Venus and Mercury

StarDate: March 31, 2010

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In the entire universe, there are only two planets that we look inward to see: Venus and Mercury. Their orbits are closer to the Sun than Earth's is. All the other planets in the solar system -- and the hundreds discovered beyond the solar system -- are outside Earth's orbit.

And as it happens, Venus and Mercury will be huddling close together for the next couple of weeks. They're quite low in the west at sunset, and set about an hour and a half later. But if you have a clear horizon, you should be able to pick them out, because Venus is the brightest object in the night sky after the Moon.

Mercury is the closest planet to the Sun -- an average of about 40 percent of Earth's distance from the Sun. It's a bare chunk of rock that's not that much bigger than the Moon. It has no atmosphere to speak of, so it's scorched by the full power of the unfiltered Sun. Peak temperatures at the equator top 700 degrees Fahrenheit.

Venus is the next planet out -- about three-quarters of the way out to Earth's orbit. It's almost as big as Earth, and it's surrounded by a thick, toxic atmosphere. The air traps the Sun's energy, heating the surface to 850 degrees.

Look for scorching Venus -- the beautiful "evening star" -- quite low in the west beginning about 30 minutes after sunset. Mercury is a little to its lower right. It's much fainter than Venus, but with Venus as a guidepost, you should be able to pluck it from the fading twilight.

Script by Damond Benningfield, Copyright 2010

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

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