Jimmy Westlake: Here comes Mars
January 12, 2010
Steamboat Springs — Get ready. Mars is coming!
You might already have noticed an unusually bright orange star rising in the eastern sky at about 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 during the next few weeks.
As Earth and Mars race around the sun in their orbits, the Earth always has the inside track, so it always is 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 backward 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 also 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 Dec. 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 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 Jan. 27, when the two planets pass within 61.7 million miles of one another. Mars won't be closer than this to Earth until the year 2014. Two nights later, on Jan. 29, Mars will lie in opposition to the sun, rising at sunset, remaining visible all night long, and setting just as the sun rises.
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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 2018.
As if to add an exclamation point to this month's event, on the night of opposition, 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 Feb. 5, Mars passes only 3 degrees from the famous Beehive star cluster.
Use binoculars for the best view.
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. 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 http://www.jwestlake.com.