Sunset, seen from the International Space Station (ISS). The glow of the setting Sun shows layers of the atmosphere. The first layer, the troposphere (orange), can be between 7-25 kilometres thick. It contains most of the atmosphere. Here, clouds have formed at the top of the troposphere. The Earth (bottom) is dark. 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. The ISS orbits Earth at an altitude of some 380 kilometres. Photographed on 28 July 2003.