The Pull of Jupiter

The giant planet is having a close encounter with Earth all month long. On May 6th, the date of closest approach, Jupiter will be 410 million miles away, which is almost 200 million miles closer than it was just six months ago in October. This makes Jupiter unusually big and bright.

Look for it rising in the east at sunset. Jupiter is unmistakable, shining ten times brighter than any star around it. The view through a backyard telescope is dynamite. You can see Jupiter's cloud belts, the Great Red Spot and four large moons (Io, Europa, Ganymede and Callisto) circling the planet.

Above: Jupiter and Ganymede photographed by amateur astronomer Alan Friedman of Buffalo, NY, using his 10-inch telescope.

When you look at Jupiter through a telescope, you might notice something odd: the planet looks squashed. Your eyes are okay. Jupiter truly bulges around the middle because it spins so fast. One complete turn of the planet takes only 10 hours. That's more than 300 Earth masses (almost enough to make a star) spinning like a nimble asteroid.

This spinning allows you to see the entire planet in a single night. On May 6th, Jupiter is "up" for more than 10 hours, or one complete turn. Judo astronomers will attempt a Jupiter marathon: In 10 hours you can see the innermost moons of Jupiter move from one side of the planet to the other. You can watch the Great Red Spot, a hurricane twice as wide as Earth, churn across Jupiter's cloudtops. You might even see "Red Jr.," a baby Great Red Spot trailing the original by about 2 hours: full story.

Although closest approach is May 6th, the best night to look is May 11th when the full Moon and Jupiter appear side by side. The pair will rise in tandem at sunset and remain beautifully close together all night long. With a telescope you can quickly scan back and forth: The lunar Alps. The moons of Jupiter. The Sea of Tranquillity. The Great Red Spot.

Do you feel the pull yet?

Let's calculate: Jupiter is 318 times more massive than Earth and 410 million miles away. According to Newton's Law of Universal Gravitation, Jupiter pulls you up 34 million times less than Earth pulls you down. Jupiter's "pull" is utterly feeble.

So it's all in your mind. But don't let that stop you: give in to the pull!

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Author: Dr. Tony Phillips | Production Editor: Dr. Tony Phillips | Credit: Science@NASA

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