Moon and Venus

StarDate: September 14, 2009

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[audio: rooster crowing]

Venus would probably be a pretty dull place for a rooster. He'd get to crow just twice a Venus year, because a Venus day lasts the equivalent of about four months here on Earth.

In many ways, Venus and Earth are alike. The planets are about the same size and mass, for example. And Venus is the second planet from the Sun, while Earth is third.

In other ways, though, they're quite different. Venus is bone dry, and its surface is hot enough to melt lead; more about that tomorrow.

Another difference is the way they rotate. Earth turns so fast that the Sun returns to the same point in the sky once every 24 hours. On Venus, though, it takes 117 days.

What's more, Venus turns backwards compared to Earth and most of the other planets. As seen from above the Sun's north pole, Earth turns counterclockwise. But Venus turns clockwise, so the Sun rises in the west and sets in the east.

The leading explanation for the difference is that Venus got whacked by another planet-sized body early in its history. The collision flipped Venus upside down.

Earth got whacked, too, but with different results. The collision vaporized Earth's outer layers, spewing them into space. The material quickly cooled and coalesced to form the Moon -- one more difference between Earth and our neighbor world.

Look for Venus and the Moon at first light tomorrow. Venus is the brilliant "morning star" to the lower left of the Moon.

Script by Damond Benningfield, Copyright 2009

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

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