Brilliant Venus

StarDate: May 2, 2009

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The planet Venus reigns as the "morning star" this month. And for the next few days it has an extra luster to it -- it's at its brightest.

Venus's brightness changes for several reasons.

For one, its distance from Earth changes -- from as close as 27 million miles, to as far as 160 million miles. Right now, it's on the closer end of the scale. In fact, it was closest just a few weeks ago, when it crossed between Earth and the Sun.

And for another, the planet goes through a cycle of phases, just as the Moon does. It's a fairly thin crescent now, so only a small portion of its sunlit dayside faces our way. Most of what we see is actually the dark nightside.

You might expect the planet to be faintest when it's a crescent, just as a crescent Moon is fainter than a full Moon. But that's where the closeness comes in.

Since Venus is quite close right now, it's quite large in our sky. The crescent covers more area than an almost-full Venus does, because when it's close to full, the planet is on the opposite side of the Sun -- millions of miles farther than it is now.

What's more, each square foot of Venus reflects far more light toward Earth now than when the planet is on the opposite side of the Sun.

So when you add them up, Venus puts on its best showing when it's a fairly thin crescent, as it is now.

Look for Venus in the east beginning a couple of hours before sunrise. It'll remain perched in the morning sky through the end of the year.

Script by Damond Benningfield, Copyright 2009

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