Contrail Shadows at Sunrise

This was a particularly interesting sunrise. One of the times I was really happy I was carrying my camera with me everywhere.

This photo made me think quite a bit about the position of the clouds in the atmosphere. If you take a look at the contrails, they appear to be casting shadows up on the clouds. This is a result of an optical illusion.

The contrails are at a higher level than the clouds. They appear closer because they are much denser than the high altitude Cirrus clouds. The clouds are made of ice crystals, blown in the wind like grains of sand. And, being thin and wispy, you see more blue sky through them which contributes to the illusion.

All other things equal, your brain is wired to see a bluer object as being further away. Like a mountain in the distance, when there is more atmosphere between you and the object you are viewing, the object appears bluer.

There are actually two layers of clouds, one right below the trails and another, much thinner and hazier one, quite a bit lower. This accounts for the double shadow.