Today's Image of Mars shows what different stages of a solar eclipse by Phobos looks like on Mars. Phobos is the larger of two Martian Moons. These three images were taken by Mars Exploration Rover Opportunity on the 45th sol (Martian day) of its mission.
Phobos is only 27km in diameter at its longest point, so as you can see it doesn't completely block out the Sun.
Clicking on the image will take you to the original NASA press release on these images from March 11 2004.