Introduction Mars, the fourth planet in order of increasing distance from the sun and the first beyond the earth’s orbit. Under favorable conditions, it appears in the night sky as a yellowish red object (hence the name “red planet”) of the first magnitude. Mars has long fascinated us because of its many similarities to the earth and because of the possibility that life might exist there. The flyby of the crewless spacecraft Mariner 4 past the planet in 1965 started an era of intense exploration that still continues. Following several crewless flybys and orbiters launched by the United States (Mariners 4, 6, 7, and 9) and by the Soviet Union (Mars 3, 4, 5, and 6), the first successful soft landing of a spacecraft on another planet was achieved on July 20, 1976, when the U.S. spacecraft Viking 1 landed on the surface of Mars. Since then, Mars has been visited by several unpiloted craft, including the Mars Pathfinder spacecraft in 1997 and the Mars Global Surveyor from 1997 to 2006. (Squyres, 12) When images from these two probes were compared, scientists began to suspect that water had once flowed at several locations. Since 2004, NASA’s (National Aeronautics and Space Administration’s) Mars Exploration Rovers twin robot-geologists Spirit and Opportunity have explored the harsh Martian environment in search of water. The Phoenix Mars Lander, which safely reached the planet’s the North Pole in 2008, will analyze the icy soil for evidence of past microbial life. Mars is now perceived as a planet of spectacularly diverse topography with huge volcanoes, deep canyons, dry riverbeds, and extensive sand seas. While evidence of life there continues to be elusive, Mars remains interesting for geologic, chemical, and meteorological comparisons with the earth (Paolo, p.89). Telescopic Observations Following the first telescopic observations of Mars by Galileo in 1610, the planet has been observed continually, with changes in its appearance noted and mapped. Mars is too distant for any surface relief to be discerned through the telescope. All that is seen are bright and dark markings, which may be in the atmosphere or on the surface. Most surface markings are in the equatorial regions, where various dark features contrast with the light areas or “deserts.” The shape and size of most markings change both seasonally and, slowly, over many years. Despite the many changes, the most prominent features are recognizable even on the earliest maps. The markings show poor correlation with topographic features revealed by spacecraft observations. Most are thought to result from thin deposits of windblown debris whose distribution changes with time. Bright polar caps are clearly visible through the telescope, and the larger size of the northern polar cap long has been recognized. Most of the changes in appearance through the telescope are due to atmospheric effects of various kinds. Large arrays of white clouds commonly form in the middle latitudes and may persist for weeks. Those around the volcanic centers of Tharsis and Elysium most likely form when the air cools as it rises over the high volcanic regions. Other white clouds probably are caused by the daily recycling of water between the soil and the lo