The ESA's Rosetta, the first ever spacecraft whose destination is a comet, took this picture of the Earth at night. Large cities are clearly visible as mankind's presence on this planet is clearly visible-- even when the Sun is not.
Rosetta has a super complex trajectory is making its course to comet 67P Rosetta. This includes not one, but three gravity assist maneuvers around Earth and another around Mars. This truly will show how efficient current technology can accurately predict the course of our probes.
Once reaching comet 67P Rosetta, the craft will remain in orbit with the comet during its journey to and from the Sun. In a nutshell, Rosetta will ultimately tell us what comets are made of, why they are different (or the same) as other intersolar materials, and give us a better idea of what the surface of a comet actually looks like.
Interesting mission to be sure, and likely it will present us with new information while verifying what we already know about comets. The study of the origin of comets never looked so sweet... just check out this picture of a very overexposed Mars taken by Rosetta's wide-angle camera against the stunning backdrop of our Milky Way. Every astrophotographers dream--wide angle astrophotography with a twist: no atmosphere!