Mars, Here We Come!

11. Observing Mars This Year

Approximately every 26 months, Mars comes to opposition. This is when the bodies Sun-Earth-Mars lie in a straight line (with the Earth in the middle) and is the time when Mars is closest to Earth. Therefore, this is when Mars appears to be its brightest and largest. Opposition this year occurs on April 24, 1999 and Mars is at its closest on May 1, 1999 when it is at a distance of 54 million miles.

Mars is hard to see in any detail, except at opposition. Even then, fine detail may be difficult to see. The nearness of Mars at opposition goes through a 15 year cycle. We are currently in the upswing of such a cycle. This year, Mars reaches a largest apparent size of 16.2 arcseconds in diameter (the best opposition of this cycle occurs on August 27, 2003 when it will have an apparent diameter of 25 arcseconds). Here is a graph of the apparent size and magnitude of Mars this year (from Sky and Telescope, April 1999):

It takes a lot of patience to see detail on Mars. The quality of image is affected by the stillness of Earth's atmosphere, the altitude of Mars in the sky, and the activity in Mars' atmosphere (namely, clouds and dust storms). The best way to observe Mars is to watch for long periods of time while you wait for a glimpse through steady air. Through an 8 inch telescope (such as those here at the ETSU observatory), you should expect to see dark surface markings and the north polar cap. You might also see limb haze and occasional white clouds or dust storms. Here's a map of the features visible through a small telescope (from Sky and Telescope, April 1999):


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