Observing and Imaging Mars

Mars is by far the easiest planet on which the webcam user can record high-contrast detail. But for any imager a good map is essential, and a truly excellent one, aimed at the amateur observer, has been produced by Mario Frassati and Paolo Tanga. Their map is reproduced as Figure 12.1. It shows the planetary features exactly as they appear in a typical amateur telescope, although dust storms can greatly alter the planet's appearance.

Mars is a bright planet; not as bright as Mercury and Venus, but then those inner planets can never be seen as a fully illuminated disc when large, and they do not have the wealth of visible high-contrast surface features the red planet has; at least, not unless you own a spaceship! Mars has an albedo of 16%, which is a vast improvement on our own Moon's reflectivity (7%) and Mercury (6%). In addition, Mars' red color is a huge advantage to the webcam imager. I cannot stress this latter point enough. In typical poor seeing conditions a deep red filter will improve the seeing dramatically. A jittering, juddering image suddenly becomes a slow rippling one. This is of little use though if the object in question has most of its features in the blue end of the spectrum. Fortunately, Mars is at its best (highest contrast surface markings) when seen through a red filter, so a very nice LRGB image (luminance provided by a deep red filter) can be obtained.

Figure 12.1. The excellent Mars map for telescopic observers "Mappa dell Unione Astrofili Italiani" produced by Mario Frassati and Paolo Tanga. By kind permission of Mario Frassati.

For observing visually, a deep red filter such as a Wratten 25A will greatly increase the contrast between dark and light Martian surface features and improve the atmospheric seeing, too. At the other end of the spectrum, a light blue filter, such as a Wratten 80A, will enhance clouds on the Martian limb. Mars is famous for its unpredictable dust storms that can encircle the whole planet at their most energetic. Under such circumstances, all surface markings can be rendered invisible.

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