Mars and Saturn

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Two planets are crossing paths this week -- Mars is climbing past Saturn. They're in the west at nightfall, and look like fairly bright stars. They're stacked atop one another tonight, but Mars will soon move past its sister planet.

Although they look like similar pinpoints of light, Mars and Saturn are quite different.

Mars is made of rock and metal, like Earth is, although it's only about half as big as Earth. Its surface looks a lot like Earth's deserts, with giant mountains and canyons, rippling dunes, and vast plains coated with orange dust. Some of the dust gets pulled into twisting vortexes of air, forming dust devils that can rise thousands of feet into the sky. Dust that's suspended in the air colors the daytime sky in shades of pink and yellow.

Saturn, on the other hand, is a ball of gas surrounding a rocky core. It's almost 10 times Earth's diameter. Most of the planet consists of hydrogen and helium, either as a gas or squeezed so tightly that it forms a metal. It's topped by bright clouds that are colored subtle shades of yellow and tan by ammonia and other chemical compounds. And most strikingly, Saturn is encircled by beautiful rings.

Look for Saturn and Mars low in the west as twilight fades away. Brighter Saturn stands just above Mars, by about the width of a pencil held at arm's length. The true star Regulus adds to the drama, to the lower right of the planets.

More about Mars and Saturn tomorrow.

Script by Damond Benningfield, Copyright 2008

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