AAVSO Alert Notice 398

Eclipse of epsilon Aurigae

July 10, 2009

The bright, long-period, eclipsing binary star epsilon Aurigae is
predicted to begin its next eclipse late July or early August of 2009.
The AAVSO is participating in a global campaign to record this eclipse
as part of the International Year of Astronomy 2009 celebrations,
organized by the Citizen Sky project (http://www.citizensky.org).

Epsilon Aurigae is now past solar conjunction and has reappeared as a
morning object. All observers -- both visual and instrumental -- are
encouraged to contribute observations of the eclipse during the next two
years, beginning immediately for morning observers. Observations are
urgently requested right now because it is less likely to be observed in
the morning, and the eclipse will begin within the next month.

Epsilon Aurigae is a bright (V ~ 3.0 out of eclipse), northern eclipsing
variable with a known period of 27.12 years. Eclipses have a duration
of several hundred days. It is not currently clear what the eclipsing
object is, although the leading theory is that it is a massive, opaque
dust disk surrounding either a single massive secondary star, or a pair
of stars in a tight orbit. Observations obtained during this eclipse
will help us to refine the properties of this enigmatic system.

Visual observers are particularly encouraged to observe epsilon Aurigae.
For experienced observers, please observe this star on a weekly basis,
using charts available via VSP from the AAVSO website. For novice
observers, we recommend participating in this observing program by
following the Citizen Sky 10-Star tutorial program, which provides a
simple training experience in variable star observing. The 10-star
tutorial is available at the following website:

http://www.citizensky.org/content/10-star-training

The rest of this notice and more information on epsilon Aurigae is here:

http://www.aavso.org/publications/alerts/alert398.shtml