As can be seen in Figure 1, the sky of Mars has considerable dust content, which scatters the incident sunlight. This dust content varies considerably, depending on the dust storms. When the dust levels are high (typically near perihelion; around the northern hemisphere winter [4]) the optical depth of the atmosphere can be much greater than one [1]. At these times very little direct sunlight reaches the Martian surface, and nearly all of the light reaching the surface is diffuse scattering from the atmospheric dust. Despite the low amounts of direct insolation, however, the total light reaching the surface is appreciable. Figure 2 (from reference 1) shows the total sunlight availability (integrated over a day) for a horizontally oriented surface, showing the variation during the year. Like Earth, Mars has seasons due to its axial tilt. For locations off the equator, the number of hours of sunlight varies during the year. This has a considerable effect on the design of solar systems, particularly if they are to be designed for
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