Moon and Jupiter

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The Moon chases the planet Jupiter across the sky in the wee hours of tomorrow morning. They're in the south at first light, with Jupiter well to the right of the Moon. You can't miss Jupiter because it looks like a brilliant star -- far brighter than any other star-like point of light in the sky.

If we could see Jupiter's magnetic field, the planet wouldn't look like a point at all. Instead, it would look like a long, skinny tadpole, with the tail stretching to the right. The tadpole is a magnetic shield that's deflecting the solar wind -- electrically charged particles from the Sun.

Jupiter's magnetic field is powerful. As the planet rotates, different layers below its surface spin at different rates. These layers are electrically conductive, so they act like an electric motor, creating a "œdynamo" effect that surrounds the planet with a magnetic field.

As the solar wind rams into the magnetic field, it squeezes the front of it toward Jupiter. Some of the solar wind particles are carried down to Jupiter's magnetic poles, where they form aurorae -- like the northern lights here on Earth.

But the magnetic field deflects most of the particles around Jupiter -- like a river current flowing around a small island. Because the solar wind is strong and fast, it sculpts the back end of the magnetic field. So the field forms a long tail that stretches millions of miles into space -- a magnetic tadpole surrounding a giant planet.

Script by Damond Benningfield, Copyright 2008

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