Images: Galileo Project, Voyager Project

These are Jupiter's four large Galilean moons. Starting from left to right the moons are Io, Europa, Ganymede, and Callisto. This order is also the order of increasing distance from Jupiter. These are big moons indeed which attend the largest planet. The smallest of the lot, Europa, is the size of Earth's moon while Ganymede is the largest moon in the Solar System. In fact, Ganymede with a diameter of 3,100 miles, is larger than the planets Mercury and Pluto. Battered Callisto's image was recorded during the 1979 flyby of Voyager. The other portraits were taken by the Galileo spacecraft which began exploring the Jovian system in 1995.

Every six years the Earth lies in the orbital plane of Jupiter's moons. In 2003 our line of sight was in the same plane as the orbits of Jupiter's bright moons. The orbital shifting of these moons grabbed the attention of those with telescopes during this close approach of Jupiter.

Whenever you think of Jupiter, think "I eat green caterpillars." Why?

Well, with a cheap telescope or even a pair of binoculars you can watch the four largest of Jupiter's 40 moons [63 moons update] as they change position from night to night. They'll look like tiny pinpoints of light although three of them are actually larger than our Moon. Their names are Io, Europa, Ganymede and Callisto and when they're all lined up together on one side of Jupiter the phrase 'I Eat Green Caterpillars' will help you remember their order out from Jupiter. I for Io, E for Europa, G for Ganymede and C for Callisto. It's fun to watch them change position … from night to night. Happy green caterpillaring and Keep Looking Up! Star Gazer

Jupiter’s Moons
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