Jupiter's Largest Moons Cast Rare Triple Shadow

Jupiter's three largest moons - lo, Europa and Callisto - cast a rare triple shadow Friday night on their giant host planet, a rare celestial event that won't occur again until 2032.

The triple-shadow transit was broadcast live on the website of the Griffith Observatory in California as well as posted to YouTube by astronomers.

It's not unusual for astronomers or even your avid backyard stargazers to see some of Jupiter's larger moons cast a shadow across the surface of the gas giant. However, even with over 60 confirmed moons, seeing more than one shadow at once is a rare and exciting sight. Triple-shadow transits only happen once or twice a decade on average, according to amateur astronomer Bob King, a writer for Sky and Telescope and community astronomer.

At least on the West Coast, Jupiter first rose in the night sky on Jan. 23 at 6:22 pm PST. The Observatory wrote that the first shadow to touch down was Callisto's - Jupiter's third largest moon - at 7:11 pm Friday night. It was soon followed by lo's at 8:35 pm, and then Europa's nearly two hours later at 10:27 pm.

All three shadows danced on Jupiter's face simultaneously for just 25 minutes, ending as the faster-traveling lo moved passed Jupiter.

A triple transit like this won't occur again until Dec. 30, 2032.

And if this remarkable spectacle wasn't enough, a second rare Jupiter shadow event also took place Friday when Io became eclipsed by slower-moving Callisto. Io's shadow on the planet merged with Callisto's for 19 minutes, showing as a single dark dot against the bright gaseous surface of Jupiter.

Galileo Galilei first discovered these massive moons back in 1610, sighting Io, Europa and Callisto, along with Ganymede, with his 30x magnification telescope.

And even though it is the smallest of this quartet, Europa has been of much interest to scientists as of late due to some Earth-like components. For instance, on recent study indicates that the moon's icy plate tectonics may be able to support life - an important consideration in the hunt for habitable worlds.

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