Original URL: http://www.theregister.co.uk/2005/02/09/blue_saturn/
Saturn sings the blues
A sunny day at the North Pole
The latest pictures from the Cassini mission show that Saturn's northern hemisphere is currently a vivid blue, with only a few white clouds in the upper atmosphere.
A relatively cloud-free sky on Saturn means that light travels along a longer path than it does in the cloudier southern sky. The shorter, blue, wavelengths are scattered by the gases in the atmosphere, lending the planet its sapphire hue.
The image shows dark bands running around the planet's atmosphere. These are not the cloud bands they seem to be, but shadows cast by Saturn's rings. Because of the angle of the rings to the sun, the shadows in the higher latitudes are cast by the outer rings. The uppermost shadow in the picture is cast by the upper edge of the A ring.
Scientists suspect that these shadows cool the Northern hemisphere, and that this is why it is relatively cloud-free around the Northern pole. ®