Moon and Jupiter

StarDate: July 31, 2010

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The Moon and the planet Jupiter highlight the sky late tonight. They rise in late evening, with Jupiter to the right of the Moon. Jupiter outshines all the other planets and stars in the sky at that hour, so you can't miss it.

One reason Jupiter looks so bright is because bright clouds top its thick atmosphere. They reflect about half the sunlight that strikes them.

The Moon, on the other hand, is quite dark. The lunar surface is made of rock and dust that reflect only about one-tenth of the sunlight that strikes them.

Moon dust is fine and powdery. It's churned up when space rocks slam into the surface. And energy from the Sun creates an electric charge that appears to "levitate" some of the dust into the airless lunar sky.

Some of the dust may settle on reflectors left on the lunar surface by Apollo astronauts. Scientists bounce laser beams off the reflectors to measure the precise distance between the Moon and Earth. They're using the observations to test Albert Einstein's theory of gravity, and to measure the structure of the Moon's interior.

But the reflection isn't as bright as it used to be. Scientists have concluded that a thin layer of dust partially coats the reflectors, blocking some of the light. The dust also changes the temperature of the glass cubes that make up the reflectors, which further dims the signal.

The reflectors are still getting the job done, but the dust makes the job just that much harder.

Script by Damond Benningfield, Copyright 2010

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

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