More Moon, Mars, and Gemini

StarDate: October 11, 2009

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A beautiful astronomical array decorates the eastern sky early tomorrow: the Moon, the planet Mars, and the twin stars of Gemini. They rise in the wee hours of the morning, and stand high in the sky at first light.

The Moon, of course, is our closest celestial neighbor. It's just a quarter-million miles away -- a distance that changes very little.

And right now, Mars is our fourth-closest neighbor. But the distance to Mars varies by quite a bit. Right now, it's about 125 million miles, but it's closing fast. In late January, Mars will be just half that far.

The distance is changing because Earth is about to overtake Mars in our smaller, faster orbit around the Sun. Earth is the third planet out from the Sun, while Mars is fourth. The distance between the planets is greatest when they're on opposite sides of the Sun, and smallest when they line up on the same side of the Sun.

And that's what's happening now. Earth is catching up to Mars, and will pass it by in late January. When that happens, the two worlds will be just 62 million miles apart, so Mars will shine a good bit brighter than it does tonight.

For now, look for Mars almost directly above the Moon as they rise late tonight. It looks like a bright orange star. The true stars Pollux and Castor -- the twins of Gemini -- line up above Mars -- many light-years beyond our solar system neighbors.

We'll talk about two more of those neighbors tomorrow.

Script by Damond Benningfield, Copyright 2009

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

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