Observing Project 8B Cheshire Polar Caps and Other Atmospheric Phenomena

Mars has a tenuous atmosphere of carbon dioxide that provides less than 1/100th the surface pressure of Earth's atmosphere but that does not mean that Mars' atmosphere is not capable of providing some interesting displays. Even with only 7 millibars of pressure to work with, a good gale force wind can wreak havoc on a surface covered with a lot of loose sand. And on Mars, it often does. Watch for yellow discolorations particularly rising from the northern plains or from large impact basins like Hellas. The polar cap may also disappear into a haze of yellow and red at times. Also watch for the planet's limbs to occasionally become fuzzy and dark instead of sharp and bright. All of these events are signs of dust rising in the atmosphere riding the Martian winds. When Mars is near opposition, particularly when the planet is near perihelion, is when seasoned Mars watchers keep a close watch on the planet's weather. The example of a hide and seek polar cap is just one manifestation of the planet's weather patterns caused by dust rising into the atmosphere. Several locations on Mars are very suspect to dust storm formation, especially the wide-open plains areas.

Polar hoods also tend to form during local winter. These are clouds of ice crystals that form over the poles when large amounts of carbon dioxide sublimate into ice in the upper atmosphere over the polar regions where temperatures during the eleven-month long polar night reach temperatures nearing -170 degrees Celsius. The hoods may grow large enough, particularly during southern winter, which occurs with the planet at aphelion and temperatures in illuminated areas can remain at -50 degrees even at high noon.

Thin wispy cirrus clouds may also form anywhere on the planet, though they are difficult to see. The clouds may be formed either by water vapor (which can be nearly 1% of the Martian atmosphere) or sublimated carbon dioxide in the winter hemisphere. Try using a blue filter to reduce glare and also enhance the white colored clouds against the red surface and see if any of the planet's weather patterns come into view for you. A violet filter will enhance atmospheric features even more but will cause surface features to all but disappear. These high-altitude cirrus clouds are an extreme challenge for amateur size telescopes but the level of satisfaction you will get for bagging them can be just as extreme.

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