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Jupiter and Mars

July 21, 2013

After months of hiding in the Sun’s glare, Mars is finally returning to view. It’s quite low in the eastern sky as twilight begins to paint the dawn. And the planet is easy to find the next few mornings because it has a bright companion: the planet Jupiter.

Both worlds have been passing behind the Sun as seen from Earth. It’s been a couple of months since Jupiter dropped from sight, but five months for Mars. The difference is the motions of the two planets relative to Earth.

Earth is the third planet from the Sun. Mars is the next planet out, followed by Jupiter.

Since Earth is closer to the Sun, it moves faster in its orbit. But Mars isn’t that much farther out, so its orbital speed isn’t that much slower than Earth’s. So as Mars begins to pass behind the Sun, the effect is like two joggers on opposite sides of a track, where one is moving just a little faster than the other. It takes the faster one a long time to notice that she’s gaining on the slower one. Eventually, though, as the distance begins to close, the difference in speed becomes obvious.

Jupiter is three times farther out than Mars is, so it moves much more slowly. That allows Earth to gain ground on it more quickly, so the giant planet soon emerges from the Sun’s glare.

Look for these worlds low in the eastern sky at first light. Jupiter looks like a brilliant star, with fainter Mars close to its upper left. Jupiter will jog past Mars over the next couple of mornings.


Script by Damond Benningfield, Copyright 2013

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