Sky Watch: Mars in opposition
Now glowing at its brightest, Mars appears against the stars of the constellation Virgo, the maiden, which lie trillions of miles farther than the planet and only appear along the same line of sight.
Mars reaches its official "opposition" on April 8, when the planet lies directly opposite from the sun in our sky. Head outdoors shortly after dark and you'll see what I mean. Stand with your back to the sunset point and there, right in front of you, will glow the brilliant orange light of Mars. You'll have a hard time missing it since it outshines every star in that area of the sky.
Stargazers who keep an eye on the Red Planet over the next few weeks will notice it drifting west through the stars of Virgo -- away from the bright star Spica -- where it will appear to stop its westward motion in late May, turn around and begin heading east. By mid-August, it will enter the constellation of Libra and appear 2.5 times fainter.
To understand why this happens, imagine viewing Earth, Mars and the sun from space. Each day, our planet moves 1.5 million miles along its orbit around the sun. Mars, orbiting farther from the sun's gravitational pull, travels more slowly. This means every 26 months or so, the Earth catches up with Mars from behind, passes it on the "inside," and gradually pulls ahead of it.
You can think of it as two race cars on concentric circular tracks. If the inner car is traveling faster, it will regularly "lap" the outer car and its driver will see the outer car appearing to go backward for a short time.