More Moon and Jupiter

StarDate: August 6, 2009

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Four hundred years ago this week, Englishman Thomas Harriot drew the first map of the Moon as seen through a telescope. And the Moon looks the same today as it did then. With no air or water to sculpt it, the landscape seldom changes.

But it's a different story for a world that stands next to the Moon tonight: the planet Jupiter. It's the brilliant "star" a little to the right of the Moon at nightfall, and it precedes the Moon across the sky during the night.

The problem with mapping Jupiter is that it's a big ball of gas, so it doesn't have a solid surface. What we see is the planet's turbulent atmosphere, which changes day by day. So mapping Jupiter would be like mapping Earth just by looking at its clouds. You can get a set of daily snapshots, but no long-term map.

There are several large-scale features that remain about the same. Jupiter takes less than 10 hours to turn on its axis. That high-speed rotation stretches Jupiter's clouds into bands that stretch all the way around the planet. The bands form alternating light and dark colors -- the result of air that's either rising or sinking.

And one giant storm system has whirled through Jupiter's atmosphere for many decades, and perhaps centuries -- the Great Red Spot -- a cyclone that's bigger than Earth.

Other than that, though, the details are always changing -- giving mapmakers a pass when it comes to the solar system's largest planet.

Script by Damond Benningfield, Copyright 2009

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

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