NASA / JPL-Caltech / SSI / animation by Glen Nagle
Saturn's rotating aurora (excerpt)
This animation consists of 21 frames captured by Cassini on 7 October 2009, focused near Saturn's north pole on the night side of the planet. Each frame is a long exposure, causing background stars to extend into long streaks. There are other small pointlike image artifacts that do not move from frame to frame (so they are most likely hot pixels or some other sort of thing internal to the instrument). There are also occasional cosmic ray hits that produce one-time streaks that aren't visible in subsequent frames. As Saturn rotates, the aurora flares. This is just an excerpt of a much longer animation.