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Mars and Regulus

November 10, 2011

Mars sweeps past an old friend the next few mornings: Regulus, the brightest star of Leo, the lion. They rise not long after midnight and are high in the southeast at first light. Mars looks like a bright orange star. Fainter Regulus is a little to the right or lower right of Mars.

The two bodies are like old friends because Mars periodically moves past the bright star.

Regulus lies quite close to the Sun’s path across the sky. Mars also stays close to this path as it circles against the background of stars once every couple of years.

The planet’s motion across the sky isn’t a one-way street, though. Instead, Mars periodically reverses direction. It’s not that Mars itself is changing course, only that it looks like it is — a result of the changing angle between Mars and Earth.

It’s like watching a car cruise along the highway in a parallel lane. When it’s ahead of you, it appears to be moving forward against the background of buildings or trees. As you get closer to the car and then pass it by, it briefly appears to be moving backward against that same background. The car is still moving forward, but because you’re passing it, your viewing angle is changing.

And that’s just what happens with Mars. It’ll reverse directions across the sky in January. We’ll pass by the planet in March, and it’ll resume its normal eastward motion in April.

For now, look for Mars huddling close to Regulus, high in the sky at first light.


Script by Damond Benningfield, Copyright 2011


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