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by Damond Benningfield

The last time Earth and Mars passed this close to each other -- well, almost this close -- a Northeastern astronomer launched a nationwide effort to listen for Martian radio broadcasts. The time before that, Giovanni Schiaparelli saw a series of dark markings on the planet's surface that some interpreted as canals built by an ancient civilization.

Expectations are a bit lower for this summer's close passage -- at least those of professional scientists. With two spacecraft orbiting the planet, they're seeing dazzlingly clear views of Mars every day. And probably for the first time since the invention of the telescope, few of their ground-based instruments will watch the planet.

For most amateur astronomers and casual skywatchers, though, Mars will be the center of attention. At 4:51 a.m. CDT on August 27, 2003, Earth and Mars will pass just 34,646,437 miles (55,758,006 km) from each other, says E. Myles Standish, an astronomer at the Jet Propulsion who plots the precise positions of the planets for spacecraft navigators. (The number is accurate to "maybe 10 to 20 meters," Standish says.)

Mars will look like a brilliant reddish-orange star, outshining every other planet and star visible during late August.

Even better, this close encounter occurs just one day before Mars reaches opposition, when it stands opposite the Sun in our sky, so it rises at sunset and remains visible throughout the night.

This impressive lineup is the result of an astronomical coincidence.

"I think of Earth and Mars going around the Sun like two cars going around a race track," says Standish. Earth is closer to the Sun, so it moves faster on its inside lane, overtaking Mars every 26 months.

But the geometry of each encounter is different. Mars' orbit is more lopsided than Earth's, so its distance from the Sun varies by about 27 million miles. The best oppositions occur when Earth passes Mars near the Red Planet's closest approach to the Sun, called perihelion, which this year occurs on August 30. What's more, although Earth's orbit is less lopsided than Mars', our planet was farthest from the Sun in early July, further reducing the distance.

One astronomer calculated that this encounter is the closest between Earth and Mars in almost 60,000 years. "I have a lot of confidence in that result," says Standish. "I haven't had time to run the numbers myself because we have spacecraft going to Mars and we need to know where it is now -- and not just approximately."

Standish and others, however, point out that the difference between this and other "perihelic oppositions" isn't all that much -- often less than one percent. Other good oppositions took place as recently as 1988 and 1971. To the unaided eye, this opposition won't look any better, says Standish.

The best opposition of the 20th century was in 1924, when Mars passed just a few thousand miles farther than it will this year. David Todd, a former chairman of the Amherst College astronomy program, thought the close approach presented a good chance to listen for Martian radio signals. He convinced the United States Navy and War departments, a Washington radio station, and others to join the search, but no Martians called in.

One of the best oppositions of the previous century came in 1877, when Schiaparelli mapped a series of thin, dark lines on the planet's surface. American astronomer Percival Lowell interpreted these markings as canals built by a dying civilization, and built his own observatory to study them. The idea of Martian canals persisted until the first spacecraft flew past Mars in 1965.

Many planetary astronomers will sit this one out, though. "Mars science is moving into the realm of spacecraft geology and meteorology," says Ed Barker, assistant director of McDonald Observatory, who until this year had been observing Mars regularly since 1965. "The spacecraft imagery has so much more detail than we could ever get from the ground. You can see landslides and dust devils and other activity. There's no way we can ever get that [from Earth], even with Hubble."

Still, scientists like to see global coverage of the planet -- not just the details. "There's weather on Mars, and it's not the same every year," Barker says. "We get such close-up pictures from the spacecraft now that we're not looking at the overall global meteorology." Hubble Space Telescope will snap some global images at different seasons, but Barker says that amateurs are helping the professionals by keeping an almost round-the-clock watch on Mars.

While this opposition may not produce any great discoveries -- real or imagined -- it's still fun to look at, Barker says. "I've got grandkids to look at Mars with now, so I'll probably go out and buy a telescope."