Bruce Murray Space Image Library
Saturn's north polar hexagon (animation)
Some of the heat radiation is blocked by clouds floating in Saturn's atmosphere at about 75 kilometers below the cloud tops that can be seen in visible wavelengths. The pressure at that level is about three times Earth's atmospheric pressure. The patterns in the image are created by alternating cloudy and clear areas. The images have been contrast-reversed so that the clouds show up as bright spots, while open areas appear dark. The 37 frames in the animation (only 13 of which are shown in the thumbnail version) were taken over a period of about an hour, as Saturn rotated about 30 degrees.
Learn more at Photojournal. There is a higher-resolution still version.