Epsilon Aurigae 
Eclipses of the Sun and Moon are beautiful but fleeting -- they're over in a few hours. But astronomers have been watching an eclipse in another star system that's been underway for a year and a half -- and it still has a few weeks to go. That's because the eclipsing object is about three-quarters of a billion miles across.
The system is Epsilon Aurigae. It's about 2,000 light-years away, but it's so bright that it's visible to the unaided eye. Look for it high in the west this evening -- a modestly bright star to the lower left of bright yellow-orange Capella.
Epsilon fades every 27 years as a wide disk of dust passes in front of the star, blocking part of its light. During the last of these dimming acts, in the 1980s, astronomers thought they had the system figured out: It consisted of a central supergiant star, with two smaller stars concealed inside the disk.
But with the better technology available during the current eclipse, the model has changed. The star that we see is much less massive than anyone had thought. And the disk appears to conceal a single star that's even heavier than the other.
The disk may be debris from strong "winds" blown into space by both stars. The visible star appears to be nearing the end of its life, so it's blown much of its outer layers of gas into space. The concealed star may also be blowing thick winds into space -- helping create a long-lasting eclipse in this far-away system.
Script by Damond Benningfield, Copyright 2011