Almaaz or Epsilon Aurigae

Almaaz and Auriga

Right next to Capella in Auriga lies Almaaz (or Epsilon Aurigae).  Almaaz is a strange beastie.  It is an eclipsing binary.  Every 27 years the brightness of the binary drops by factor of two for nearly two years.   Its variability was discovered over 150 years ago but only recently has some consensus grown over the nature of the companion that blocks the light.

In 2009 observations with the Spitzer infrared telescope have found evidence that the primary is post-asymptotic giant star (like Mira but further along -- its pulsation period is about 66 days, much shorter than Mira) and that the secondary is a  B-star with a disk of material around it.   The system is actually in eclipse right now from 2009 to 2011.

The American Association of Variable Stars (AAVSO) have made it a special target during the current eclipse and you can check out a light curve up to today at this link.  Really Cool!