Achernar

Not to be confused with Achenar. For other uses, see Achernar (disambiguation).
Achernar
Location of Achernar (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Eridanus
Pronunciation /ˈeɪkərnɑːr/[1]
Right ascension 01h 37m 42.84548s[2]
Declination –57° 14′ 12.3101″[2]
Apparent magnitude (V) 0.40–0.46[3]
Characteristics
Spectral type B3 Vpe[4] + A1V-A3V[5]
U−B color index −0.66[6]
B−V color index −0.16[6]
Variable type Be[3]
Astrometry
Radial velocity (Rv)+16[7] km/s
Proper motion (μ) RA: 87.00±0.58[2] mas/yr
Dec.: −38.24±0.50[2] mas/yr
Parallax (π)23.39 ± 0.57 mas[2]
Distance139 ± 3 ly
(43 ± 1 pc)
Absolute magnitude (MV)−2.74±0.05[8]
Orbit[9]
Period (P)7.0389±0.0015 yr
Semi-major axis (a)0.17190±0.00025"
(7.35±0.18 AU)
Eccentricity (e)0.7258±0.0015
Inclination (i)30.32±0.35°
Longitude of the node (Ω)310.91±0.80°
Periastron epoch (T)2008.7582±0.0014
Argument of periastron (ω)
(secondary)		172.05±0.87°
Details
A
Mass6.0[9] M☉
Radius6.78 – 9.16[10] R☉
Luminosity3,493±429[9] L☉
Surface gravity (log g)2.772 – 3.561[10] cgs
Temperature12,673 – 17,124[10] K
Rotational velocity (v sin i)250[11] km/s
Age63[9] Myr
B
Mass2.0±0.1[9] M☉
Radius1.70±0.08[9] R☉
Luminosity17.5±5.1[9] L☉
Temperature9,064±624[9] K
Other designations
2 G. Eri, α Eri, 70 Eri, CD−57°334, FK5 54, HD 10144, HIP 7588, HR 472, SAO 232481,[12] 水委一[13]
Database references
SIMBADdata

Achernar is the brightest star in the constellation of Eridanus and the ninth-brightest in the night sky. It has the Bayer designation Alpha Eridani, which is Latinized from α Eridani and abbreviated Alpha Eri or α Eri. The name Achernar applies to the primary component[14] of a binary system.[5] The two components are designated Alpha Eridani A (the primary) and B (the secondary), with the latter known informally as Achernar B. As determined by the Hipparcos astrometry satellite,[15][16] this system is located at a distance of approximately 139 light-years (43 parsecs) from the Sun.[2]

Of the ten brightest stars in the night-time sky by apparent magnitude,[nb 1] Alpha Eridani is the hottest and bluest in color because it is spectral type B. Achernar has an unusually rapid rotational velocity, causing it to become oblate in shape. The secondary is smaller, is spectral type A, and orbits Achernar at a distance of 7.35 AU.

  1. ^ "Achernar". Merriam-Webster.com Dictionary. Merriam-Webster.
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