J2000 Equinox J2000 |
|
|---|---|
| Constellation | Hydra |
| Right ascension | 09h 27m 35.2433s |
| Declination | −08° 39′ 30.969″ |
| Apparent magnitude (V) | +2.00 |
| Characteristics | |
| Spectral type | K3 II-III |
| U−B color index | +1.73 |
| B−V color index | +1.44 |
| Astrometry | |
| Radial velocity (Rv) | −4.3 km/s |
| Proper motion (μ) |
RA: −14.49 mas/yr Dec.: 33.25 mas/yr |
| Parallax (π) | 18.40 ± 0.78mas |
| Distance | 177 ± 8 ly (54 ± 2 pc) |
| Absolute magnitude (MV) | −1.69 ± 0.09 |
| Details | |
| Mass | 3.03 ± 0.36 M☉ |
| Radius | 50.5 ± 4.0 R☉ |
| Luminosity | 780 ± 78 L☉ |
| Surface gravity (log g) | 1.54 cgs |
| Temperature | 4,120 K |
| Metallicity [Fe/H] | −0.06 dex |
| Rotation | 2,991 days |
| Rotational velocity (v sin i) | 1.1 km/s |
| Age | (4.2 ± 1.6) × 108 years |
| Other designations | |
Alphard, also designated Alpha Hydrae (α Hydrae, abbreviated Alpha Hya, α Hya) is the brightest star in the constellation of Hydra.
α Hydrae (Latinised to Alpha Hydrae) is the star's Bayer designation.
The traditional name Alphard is from the Arabic الفرد (al-fard), "the solitary one", there being no other bright stars near it. It was also known as the "backbone of the Serpent" to the Arabs. In the catalogue of stars in the Calendarium of Al Achsasi Al Mouakket, it was designated Soheil al Fard, which was translated into Latin as Soheil Solitarius, meaning the bright solitary one. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016 included a table of the first two batches of names approved by the WGSN; which included Alphard for this star. It is now so entered in the IAU Catalog of Star Names.
The European astronomer Tycho Brahe dubbed it Cor Hydræ, Latin for 'the heart of Hydra'.
In Chinese, 星宿 (Xīng Xiù), meaning Star, refers to an asterism consisting of Alphard, τ1 Hydrae, τ2 Hydrae, ι Hydrae, 26 Hydrae, 27 Hydrae, HD 82477 and HD 82428. Consequently, Alphard itself is known as 星宿一 (Xīng Xiù yī), "the First Star of Star". In ancient China it formed part of an asterism called the "red bird".
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