How to Observe Mars

During most of 2003, as the diagram above indicates, the southern hemisphere of Mars will be tipped toward Earth. For this reason the south polar cap will be quite large and prominent during May and June. But because the season is spring in that Martian hemisphere, observers can expect to see this cap shrink dramatically as it begins to thaw during July and August.

Keep in mind that Mars rotates in the same direction as Earth. So its surface markings move from left to right across the disk if your telescope presents a north-up view that is not mirror-reversed; otherwise they'll move right to left. When comparing what you see to maps like those in this article, you need to know the longitude of Mars's central meridian for the date and time you're observing. You can get this information from our handy Mars Profiler JavaScript, found in the online article "Mars in 2003: Which Side Is Visible?"

Opinions vary as to how large Mars's disk must appear to be studied effectively. For film photographers 10" has been a good rule, but visual observers can glimpse interesting details whenever the disk exceeds 6". CCD detectors are even better at this than the human eye.

But there is another consideration besides the planet’s size for observers living in the Northern Hemisphere. Mars begins May well south of the celestial equator at declination –20°, so it fails to rise more than 30° above the southern horizon (as seen from latitude 40° north). Seeing will suffer, and any crisp markings are likely to be smeared and softened by low-sky haze and turbulence in Earth’s atmosphere. By the end of August it will be getting a little higher each night, but not until mid-December does the planet cross the celestial equator heading north.

Good news for Southern Hemisphere readers: When Mars is nearest Earth in late August, it will pass almost directly overhead in your night sky!

Filters, which are very useful for visual observations of Mars, are now considered almost imperative for digital imaging. Whether you are working visually, with film, or with a CCD, a basic tricolor set of filters is highly recommended. Commonly identified by their Wratten (W) designations, they can be purchased from many telescope dealers and camera stores.

Red or orange filters (W25 or W23A) penetrate Mars’s atmosphere rather handily, exposing such features as the polar caps. They increase the contrast of dark surface markings, and they are best for spotting dust storms. If a patch is bright in red and dim in blue, it's dust.

Green (W58) and blue-green (W64) filters bring out surface fogs, frost patches, and polar-cap extensions.

Blue (W38A or W80A) and violet (W47) filters, because of the Martian atmosphere’s opacity to short wavelengths, are best at highlighting water-vapor clouds and polar hoods. Only in the early stages of the 2003 apparition is there expected to be much cloud activity, however.

Use the filter that provides the highest contrast for the type of feature you are trying to study. Observers with small (3- to 6-inch) telescopes will find that a yellow filter (W15) provides a brighter image and may perform better than a deep-red one. Those doing CCD imaging are forewarned to employ filters that reject infrared light. (The filters currently being sold for this purpose usually do; older photographic filters may not.)

Remember that Mars can always throw in something unexpected. The great dust storm that appeared right around the opposition date in 2001 had not been predicted to happen at all!