The Cassini spacecraft just keeps sending back splendiferous images of the Saturn system. It's latest gym is below (get big versions here!)
Cassini is on the night side of Saturn. You can see the sunlight scattering through the upper part of Saturn's atmosphere producing that neat effect. The Moon is Enceladus. Look closely and you see a little blurry streak coming out of the bottom of Enceladus. That is a geyser erupting!
Okay, it gets more interesting. Since we see the night side of Saturn, we should be seeing the night side of Enceladus, so why is it so bright and easy to see? Two things are going on here. First, the imaging team brightened Enceladus by a factor of two relative to Saturn. Second, the Moon is being lit by sunlight reflected from the other side of Saturn...aka Saturnshine. You ever see a slender crescent Moon and the dark side is illuminated just a little bit so you can make out the outline? The dark side of the Moon is being lit by sunlight reflected from the Earth and given the name Earthshine. Same thing here with Enceladus.Love those Cassini images.
Reprinted with permission from the Half-Astrophysicist Blog.