Achernar

Achernar is the brightest star in the constellation Eridanus and the ninth brightest in the night sky at magnitude 0.46. It is a blue main-sequence star of spectral type B6V, located about 139 light-years from Earth. Achernar is roughly 6-7 times the mass of the Sun and about 3,000 times more luminous. It is one of the flattest stars known, spinning so rapidly (at about 250 km/s at its equator) that its equatorial diameter is about 56% larger than its polar diameter.

Achernar marks the southern end of the long, winding constellation Eridanus (the River). It is visible only from latitudes south of about 33°N. Its brilliant blue-white color and isolated position make it easy to identify from the Southern Hemisphere. There are few other bright stars in its immediate vicinity, which makes it stand out dramatically. Best observed from October through January from southern latitudes.

The name Achernar derives from the Arabic 'Akhir an-Nahr' meaning 'the end of the river,' referring to its position at the southern terminus of Eridanus. Because of its far southern declination (-57°), it was unknown to ancient Greek and Roman astronomers, who instead placed the end of their river constellation at the star Acamar (Theta Eridani). Achernar was added to European star catalogs after the great southern voyages of exploration.