Winter is approaching in the southern hemisphere of Saturn, and with this even colder season has come a blue hue that was present in the northern winter hemisphere several years ago when the Cassini spacecraft arrived to orbit the planet. The blue hue that marks winter on Saturn is likely caused reduction of ultraviolet sunlight and the haze it produces. That allows the atmosphere to be clearer, increasing Rayleigh scattering (scattering by molecules and smaller particles) and methane absorption. Both processes make the atmosphere appear blue. The small black dot seen to the right and up from image center, within the ring shadows of the A and F rings, is the shadow of the moon, Prometheus.
Image Credit: NASA