Making the Most of Mars

Making the Most of Mars

From Earth’s point of view, Mars is unique. It’s the most Earthlike world we know; backyard telescopes can sometimes show polar caps, surface markings, seasonal white clouds, and windblown dust. Mars also behaves uniquely in our sky. It spends most of its time far away as a tiny blob in a telescope, then every 2.1 years it swings much closer for just a few months around opposition.

Moreover, Mars comes almost twice as close at some oppositions than at others (because Mars has a significantly elliptical orbit that is also near Earth’s orbit). The near and far oppositions (“perihelic” and “aphelic”) come and go in a 16-year cycle.

We’re now near the bottom of that cycle. Mars reaches opposition and makes its closest approach to Earth in late January 2010. But it appears only 14.1 arcseconds in diameter at the time. Mars will appear larger than 12″ through the end of February, and larger than 10″ through late March (see the graph on the bottom). That’s pretty small.

And next time around, in March 2012, Mars will be only 13.9″ wide at closest approach. Not until July 2018 will it peak out again, at 24.3″.

But astronomy is all about making the most of very distant, difficult views. And at least Mars will cross the night sky high for Northern Hemisphere observers. It spends the next five months in and near Cancer, at declinations +16° to +23°.

In a good 4-inch or larger telescope on a night of steady air, you may first make out the bright north polar cap. In February or March you may notice the cap shrinking in the Martian northern spring. Dark surface markings may be harder to discern, depending on which side of Mars is facing Earth when you look. Watch also for bright limb hazes, occasional white clouds, and possibly the obscuring bright patch of a dust storm moving from day to day. But don’t expect impressive views. Every bit of what you see will be a hard-won prize.