A Hubble Telescope image shows the progress of four moons transiting Saturn. NASA has released these images showing four moons crossing the face of Saturn at the same time. Such an event is pretty rare, and very cool. The moons are (from left to right) Enceladus, Dione, Titan, and Mimas. You can also see the shadows of Enceladus and Dione on the planet's cloudtops, too. [CFP]