Contrail, Shadow and Halo
July 16, 2004
The fascinating photo above was taken above Quimper, Bretagne, France on June 25, 2004 and shows a jet contrail and its shadow exiting a 22 degree solar halo. At first glance, it appears that the contrail is underneath the cirrus veil, but its shadow demonstrates that in fact, the jet is above the cirrus displaying the halo. Halos can occur if hexagonal plate or column crystals in cirrus-type clouds are more or less randomly oriented. Sunlight enters one side of a crystal, is refracted, and then exits the opposite side, where it's again refracted by the same amount and in the same direction as the original refraction.
Photo details: DC Camedia 5060, 1/1500 s, 80 ISO, 110 mm focal lens, 1:5.6