May 10, 2003
The photograph above shows a portion of the virgin grasslands of the Inner Mongolia Autonomous Region in northern China. Beautiful blue skies, green grass and simple people living a simple life. This is a land of little topography and big skies. In this case, the cumulus-fractus clouds give definition to the azure blue sky. Notice that when the view of the horizon is unobstructed, the blue color appears more and more washed out as the horizon is approached. This is due to multiple scattering of sunlight. In essence, the path-length of light is longer when looking toward the horizon than when viewing the sky overhead, and as a result, there are more air molecules to scatter the sunlight.