Moon and Jupiter

StarDate: January 17, 2010

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One of the most spectacular sights in the night sky is an aurora -- a colorful, shimmering curtain known as the northern or southern lights. But Earth isn't the only planet with aurorae -- they're also found on the giant planets Saturn and Jupiter. Jupiter's aurorae can be far more powerful than those on Earth -- and some of them are produced in a different way.

On Earth, an aurora forms as our planet's magnetic field directs charged particles from the Sun toward the magnetic poles. These particles strike atoms of gas in the upper atmosphere, knocking off electrons. As the electrons link up with new atoms, the gases in the atmosphere glow.

The same thing happens on Jupiter. But Jupiter's magnetic field is much stronger than Earth's, so its aurorae are up to a thousand times more powerful. They emit much of their energy not as visible light, but as ultraviolet or X-rays.

The X-rays reveal that Jupiter doesn't need the Sun to produce aurorae. That's because Jupiter has another source of charged particles: its volcanic moon Io. The volcanoes blast tons of particles into space. Jupiter's magnetic field funnels them toward the poles, creating a near-constant display of its own northern and southern lights.

Look for Jupiter near the Moon this evening. It looks like a brilliant star to the upper left of the Moon at nightfall. They set by 8 or 9 o'clock. They'll be back tomorrow night, with Jupiter well below the Moon.

Script by Damond Benningfield, Copyright 2009

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

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