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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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