A thin colored line

A thin colored line

Fig. 3.2 . The brilliant red of the setting Sun illuminates the thin atmosphere that warms and protects us. Without this atmospheric membrane we could not breathe and water would freeze. It is dust in the dense lower atmosphere that scatters red sunlight; molecules that are higher up in the air scatter blue sunlight, coloring the sky blue. This image was photographed on 3 June 2007 by an Expedition 15 crewmember on the International Space Station. (Courtesy of NASA.)

Copyright 2010, Professor Kenneth R. Lang, Tufts University