Clouds over La Silla

The Atacama Desert is the ideal location for ESO telescopes, including those seen in this image, at ESO's La Silla Observatory.

The skies here are free from the light pollution of towns and cities, and are usually stunningly clear. However, as this image shows, clouds do make an occasional appearance. Although perhaps providing some welcome shade for the desert's wildlife, they are far from ideal when astronomers are trying to observe astronomical objects beyond them.