Mars has two moons, and on the night of August 1, 2013, NASA's Curiosity rover captured 41 images of them, as the larger moon, Phobos, passed in front of the smaller one, Deimos. In the video above, NASA has stitched together those images compressing the transit down from 55 seconds into about 10. NASA says that it is the first time a mission has documented one moon eclipsing the other from the planet's surface.
The two moons were discovered in 1877 by American astronomer Asaph Hall. Phobos, the inner and larger one, circles Mars at a remarkable speed, completing its orbit in fewer than eight hours. Though Phobos is much, much smaller than our own moon (its diameter is about 1 percent that of ours), it appears about half as wide in the night sky to a hypothetical martian (or, in this case, a very real robot) because its orbit is so much tighter. Astronomers believe that sometime in the next 100 million years, Phobos will break up and crash into the red planet. Meanwhile, Deimos, the smaller moon, is thought to be gradually moving farther away from the planet, much like our own moon is moving away from us.