Achernar
 The position of Achernar (lower right). |
|
| Observation data Epoch J2000 Equinox J2000 |
|
|---|---|
| Constellation | Eridanus |
| Right ascension | 01h 37m 42.84548s |
| Declination | –57° 14′ 12.3101″ |
| Apparent magnitude (V) | 0.46(0.40 - 0.46) |
| Characteristics | |
| Spectral type | B6 Vep |
| U−B color index | −0.66 |
| B−V color index | −0.16 |
| Variable type | Be |
| Astrometry | |
| Radial velocity (Rv) | +16 km/s |
| Proper motion (μ) |
RA: 87.00 ± 0.58 mas/yr Dec.: −38.24 ± 0.50 mas/yr |
| Parallax (π) | 23.39 ± 0.57mas |
| Distance | 139 ± 3 ly (43 ± 1 pc) |
| Absolute magnitude (MV) | –1.46 |
| Details | |
| Mass | 6.7 M☉ |
| Radius | 7.3 × 11.4 R☉ |
| Luminosity | 3,150 L☉ |
| Surface gravity (log g) | 3.5 cgs |
| Temperature | ~15,000 K |
| Rotational velocity (v sin i) | 250 km/s |
| Age | 37.3 Myr |
| Other designations | |
| Database references | |
| SIMBAD | data |
Achernar /ˈeɪkərnɑːr/ is the name of the brightest component (by visual brightness) of the binary system designated Alpha Eridani (α Eridani, abbreviated Alpha Eri, α Eri), which is the brightest 'star' or point of light in, and lying at the southern tip of, the constellation of Eridanus, and the tenth-brightest in the night sky. The two components are designated Alpha Eridani A and Alpha Eridani B (known informally as Achernar B). As determined by the Hipparcos astrometry satellite, it is approximately 139 light-years (43 pc) from the Sun.
Of the ten apparent brightest stars in the night-time sky, Alpha Eridani is the hottest and bluest in color, due to Achernar being of spectral type B. Achernar has an unusually rapid rotational velocity, causing it to become oblate in shape. The secondary is smaller, of spectral type A, and orbits Achernar at a distance of roughly 12 astronomical units (AU).
α Eridani (Latinised to Alpha Eridani) is the system's Bayer designation. The designations of the two components - Alpha Eridani A and B - derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).
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