Sunset from Earth orbit,seen from the Space Shuttle Discovery. The glow of the setting Sun is lighting up the layers of the atmosphere on the gently curving horizon that separates the Earth (top) from space (bottom). The first layer,the troposphere (orange),can be between 7-25 kilometres thick,and contains most of the atmosphere. Above the troposphere,the next layer,the stratosphere (pale blue),reaches up to heights of about 50 kilometres. Sunsets are orange because the sunlight travels through more of the atmosphere and other colours (such as blue),which are scattered more than red colours,do not reach the eye. Photographed on 15 July 2006 during mission STS-121 |