StarDate: February 6, 2009

You are missing some Flash content that should appear here! Perhaps your browser cannot display it, or maybe it did not initialize correctly.

audio/mpeg icon

A long, winding constellation twists its way to the west of bright Orion -- Eridanus, the river. Astronomers have been keeping a close eye on its brightest star, and recently found that there's more to it than meets the eye: the star is actually two stars.

Achernar marks the southern end of Eridanus. In fact, "Achernar" is an Arabic name that means "end of the river."

Even though it's 140 light-years away, Achernar shines brightly in Earth's night sky because it's hundreds of times brighter than the Sun. Unfortunately, though, it's so far south that few people in the United States can see it.

In 2006, astronomers using a large telescope in Chile discovered that Achernar has a companion star. The companion resembles Sirius, the brightest star in the night sky. Like Sirius, it's several times brighter than the Sun. But it's much fainter than Achernar's brighter star, so it's overpowered by the glare. That's why no one saw it until recently.

A few years before this discovery, astronomers studying Achernar had made another. They found that the star isn't round. Instead, it spins so fast that it's flattened itself out -- it's more than half again as wide through the equator as through the poles. That makes it the flattest star yet discovered.

Look for Eridanus to the right of Rigel, the bright blue star at the lower right corner of Orion. Eridanus streams to the south and west of Rigel, with Achernar out of view just below the horizon.

Script by Ken Croswell, Copyright 2008

For more skywatching tips, astronomy news, and much more, read StarDate magazine.

The one constant in the Universe: StarDate magazine


©2014 The University of Texas McDonald Observatory