Here's a fantastic detailed explanation of the geometry and what's going on with each visual element of the picture, from Slate:
http://mobile.slate.com/blogs/bad_astronomy/2012/12/20/satur...
http://mobile.slate.com/blogs/bad_astronomy/2012/12/20/satur...
Quote: "Interior to the G ring and above the brighter main rings is the pale blue dot of Earth. Cassini views its point of origin from over a billion kilometers (and close to a billion miles) away in the icy depths of the outer solar system."
(Saturn is "icy depths of the outer solar system"? Well, I'll never! That's the Oort cloud. This is merely the better neighborhood, with the fancy planets ...)
If you're still having trouble wrapping your mind around the shadowy part... Look at this image and imagine the light source coming from behind instead:
http://upload.wikimedia.org/wikipedia/commons/0/0e/Saturn_HS...