Mars bright in evening sky

Many of us may remember a claim from early last summer that the planet Mars and Earth would come within close proximity to each other by August. The story was sensationalized by suggesting that at closest approach Mars may appear as large as the moon.

Shocking as it may seem (it was on the Internet; how could it not be true?), the event didn't happen! Not only did Mars not show prominently, it was completely absent from the evening sky, instead being very far from Earth and only dimly visible in the early morning. And as for its size, Earth's second-nearest planetary neighbor can never appear larger than a point of light to the naked eye.

But the Red Planet is making a return to the evening sky this winter. Earth has been gradually catching up to the slower-moving Mars, and on January 29 it will move to a position directly between the sun and Mars. This planetary configuration is called opposition. At that time, Earth and Mars will be separated by less than 62 million miles - significantly farther than in August, 2003, when the two planets were just 34 million miles apart.

Still, Mars will dominate the evening sky, as its orange hue will outshine all the other stars except Sirius, located low in the south. As night falls, Mars will rise in the east and be visible all night long. Through late winter and into spring, the gradually fading beacon will rise earlier each evening as the two planets begin to pull away from each other. Mars will spend most of this time in the inconspicuous constellation of Cancer, situated between the more prominent star patterns of Gemini and Leo.

The timing between oppositions and the large disparity between close approaches of Mars is governed by celestial mechanics. Because the orbit of Mars lies beyond that of Earth's, it takes the Red Planet about 322 days longer to complete one revolution of the sun as it does for Earth.

Suppose the sun, Earth and Mars are in a straight line, with the two planets on the same side of the sun (opposition.) It will take 26 months until the two planets and sun are once again in the same sort of alignment.

If the orbits of Earth and Mars were perfect circles, the distance of closest approach would always be the same. Their paths through space, however, are not circles but ellipses, and Mars' orbit is significantly more out-of-round than Earth's. As a result, the separation between the two orbits varies considerably. When opposition occurs near minimum separation, the planets are relatively close together. The reverse is true when this planetary configuration happens where the orbits are farthest apart.

Although the 2010 opposition isn't a particularly favorable one, amateur star gazers who have access to a six-inch or larger telescope stand a chance of detecting markings on the planet. These features may include the shrinking north polar ice cap and some of the larger dark regions on the planet's surface.

But it won't be easy. Even a properly focused telescopic image will blur, sharpen and blur again in a matter of just a second or two because of turbulence in Earth's atmosphere. An experienced observer learns that a prolonged sharp image is exceedingly rare, and that seeing detail is best accomplished during the fleeting moments when the image is clearest. It can be done with a little practice. Give it a try if you have the opportunity.

I will not be surprised if the Mars hoax resurfaces again this summer. But if it does, you will immediately dismiss it, because you know that Earth won't catch up to Mars again until March of 2012.