Achernar — Double Star in Eridanus

Achernar is the ninth brightest star in the sky at magnitude 0.46, a hot blue main-sequence star of spectral type B3Vpe in Eridanus. Located about 139 light-years from Earth, it has a luminosity of roughly 3,150 times solar. Achernar is the flattest star known — it spins so rapidly (at about 250 km/s) that its equatorial diameter is more than 50% larger than its polar diameter.

Achernar marks the southern end of the long, winding constellation Eridanus (the River). It is a brilliant blue-white star visible from latitudes south of about 33°N. From the southern hemisphere it is prominent in the evening sky during southern spring and summer. It lies roughly between the south celestial pole and Canopus. Best observed October through January.

The name Achernar comes from the Arabic 'akhir al-nahr,' meaning 'the end of the river,' referring to its position at the terminus of Eridanus. The ancient Greeks could see a different star at Eridanus's end — Theta Eridani (Acamar) — because precession has shifted the sky since their time, bringing Achernar higher for classical observers' latitudes.