Here is a picture of a "pilot halo" taken a split-second before we descended into some clouds. The sun is directly behind us, so it focuses our shadow on the clouds in front of us. Then, for some reason beyond this particular pilot's ability to understand, the light refracts around the plane and places a circular rainbow around the shadow! ...thus the name "pilot halo." If the sun is on one side or the other and we are flying close enough to a deck of clouds, it will do the same, but from a profile angle... and you in the back would be able to see it as well!