Every six years, Earth spends a number of months passing through the orbital plane of Jupiter's moons. During the passage, amateur astronomers get to see a rare display of "mutual occultations." Jupiter's moons eclipse one another in plain view of backyard telescopes.

On May 25th, Mike Salway of Central Coast, Australia, watched Ganymede eclipse Io. Click to watch.

Images like these are unprecedented. Although Jupiter's moons put on the same kind of show in 2002-2003, no one recorded such clear pictures. "Imaging techniques and equipment have improved immensely over the past 6 years," notes Salway. "So this is the first year where amateurs are recording these events and producing detailed, high-resolution images of the phenomena."

If you missed the Ganymede-Io eclipse, don't worry. There are plenty more to come. Mutual occultations of Jupiter's moons will continue from now until nearly the end of the year. As part of the International Year of Astronomy, professional astronomers are organizing a worldwide observing campaign to record as many of these events as possible. Click here for details.