No planet goes through more changes than Mars does, and no planet puts our assumptions more to the test. Say its canals don’t really exist. No problem; Mars then offers intriguing dry riverbeds, a strange soil chemistry that spews oxygen at the slightest provocation, and evidence of ancient microbes that may still infect the Red Planet.
Last autumn two American and one Russian spacecraft blasted off to help solve the Martian mysteries. Two are still en route (the Russian craft burned up in our atmosphere), and more will be launched every two years for the foreseeable future.
Why the biennial agenda? Do we synchronize Mars missions with congressional elections?
Actually, the launch windows take advantage of the realignment of Earth and Mars that occurs every 25 or 26 months, offering an opportunity to make a low-energy trip. On those occasions Mars comes closest to us, in a configuration called opposition, since the Red Planet is then opposite the sun in our sky. It happens again this month.
As faster Earth speeds past, Mars seems to slip backward, just as a slower-moving car appears to move backward as you pass it on the highway. While Earth and Mars approach each other, pass, then zip apart, Mars rapidly changes in brightness, offering easy naked-eye and telescope viewing that does not require dark, unpolluted conditions. City skies are just fine.
This month Mars attains a brightness of magnitude -1.3, about the same as Sirius, the night’s brightest star. You can’t confuse the two: the bluish Dog Star rules the southwest at nightfall, while orange Mars rises smack in the east. No other star approaches their brilliance. Nothing could be easier: it’s astronomy for the constellationally challenged.
With vivid, high-contrast viewing provided by Mars’ rust-colored soil, yellow sandstorms, and icy white polar caps, you’d think any telescope would deliver knockout images. But Mars is usually a letdown. The problem: Its small size. Mars’ diameter, 4,217 miles, is only 53 percent that of Earth. Even on March 20, when the planet swells to its maximum diameter (16.3 arc seconds), it’s still just one-third the apparent diameter of Jupiter. You’d need a telescope with more than 150x magnification to reveal surface detail on this disappointingly small disk. But such high power exaggerates the turbulence in our atmosphere, so the result, most nights, is a blurry image; no intrigue, no detail, just a tiny orange pumpkin viewed through boiling water.
Experienced observers--seasoned masochists--compensate by staying at the cold eyepiece for hours, alert for moments when the seeing steadies and Martian detail materializes like a psychedelic hallucination.
If that sounds like work, it’s fun simply to follow the changing pattern of Martian oppositions. Because Mars’ orbit is quite elliptical, the gulf between us at opposition can be relatively small (as in 2001 and 2003, when just 40 million miles or less separates us), or large, as it is now. Our current meeting, 61.3 million miles apart, is almost as distant as possible.
But optimists might point out that now, for the last time until 2005, the Northern Hemisphere is tilted toward Mars when we rendezvous. The Red Planet is prominent for all North American and European observers, and climbs fairly high, reducing atmospheric turbulence. The next three oppositions will find Mars larger and brighter, but low (in 1999), ridiculously, horizon-huggingly low (in 2001), and quite low (in 2003).
So all eyes look to the Virgo-Leo boundary, where Mars reigns as the brightest star of the midnight sky.