It was nearly four centuries ago that the great Italian astronomer Galileo Galilei first aimed his telescope toward the heavens. Over time his new optical tube revealed to him mountains, valleys and craters on the moon, spots on the sun and the phases of Venus. But when he aimed his instrument in the direction of Jupiter, he received the shock of his life.

Through his tube the planet appeared different than the stars — it was a small round disk with two bright points of light to the planet's east and one to its west.

The following night he looked again, but something was different. The three tiny stars were not where they were the night before. Now they all appeared to the planet's west. If Jupiter had moved past them as it orbited the sun, he reasoned, then it didn't behave as astronomers had predicted. He was anxious to see what would happen next.

After a night of clouds he looked again. Now he saw only two stars, and both were to the planet's east. Was he going mad? Was Jupiter swinging like a pendulum in front of the distant stars? Or was something else happening?

Night after night he watched the show, never quite knowing what to expect. Then, a few nights later, he no longer saw three stars. Now there were four — one to the planet's east, the others to its west.

Galileo now was positive that these intriguing lights weren't distant stars at all, but rather moons that orbited their parent planet. And he knew that these observations proved definitively that the Earth could not be the center of the universe, for here was a system in which bodies orbited another planet.

This week, brilliant Jupiter shines low in the southern sky just after dark, and provides us an opportunity to aim a small telescope in its direction to repeat Galileo's amazing discoveries.

Now known as the four Galilean satellites — Io, Europa, Ganymede and Callisto — provide endless entertainment for the backyard astronomer. You can identify them by visiting www.shallowsky.com/jupiter.html and entering the date and time. And to learn more about these incredible moons and their amazing parent planet, be sure to check out: www.nineplanets.org/jupiter.html.

Today, we know that the great, gaseous planet Jupiter is orbited by more than five dozen moons. Wouldn't Galileo be surprised and thrilled!

To find out more about Dennis Mammana and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at www.creators.com.

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