Atmospheric Optical Phenomena

Light that bounces off very small objects is not reflected uniformly, but is scattered in all directions. The process of scattering is responsible for the fact that humans observe the sky as blue. When white light from the sun collides with molecules of oxygen and nitrogen, it is scattered selectively. That is, light with shorter wavelengths—blue, green, indigo, and violet—is scattered more strongly than is light with longer wavelengths—red, orange, and yellow. No matter where a person stands on Earth's surface, she or he is more likely to see the bluish light scattered by air molecules than the light of other hues.