Hellenica World


The Be star Achernar, flattened by extremely rapid rotation (*)


The position of Achernar.
Observation data
Epoch J2000
Right ascension 01h 37m 42.8s
Declination −57° 14' 12"
Apparent magnitude (V) 0.50
Spectral type B3 Vpe
U-B color index −0.66
B-V color index −0.20
Variable type Lambda Eridani
Radial velocity (Rv) 16 km/s
Proper motion (μ) RA: 88.02 mas/yr
Dec.: −40.08 mas/yr
Parallax (π) 022.68 ± 0.57 mas
Distance 144 ± 4 ly
(44 ± 1 pc)
Absolute magnitude (MV) −2.77
Mass 6–8 M
Radius ~10 R
Luminosity 3,311(bolometric) L
Temperature 14,510 K
Rotation 225–300 km/s
Age 1–5 × 108 years
Other designations
Alpha Eridani, α Eridani, HR 472, CD -57°334,

HD 10144, SAO 232481, FK5 54, HIP 7588.

Achernar (α Eri / α Eridani / Alpha Eridani), sometimes spelled Achenar, is the brightest star in the constellation Eridanus and the eighth-brightest star in the nighttime sky. It lies at the southern tip of the constellation.

Achernar is a bright, blue B-type star of six to eight solar masses lying approximately 144 light years away. Although classified as a main-sequence (dwarf) star, it is about 3,000 times more luminous than the Sun. Achernar is in the deep southern sky and never rises above 33°N. Achernar is best seen from the southern hemisphere in November; it is circumpolar below 33°S.

Until about March 2000, Achernar and Fomalhaut were the two first-magnitude stars furthest in angular distance from any other first-magnitude star in the celestial sphere. Antares, in the constellation of Scorpius, is now the most isolated first-magnitude star.

It is the least spherical star in the Milky Way studied to date. Achernar spins so rapidly that its equatorial diameter is more than 50% greater than its polar diameter.

The name comes from the Arabic آخر النهر ākhir an-nahr "river's end".

It is known as 水委一 (Shuǐwěiyī, the First Star of the Crooked Running Water) in Chinese.


* Achernar at solstation.com

* Achernar at absoluteastronomy.com

* Surface temperature and synthetic spectral energy distributions for rotationally deformed stars

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