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Mercury, July/August 2003 Table of Contents

by Daniel P. Joyce and Daniel M. Troiani

In late August, Mars will come as close to Earth as it ever gets. Even modest telescopes will reveal a fascinating wealth of detail.

Courtesy of Daniel M. Troiani

With a diameter only 53% that of Earth's, Mars is a small planet. Because of its small size, experienced observers can discern impressive detail on Mars only when it comes close to Earth. On August 27 of this year, Mars will come closer to Earth than it has at any time in the past 59,540 years. Now that it is as close as it ever gets, even inexperienced observers using small telescopes will be able to see intricate details.

These details include features that make Mars more Earth-like than any other body in the solar system in virtually every category except for size and mass. Mars has changing weather patterns, with haze, water ice clouds, and ground fog. It has dark markings that change in size and color. It has polar caps. You can even see changing seasonal effects that result from its 25° axial tilt.

On the down side, Mars also experiences dust storms. Fortunately, these storms are usually just local events. But occasionally they can grow large enough to envelop the entire planet. Global dust storms are rare enough that it is unlikely one will occur during this year’s apparition. But during Mars’s last close approach in June 2001, several regional dust storms converged to form a single giant dust storm that covered the entire surface except for the polar regions.

With its many changing phenomena, Mars will appear different almost every time an observer looks through a telescope. This is a once-in-a-lifetime opportunity, so try to observe Mars as often as possible this summer. Sure enough, the one night you decide to stay indoors and watch TV will be the night a major event will happen on Mars.