What you're seeing here (below) is an awesome image of Saturn's moon Dione as it passes right infron of the moon Titan taken by Cassini spacecraft. The detail in the image below is stunning, and you can also see the mist of Titan's atmosphere blushing around the curve of the lake-covered moon.
Image credit: NASA / JPL / SSI / Gordan Ugarkovic
This image was taken by Cassini spacecraft and it was calibrated by Gordon Ugarkovic, who provides this info about the shot:
Cassini NAC RGB sight taken 2011-12-07 20:53 UTC.
Distance to Titan: 3.163 million km
Distance to Dione: 1.611 million km
Phase angle: 61 deg
You can also see more of Ugarkovic's stunning work in his Flickr stream.