Observing Jupiter

Only Venus is brighter than Jupiter, and, since Venus cannot appear in the midnight sky, Jupiter reigns supreme as the Lord of the Night, brighter than any star.

Any low power telescope (15 - 50 power)will show the four large moons of Jupiter. You can even see them in seven or higher power binoculars. Hold the binoculars stably, resting your elbows on a support and focus carefully. Sometimes one or more of the moons is in front or behind the planet, or too close to the planet to easily see.

At higher power, 100 - 200 X, there is more to see. The face of the planet has cloud bands running horizontally. The Great Red Spot, a gigantic storm, can often be seen. Jupiter rotates rapidly, making a revolution in only about ten hours, so if you watch the Red Spot over an hour or two, you can see the movement. Of course, the Red Spot may be on the back side of the planet and not visible at the time when you are looking. The rapid rotation also gives Jupiter a squashed, oblate shape, which is visible at these powers.

The moons, too, do interesting things that are visible at higher power. The most easily visible event is a shadow transit, where the shadow of a moon moves across Jupiter's face. It is more difficult to see the moon itself against Jupiter's bright surface. Jupiter's shadow may extend out beyond the surface of the planet, especially near times of quadrature, about three months before or after opposition. Then you may see a moon disappear into the shadow some distance from the disk, and later reappear closer to the disk, only to disappear behind the disk itself.

The moons have periods of revolution from about one and a half days to sixteen days, so events of this sort are occuring off and on all the time. You can find lists and diagrams of predicted events in Sky and Telescope and Astronomy magazine.

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