From the "Viking Archive" - Viking 1: Solar Eclypse on Mars

Possibly the most unusual of all Viking Lander pictures records the passage of Phobos' shadow during a solar eclipse. On Earth the apparent size of the Moon is exactly the same as that of the much larger but more distant Sun. Consequently, direct sunlight is completely blocked out during a total solar eclipse. On Mars, Phobos covers only 1/4 of the solar disc. However, passage of the penumbral shadow causes a general drop in light level that is instrumentally detectable. This frame is a repeated line scan image looking back across Viking Lander 1. The colors have been distorted purposely to enhance detail. The blue and white horizontal stripes correspond to test chart patches. The brownish stripes in the middle represent the martian surface visible above the spacecraft. Note a decrease in light levels in the sky midway through the imaging event. The darkening, caused by the passage of the penumbral shadow of Phobos, is present over approx. 100 vertical lines. Moving at about 2 Km/sec, the shadow took about 20 sec to pass over the Lander.