This autumn a bright star will begin to fade in a curious transformation that occurs every 27 years, and this time the help of citizens will be called upon.

Epsilon Aurigae is so bright it can be seen with the naked eye, even from urban areas. Since its discovery in 1821, it has remained somewhat of an enigma. Every 27 years it fades to half its brightness for several months before regaining normal brightness nearly two years later. Some astronomers think that it is an eclipsing binary but there are elements of the event that are not clearly understood.

Now astronomers have another chance to study the process again, for the star is expected to go through the puzzling transformation this autumn, and this time, observations by the public could help shed light on the stellar mystery. The National Science Foundation this week confirmed funding to support a project called Citizen Sky, which will recruit, train and coordinate public participation in studying epsilon Aurigae. Participants will even be shown how to present their findings in a professional way to publish in astronomy journals.

"This star is too bright to be observed with the vast majority of professional telescopes, so this is another area where public help is needed," says Arne Henden, director of the American Association of Variable Star Observers (AAVSO). The AAVSO has been training and coordinating amateur astronomers since 1911.

Citizen Sky is led by Robert Stencel, the William Herschel Womble Professor of Astronomy at Denver University, who studied Epsilon Aurigae's last event from 1982 to 1984. "This is truly an amazing star system," he says. "It contains both a supergiant star and a mysterious companion. If the supergiant was in our Solar System, its diameter would extend to Earth, engulfing us."

Epsilon Aurigae's companion only makes its presence known every 27 years but astronomers don't know what it is, they can only indirectly detect its presence. "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," adds Stencel. "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."

The Citizen Sky project will be much more than collecting data, giving participants real-world experience of original science research while contributing to the understanding of the Universe that we all live in. "Our goal is to introduce the public to authentic science and at the same time use this talent to help astronomers," says Hendon.

Citizen Sky was developed as part of the United States' International Year of Astronomy efforts.

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