I dabble a bit with astronomy and like to discuss it. The latest series of pictures in the Big Picture blog are breathtaking.
The cool thing about this particular picture is not the big shadow running down on the rings. It's the shadow of the smaller particles that form the white ring towards the center.. if you notice closely, thay cast a shadow on the next set of rings.
Watch the entire series of images here.
On a related note, I'm reading Arthur C Clarke's Rama series..