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Loopy Planet

April 27, 2014

The planet Mars is a bit “loopy” right now. It’s making a loop against the background of stars — the result of Mars’s retrograde motion across the sky.

Most of the time, Mars and the other planets move eastward against the stellar background — the result of their orbital motion around the Sun. Sometimes, though, a planet reverses direction for a while. Its orbital motion is the same — the only change is our viewing angle.

Mars goes into retrograde when Earth passes by it in our smaller, faster orbit around the Sun. It’s like one car passing another on the highway. Seen from the faster car, a vehicle ahead of it seems to be moving forward against the background of buildings and trees. As the faster car passes it, though, the other one briefly appears to be moving backward against the background. It’s not, though — it’s just a matter of perspective.

Earth passed Mars earlier this month, so the Red Planet will move “backwards” for a few more weeks. Many take that as a sign that they need to alter their behavior, or that big things are going to happen — good or bad. But the idea that a change in any planet’s motion across the sky has an effect on daily life is just plain loopy.

Brilliant orange Mars is high in the southeast at nightfall. Spica, the brightest star of Virgo, is close to its lower left. Mars is moving away from Spica right now, but will soon head toward the star as it completes its loop and resumes its normal motion across the sky.


Script by Damond Benningfield, Copyright 2014

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