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 of a binary system. 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, this system is located at a distance of approximately 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 7.35AU.
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).
The system bears the traditional name of Achernar (sometimes spelled Achenar), derived from the Arabic آخر النهر , meaning "The End of the River". However, it seems that this name originally referred to Theta Eridani instead, which latterly was known by the similar traditional name Acamar, with the same etymology. The IAU Working Group on Star Names (WGSN) approved the name with the spelling Achernar for the component Alpha Eridani A on 30 June 2016 and it is now so included in the List of IAU-approved Star Names.
In Chinese caused by adaptation of the European Southern Hemisphere constellations into the Chinese system, 水委 (Shuǐ Wěi), meaning Crooked Running Water, refers to an asterism consisting of Achernar, ζ Phoenicis and η Phoenicis. Consequently, Achernar itself is known as 水委一 (Shuǐ Wěi yī, the First Star of Crooked Running Water).