Edwin L. Aguirre Sky and Telescope
 The
Galileo spacecraft is making discoveries light-years away from
Jupiter. Courtesy NASA/JPL/Caltech.
Last June
the Galileo spacecraft orbiting Jupiter temporarily lost sight
of one of the reference stars it uses to maintain proper orientation.
Flight engineers suspected that the probe's star scanner had broken
down. "I spent about a week working on it," says Paul
Fieseler (Jet Propulsion Laboratory), "and concluded that
the star scanner wasn't broken, but perhaps the star was."
After a thorough check, Fieseler and his colleagues determined
that the star itself had briefly faded from view.
The star in
question is 2nd-magnitude Delta Velorum, part of the False Cross,
which consists of stars in Vela and Carina. Known to be a quadruple-star
system, it is one of 150 bright targets tracked by Galileo to
keep its low-gain antenna pointed at Earth. Follow-up observations
by amateur variable-star observer Sebastian Otero (Buenos Aires,
Argentina) and professional astronomer Christopher Lloyd (Rutherford
Appleton Laboratory) revealed that Delta Velorum is a hitherto
unknown eclipsing binary. Its brightest member is actually two
stars of similar brightness orbiting each other. Every 45 days
one mutually eclipses the other, causing Delta's total brightness
to dip from magnitude 1.96 to 2.3 for a few hours. Galileo apparently
lost track of the star during one of its periodic dimmings.
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