Jet aircraft flying at high altitudes often produce a trail of condensed vapor called a contrail. The mixing of hot exhaust gases from the engines with cold outside air causes ice crystals to form on particles in the exhaust. A contrail evaporates rapidly when the relative humidity of the surrounding air is low. If the humidity is high, a contrail may stay visible as cirrus-like clouds for many hours. In this image, the contrail is accompanied by cloud iridescence, delicate colors that occur when sunlight is diffracted as it passes through clouds that are thin and have similar size droplets.
