Spinning star. Artwork of the star Achernar, which bulges because it spins very fast. All planets and stars bulge because of their spin, but Achernar is spinning so fast that its equatorial diameter is 1.6 times its polar diameter. Achernar is spinning at a speed of 225 kilometres a second. Achernar is the brightest star in the constellation Eridanus, and is also known as Alpha Eridani. It is 6 times as massive as the Sun, and is a hot blue star. The largest and smallest diameters, as measured from Earth, were 8.4 million and 5.4 million kilometres respectively (about 12 and 8 times the diameter of the Sun). This bulging was discovered in 2002, and is too extreme for standard stellar models.