This crescent phase picture of Mars was taken by Viking 2 on August 5 from a distance of about 400,000 kilometers (250,000 miles) as it was approaching the planet for its orbit insertion maneuver. Viking 2 went into orbit around the planet at 5:30 A.M., PDT today. The view is of the morning side. Toward the top of the picture, the four dark spots are the huge volcanoes of the Tharsis region. They appear dark partly because clouds and haze cover this region at this time of day, and the volcanoes stand higher than the clouds. In the bottom part of the picture, at the tip of the crescent, is a bright circular feature, the large impact basin, Argyre. This basin shows up brightly because its floor is covered with frost.
NASA
<a rel="nofollow" class="external free" href="http://apod.nasa.gov/apod/image/0103/barsoom.jpg">http://apod.nasa.gov/apod/image/0103/barsoom.jpg</a> (P-17442)