Eclipsing A Giant: rare triple-shadow of Jupiter's moons produces a double-eclipse

Monday, January 26, 2015, 9:19 AM - A pair of rare treats were in store for astronomers - backyard and professional - who aimed their telescope at the planet Jupiter this weekend.

As seen in the computer animation above, courtesy of the Griffith Observatory in Pasadena, Calif., three of Jupiter's largest moons - Io, Europa and Callisto - were in just the right positions in their orbits around the massive gas giant to cast their shadows onto the planet's cloud-tops at the same time. The first to cast its shadow was Callisto, the most distant of these moons, followed by the shadow of Io (fuzzy due to the plums of gas being erupted from the moon's surface), and then finally Europa's joined them to complete the triple-shadow.

Even more remarkable, though, is that Callisto actually eclipses Io during their transits. It's visible at 34 seconds into the animation, as Callisto briefly passes between Io and the Sun, and their shadows partially merge, forming a double-eclipse on Jupiter's face!

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While capturing just one of these shadowy transits is great, seeing three at the same time like this is fairly rare. Although it takes only days for these moons to make an orbit around Jupiter (the most distant of them, Callisto, only takes 16 days), meaning that they should come around onto the same side fairly often, according to the Griffith Observatory, this 'rare triple shadow' won't be visible again, at least from North America, for another 17 years!

Astronomer Will Gater was out with his telescope as the transit was happening, and captured some incredible views, even though the conditions in the atmosphere were only providing what he considered 'poor seeing'.

The above time-lapse was pieced together from the individual images Gator snapped during the transits. Check those out below (including a very cool little video showing not only the event, but also the ripples of distortion caused by the turbulent atmosphere above him):