The image was taken through a spectral filter centered on wavelengths of light that are strongly absorbed by methane gas. Hence, any light making it through this filter to the camera's detector has bounced off clouds that are high in the atmosphere, making them visible, while light passing through the cloud-free surroundings gets absorbed by the methane gas there before it reaches the lower clouds. The image was taken with the Cassini spacecraft wide-angle camera on January 5th, 2009, using a spectral filter sensitive to wavelengths of near-infrared light centered at 890 nanometers. The view was acquired at a distance of approximately 711,000 kilometers (442,000 miles) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 106 degrees. Image scale is 39 kilometers (24 miles) per pixel.
(Sources: NASA/JPL /Space Science Institute)