Guest Author - Lea Terry

Mars is going retrograde. No, that doesn’t mean it’s going to start wearing bell bottoms or unpack the lava lamps; it means the Red Planet will appear to move backward through the sky as it moves closer to Earth.

Mars - “The Wandering Star”

Nicknamed “the wandering star” by ancient cultures, Mars is not the only planet to behave so strangely--all planets exhibit retrograde motion during their trek around the Sun. But when Mars goes retrograde, it will also appear to move slightly above the path it normally follows.

Mars has been moving closer to Earth, in an eastward direction, since the beginning of the year, starting out at 221 million miles away. This week it is only 63 million miles from Earth, and shines 10 times brighter than it did in early 2007. For several weeks, Mars’ motion has also appeared to slow, and on Nov. 15, will appear to stop. Then it will appear to reverse its course, moving westward until Jan. 30, 2008, when it will again appear to stop and reverse direction, this time returning to its eastward path.

The Mystery of Retrograde Motion

Retrograde motion wasn’t understood until 1543, with the publication of “De revolutionibus" by Nicolaus Copernicus. Before Copernicus explained the retrograde mystery, astronomers struggled to reconcile this baffling behavior with their long-held models of the solar system. (Their models, as it turns out, were incorrect.) Early astronomers believed that the planets, the Sun and the Moon all moved in perfect circles around the Earth. But this didn’t allow for the backward motion. The ancient Greeks proposed an explanation: they said the planets moved in small circles, called epicycles, while they traveled around the Earth. However, even this explanation didn’t match the observed behavior of the planets. Copernicus, though, unraveled the mystery by putting the Sun, instead of the Earth, at the center of the solar system. The backward motion, it is now known, is simply an optical illusion. Because both Earth and Mars are traveling in the same direction, but Mars is moving more slowly, Mars appears to move backward in relation to Earth.

Observing Mars

This will be the best view of Mars until 2016, and it’s best seen in late evening, in the east-northeast part of the sky. Just look for the yellow-orange “star”-like body.