Jimmy Westlake: Earth passes Mars this week
February 28, 2012
Steamboat Springs — Once every 780 days, Earth passes in between Mars and the sun, placing the two planets as close together as possible. This alignment of worlds is called opposition. When Mars reaches opposition on March 3, it will be 63 million miles from Earth, its closest point for 2012. Mars will be shining prominently in the constellation of Leo, not far from the bright star Regulus.
Because of the elliptical shape of Mars' orbit, some oppositions are closer than others. This year, when the Earth swings past Mars, Mars will be near its farthest point from the sun, a state called aphelion. Such "unfavorable" oppositions recur in a 15-year cycle. "Favorable" oppositions occur when Earth passes Mars while the red planet is near its closest point to the sun, called perihelion. The next favorable opposition of Mars won't happen until 2018, when it will be only 36 million miles from Earth.
On the night of opposition, dazzling red Mars will rise in the eastern sky at sunset while three of the four remaining naked-eye planets and the moon share the stage. Turn your back on Mars and look west as the sunset glow fades from the sky. There, you will see the twin beacons of Venus and Jupiter lighting up the night. Venus is the brighter of the two. Below them and closer to the horizon, you also might spot the elusive planet Mercury until about 7:30 p.m. Overhead, the 10-day-old moon will shine down brightly.
Draw an imaginary line in the sky connecting these celestial dots — Mercury, Venus, Jupiter, the moon and Mars — and you will have traced out the ecliptic, the heavenly highway that the sun, moon and planets follow across our sky. Watch Mars in the next several weeks as it closes in on Leo's brightest star, Regulus. It stops just short of the star on April 11, then begins backing away from it again.
While we ogle Mars in our evening sky this week from our earthbound vantage point, NASA's Mars Science Laboratory is speeding faster than a bullet toward its rendezvous with the red planet next August. Once there, it will drop the Curiosity rover into the Gale Crater, where it will scratch and sniff for signs of past Martian life. Curiosity will roam the red sands of Mars for many months, beaming back pictures and data that will keep planetary scientists busy for years to come.
Through a medium-sized backyard telescope, Mars looks like an orange ball. If the air is steady, you might catch a glimpse of Mars' white polar ice cap, gleaming in the sunlight, and maybe a hint of some dark features on the Martian deserts. You don't need a telescope at all, however, to enjoy watching our neighboring world as we swing by it this week.
Jimmy Westlake teaches astronomy and physics at Colorado Mountain College's Alpine Campus. Check out Jimmy's astrophotography website at http://www.jwestlake.com.