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One of the moons of Saturn seems to be stuck in the 1950s. Like popular shoes and cars of that era, it's two-toned -- bright on one side, dark on the other.

The moon is Iapetus -- a ball of rock and ice that's less than half the size of our own moon, and more than two million miles from Saturn.

The most striking thing about Iapetus is its color scheme. The hemisphere that faces forward as it orbits Saturn is as dark as coal, while the other hemisphere is as bright as new-fallen snow. This two-toned scheme may be the result of a two-step process.

The leading hemisphere is coated with a thin layer of dark material. This may be dust blasted off the surfaces of some of Saturn's other moons by impacts with chunks of rock and ice. The material flies into space, and Iapetus sweeps up some of it as it orbits Saturn.

The dark coating absorbs sunlight, so it warms the ice below it. A recent study says that some of the ice vaporizes. The water vapor drifts around Iapetus, and condenses when it reaches the colder trailing hemisphere. That makes the white side even whiter, and the dark side even darker -- leaving this two-toned moon stuck with a bygone fashion.

Saturn teams up with our own moon this evening. At nightfall, Saturn and Mars stand close to the right of the crescent Moon. Saturn is brighter and a little closer to the Moon. Regulus, the brightest star of Leo, completes the array, to the lower right of the planets.

Script by Damond Benningfield, Copyright 2008

For more skywatching tips, astronomy news, and much more, read StarDate magazine.