A super-bright star is gradually going dim, and scientists want YOU to help them find out why.

For nearly 200 years, astronomers have been wondering why the star epsilon Aurigae turns down its light once every 27 years. Based on careful observations of the star's periodic dimming, scientists believe that the supergiant star must have a mysterious companion that blocks its light periodically. But they still don't know what that companion is.

Epsilon Aurigae's next dip in brightness starts this fall, and telescope technology has come a long way since the star's last eclipse in 1982-84. This time, astronomers are also hoping they'll have the help of thousands of extra eyes: Starting today, a collaborative project called Citizen Sky is asking amateur astronomers to help solve the mystery of epsilon Aurigae.

"The star is too bright to be observed with the vast majority of professional telescopes," astronomer Arne Henden of the American Association of Variable Star Observers said in a press release, "so this is another area where public help is needed."

Because the star is so bright, even the most basic equipment — including the naked eye — can provide useful data. Normally the star can be seen from fall to spring in the Northern Hemisphere, even in urban areas with lots of light pollution. But beginning this fall, epsilon Aurigae is expected to gradually dim until it has lost half its light by early winter. The star will be dim during all of 2010 and then bounce back to its usual brightness by summer 2011.

Citizen Sky participants are being asked not just to collect data on the star's brightness, but also to join in on other aspects of the scientific process. A three-year grant from the National Science Foundation will provide funds to recruit and train a team of citizen scientists, who will be taught to analyze data, create and test their own hypotheses and even to write up their results.

Scientists are hoping observations of this year's eclipse will identify the star's curious companion, as as well resolve the mystery of a second perplexing object that appears to be headed for the star. "To make things even more fun, we also have some evidence of a substantial mass, perhaps a large planet, spiraling into the mysterious dark companion object," astronomer Robert Stencel of Denver University said in a press release. "Observations during the upcoming eclipse will be key to understanding this and predicting what will happen if the putative planet does eventually fall into the star."

To learn more, watch the video below (complete with Lite Brite illustrations!) or visit www.citizensky.org to find out how you can get involved.

Image: Artist's rendering of epsilon Aurigae by Brian Thieme/www.citizensky.org

Video: www.citizensky.org

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