Alpha Arietis
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| Observation data Epoch J2000 |
|
|---|---|
| Constellation | Aries |
| Right ascension | 02h 07m 10.4s |
| Declination | +23° 27′ 44″ |
| Apparent magnitude (V) | 2.2 |
| Spectral Characteristics | |
| Spectral type | K2 IIICa-1 |
| U-B color index | 1.12 |
| B-V color index | 1.15 |
| Variable type | Unknown |
| Astrometry | |
| Radial velocity (Rv) | -14 km/s |
| Proper motion (μ) | RA: 190.73 mas/yr Dec.: -145.77 mas/yr |
| Parallax (π) | 49.48 ± 0.99 mas |
| Distance | 66 ± 1 ly (20.2 ± 0.4 pc) |
| Absolute magnitude (MV) | 0.48 |
| Physical Characteristics | |
| Mass | 2 M☉ |
| Radius | 15 R☉ |
| Luminosity | 90 L☉ |
| Temperature | 4,590 K |
| Metallicity | ? |
| Rotation | <17 km/s. |
| Age | ? years |
| Other designations | |
Alpha Arietis (α Ari / α Arietis) is the brightest star in the constellation Aries. It also has the traditional names Hamal and El Nath. Its Flamsteed designation is 13 Arietis, but this is very rarely used because it is a bright star with a Bayer designation.
The name "Hamal" derives from the Arabic name for the constellation as a whole, Al Ħamal, "the sheep" or "the ram". Because of the confusion between star and constellation, the star is also (rarely) referred to as راس حمل rās al-ħamal, "head of the sheep/ram".
The star is a K2 IIICa giant star, which means it is an orangish, large star (some 55 times brighter, 18 times larger in diameter, and 4.5 times more massive than the sun), while the "Ca" notation indicates calcium lines in its spectrum. It is slightly variable, by about 0.05 magnitude.
The Hipparcos satellite indicates that Hamal is about 65.9 light-years from Earth. Combined with its intrinsic brightness, this relatively small distance makes the star shine at an apparent magnitude of 2.01, the 47th brightest star in the sky.
Hamal's orientation with relation to the Earth's orbit around the sun gives it a certain importance not apparent from its modest brightness. In antiquity, the apparent path of the sun through the Earth's sky places it in Aries at the start of spring (which is why most astrology columns in modern newspapers begin with Aries). While the equinox has moved to Pisces since then due to precession, Hamal has remained in mind as the brightest star at what was apparently an important place when people first studied the night sky.
