Double Double 
The southwestern quadrant of the sky offers up a double skywatching treat this evening: a close pairing of two planets, and an even closer pairing of the Moon and a bright star.
The most obvious double is the Moon and Antares, the bright orange star that marks the heart of Scorpius. If you're on the East Coast, they'll be separated by less than a degree as the sky begins to darken -- less than the width of a finger held at arm's length. They'll be a little farther apart from more westerly locations, but they'll still form a tight, beautiful pair.
The other double is the planets Venus and Mars, low in the southwest at nightfall. Venus is the brighter of the two; it's the brilliant "evening star," so you just can't miss it. You can't miss Mars right now, either, because the Red Planet stands almost directly above Venus.
Mars looks less than one percent as bright as Venus does. That's because Mars is smaller and much farther away than Venus is, and because its surface reflects much less sunlight. Venus is one of the most reflective objects in the solar system -- its clouds bounce two-thirds of the sunlight that strikes them back into space. By contrast, Mars reflects less than one-sixth of the sunlight that strikes its surface.
Despite the contrast, though -- or perhaps because of it -- Venus and Mars form a beautiful duo, shining in the western sky at nightfall and through much of the evening.
Script by Damond Benningfield, Copyright 2010.