 α Arietis shown in its constellation, Aries. |
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| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) |
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|---|---|
| Constellation | Aries |
| Right ascension | 02h 07m 10.4071s[1] |
| Declination | +23° 27′ 44.723″[1] |
| Apparent magnitude (V) | 1.98 to 2.04[2] |
| Characteristics | |
| Spectral type | K2IIICa-1[3] |
| U-B color index | +1.12[3] |
| B-V color index | +1.15[3] |
| V-R color index | 0.7[1] |
| R-I color index | +0.62[3] |
| Variable type | Suspected[2] |
| Astrometry | |
| Radial velocity (Rv) | −14.2 ± 0.9[1] km/s |
| Proper motion (μ) | RA: 190.73[1] mas/yr Dec.: −145.77[1] mas/yr |
| Parallax (π) | 49.48 ± 0.99[1] mas |
| Distance | 66 ± 1 ly (20.2 ± 0.4 pc) |
| Absolute magnitude (MV) | 0.48[note 1] |
| Details | |
| Mass | 2[4] M☉ |
| Radius | 15[4] R☉ |
| Luminosity (bolometric) | 90[4] L☉ |
| Temperature | 4,590[4] K |
| Rotational velocity (v sin i) | < 17[3] km/s |
| Other designations | |
| Database references | |
| SIMBAD | data |
Alpha Arietis (Alpha Ari / α Ari / α Arietis), which also has the traditional names Hamal and El Nath, is the brightest star in the constellation Aries.[3][4] Its Flamsteed designation is 13 Arietis, but this is very rarely used because it has a Bayer designation.
α Arietis has spectral type K2IIICa-1, which means that it is a K-type giant star, slightly cooler than the Sun and much larger. The Ca portion of the spectral type indicates that it shows calcium lines in its spectrum. It is estimated to be approximately twice as massive as the Sun and 15 times larger in diameter, and has around 90 times the Sun's bolometric luminosity.[4] The Hipparcos satellite indicates that α Arietis is about 66 light-years from Earth. Combined with its intrinsic brightness, this relatively small distance makes it shine at an apparent visual magnitude of about 2.00; it is the 47th brightest star in the night sky.[1] It has been reported to be slightly variable, by about 0.06 magnitude.[2]
Hamal's orientation with relation to the Earth's orbit around the Sun gives it a certain importance not apparent from its modest brightness. Between 2000 and 100 BCE, the apparent path of the Sun through the Earth's sky placed it in Aries at the vernal equinox, the point in time marking the start of spring.[5] This is why most astrology columns in modern newspapers begin with Aries.[6] While the vernal equinox has moved to Pisces since then due to precession of the equinoxes,[5] Hamal has remained in mind as a bright star near what was apparently an important place when people first studied the night sky.[4]
Etymology
The name Hamal (also written Hemal, Hamul, Ras Hammel) derives from the Arabic راس الحمل rās al-ħamal "head of the ram", in turn from the name for the constellation as a whole, Al Ħamal "the ram".[7]
The name El Nath comes from the Arabic النطح an-naţħ "the butting (horn)".[8]
Notes
- ^ From apparent magnitude and parallax.
References
- ^ a b c d e f g h i NAME HAMAL -- Variable Star, database entry, SIMBAD. Accessed on line December 16, 2008.
- ^ a b c NSV 725, database entry, New Catalogue of Suspected Variable Stars, the improved version, Sternberg Astronomical Institute, Moscow, Russia. Accessed on line December 16, 2008.
- ^ a b c d e f g HR 617, database entry, The Bright Star Catalogue, 5th Revised Ed. (Preliminary Version), D. Hoffleit and W. H. Warren, Jr., CDS ID V/50. Accessed on line December 16, 2008.
- ^ a b c d e f g Hamal, Stars, Jim Kaler. Accessed on line December 16, 2008.
- ^ a b pp. 151, 152, The Ever-changing Sky: A Guide to the Celestial Sphere, James B. Kaler, Cambridge, UK: Cambridge University Press, 2002, ISBN 0521499186.
- ^ p. 196, 365 Starry Nights: An Introduction to Astronomy for Every Night of the Year, Chet Raymo, New York: Simon and Schuster, 1982, ISBN 0671766066.
- ^ pp. 78, 80, Star-names and Their Meanings, Richard Hinckley Allen, New York: G. E. Stechert, 1899.
- ^ p. 80, Allen.
External links
- GJ 84.3, entry in the Gliese-Jahreiss catalogue (Preliminary Version of the Third Catalogue of Nearby Stars, W. Gliese and H. Jahreiss, 1991, CDS ID V/70A.)
- Hamal at Alycone Software's Star Data Pages.
- Image of Hamal from Aladin.
- The Constellations and Named Stars, Purple Hell.
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