Earth and Moon seen from Mars by Mars Global Surveyor spacecraft

This is the first image of Earth ever taken from another planet that actually shows our home as a planetary disk. Because Earth and the Moon are closer to the Sun than Mars, they exhibit phases, just as the Moon, Venus, and Mercury do when viewed from Earth. As seen from Mars by the NASA Mars Global Surveyor on May 8, 2003, at 13:00 GMT (6:00 a.m. PDT), Earth and the Moon appeared in the evening sky. This Earth/Moon image has been specially processed to allow both Earth (with an apparent magnitude of -2.5) and the much darker Moon (with an apparent magnitude of +0.9) to be visible together. The bright area at the top of the image of Earth is cloud cover over central and eastern North America. Below that, a darker area includes Central America and the Gulf of Mexico. The bright feature near the center right of the crescent Earth consists of clouds over northern South America. The image also shows the Earth-facing hemisphere of the Moon, since the Moon was on the far side of Earth as viewed from Mars. The slightly lighter tone of the lower portion of the image of the Moon results from the large and conspicuous ray system associated with the crater Tycho.

Image Credit: NASA/JPL/Malin Space Science Systems
Explanation from: http://earthobservatory.nasa.gov/IOTD/view.php?id=3481