We might be one step closer to answering some of the questions surrounding one of the strangest phenomena in the sky. Besides being home to Capella, the sixth-brightest star, the constellation Auriga harbors a real oddball known as Epsilon Aurigae. Every 27 years it undergoes a weird form of eclipse, causing it to lose half its brightness. Evidence suggests that an orbiting dark and disk-like body with a partly open center periodically moves across the face of the star.

A year ago, I wrote about the eclipse and its mysterious history. Scientists expected the eclipse to begin in late summer. Right on cue, changes started in August as the star's light began to diminish. Over the last few months, subsequent observations have confirmed Epsilon Aurigae is now at minimum brightness and will remain that way until sometime in March 2011.

The eclipsing disc and its partly open center are slightly tilted to our line of sight. We know this because at mid-eclipse, Epsilon Aurigae brightens up a little, but not enough to return to its normal magnitude. Then, the trailing half of the disk moves in and Epsilon Aurigae returns to minimum brightness for the final stage of eclipse.

An earlier hypothesis about nature of the disc suggested that it might be an infant solar system forming around an unseen central star. But that may not be the case, according to Donald Hoard of Caltech. He suggests that Epsilon Aurigae may actually be an aging star shedding some of its mass. The disk is created by material gravitationally captured by the companion star.

As assistant research scientist at the Spitzer Space Science Center, Hoard has worked with NASA's orbiting infrared Spitzer telescope to collect images of the enigmatic system. To avoid over-saturation of the telescope's sensor array and maintain sensitivity to the dark disk and dim companion star, the investigating team aimed Spitzer by placing Epsilon Aurigae off-center. Then they used the shortest exposure times possible. This strategy enabled them to confirm the existence of the disk.


Come join me this weekend for a look at Epsilon Aurigae and other celestial treats as New Mexico State Parks hosts two events as part of its award-winning Reach for the Stars program.

• At 7 p.m. Friday, I will be joined by members of the Capital City Astronomy Club on the terrace of the historic lodge at Hyde Memorial State Park. The evening will begin at with a green laser-guided tour of main stars and constellations followed by observing through telescopes. For more information and directions, call 983-7175.
• At 5 p.m. Saturday, I will be conducting a telescope workshop and star party at Cerrillos Hills State Park. Interested participants will be introduced to the basics of telescopes operation and how to use it under the night sky. The stargazing portion of the evening will begin at 7 p.m. For more information and directions, call 474-0196.
  

Local stargazer Peter Lipscomb operates Astronomy Adventures guided night sky tours and advocates for sensible and energy-efficient lighting practices through public outreach and education. Contact him at peter@astronomyadventures.com.