By Jimmy Westlake, professor of physical science, Alpine Campus
You might have already noticed an unusually bright orange star rising in the eastern sky around 9 p.m. That’s no star at all; it’s the Red Planet, Mars, and it’s going to be getting even brighter in our sky over the next few weeks. Here’s why:
As Earth and Mars race around the sun in their orbits, the Earth always has the inside track, so, it is always moving faster than Mars. Consequently, the Earth catches up with Mars from behind and passes it about every 2.1 years. As viewed from Earth, Mars seems to move backwards in the sky against the background stars during the few weeks that we are passing it.
This peculiar backwards, or, retrograde, motion was very difficult for ancient sky watchers to explain because they held firm to the belief that the Earth was motionless and at the center of the universe. Indeed, if one clings to that belief, it is most difficult to explain how a planet can appear to stop, back up in the sky for a few weeks, and then take back off again like nothing ever happened. The ancient Greeks devised a complicated system of circles whirling in circles in an attempt to explain it, but, all of that became ancient history once we realized that the Earth, too, is in motion around the sun. Whenever Earth gains a lap on one of the outer planets, that planet presents the illusion of reversing direction against the starry background.
On December 20, Mars began backtracking through the stars of the constellation Leo and will enter the constellation of Cancer the Crab before resuming its forward motion again on March 10. In the middle of that 11-week stretch, Earth will be as close to Mars as it can be for this cycle. The night of closest approach will be January 27 when the two planets pass within 61.7-million miles of each other. Mars won’t be closer than this to Earth until the year 2014. Two nights later, on January 29, Mars will lie in opposition to the Sun, rising at sunset, remaining visible all night long, and setting just as the Sun rises.
This year’s opposition of Mars is not a favorable one. Because of Mars’ elliptical orbit, it can come as close as 35-million miles at a favorable opposition or as far as 63-million miles at an unfavorable opposition. The next favorable opposition of Mars won’t happen until the year 2018.
As if to add an exclamation point to this month’s event, on the night of opposition, January 29, the full Snow Moon and Mars will rise together in the east-northeast, side by side, providing an unforgettable cosmic moment. The moon and Mars will glide together across the sky all night that night, less than a fist-width apart. A week later, on the night of February 5, Mars passes only 3 degrees from the famous Beehive star cluster.
Use binoculars for the best view.
Professor Jimmy Westlake teaches astronomy and physics at Colorado Mountain College’s Alpine Campus. He is an avid astronomer whose photographs and articles have been published all around the world. His “Celestial News” column appears weekly in the Steamboat Today newspaper and his “Cosmic Moment” radio spots can be heard on local radio station KFMU. For a full-color calendar of celestial events in 2010 featuring some of Jimmy’s best astrophotos, check out “Jimmy’s 2010 Cosmic Calendar” at his Web site.