Stars are Missing in the Sky
Why is the sky blue? This seemingly simple question has become so common on physics tests that it doesn’t frighten students anymore. While it’s easy for a layman to understand, it is not easy to answer. In fact, a detailed answer is not simple, but requires knowledge of atomic and molecular physics. The blue color of the sky is caused by the scattering of light off air particles, or the splitting of a directed light beam in other directions. This fact has been known for a long time, but interestingly, the scattering depends on the color of the light. Blue light is more strongly scattered than green or red, and so blue light is distributed over the entire daytime sky, while all other colors are mostly allowed to transmit directly through the atmosphere. The scattering of the blue light is so strong that considerable amounts of intense sunlight are spread across the sky, rather than reaching the ground. The light of the stars is outshined by the scattered sunlight and the stars are therefore obscured during the day.