Cloud Shadows
Imaged by Ed Pina.

Cloud shadows, or their inverse, crepuscular rays, are one of the few atmospheric optics effects that are "real".

They are real in the sense that they are three-dimensional objects, they occupy space, an aircraft can fly through them. Halos, rainbows, glories and most other effects are bundles of rays that meet your eye - they do not exist in space and cannot be touched or looked at from another angle.

Cloud shadows are long columns of dark air stretching away from the sun from clouds. Sometimes, as here, the shadow tube intercepts a lower cloud layer and blocks that too from the sun.

Image ©Ed Pina, shown with permission.