Both Ends of the Rainbow

A double rainbow was captured when heading through the glaciated Benasque valley, located in the heart of the Pyrenees. The photo was taken just before the sunset, after heavy rainfall.
A rainbow is caused by reflection and dispersion of light in water droplets. Second rainbow arc results from one reflection more than in the first one, thus the rainbow colours are "reverted". The geometry causes the region between arcs to be darker and the area below the primary arc lighter. The inter-arc area is sometimes called "Alexander's dark band", named after Alexander of Aphrodisias.