Light never travels in a perfectly straight line. 

The path of light through air (or any other substance) depends on the density of the gas.  Add energy to the air in the form of heat or radiation and the refractive index will change.  What we perceive is never the true nature of an object, but rather what it looks like as photons bounce off of it and travel through the interactive medium of our atmosphere.  What you eventually see as a photograph depends on your frame of reference.

Lucas James is a fine art photographer based in Manchester, NH.  Anisotropic Images Fine Art Photography.