Moderators: richierich, ua900, PanAm_DC10, hOMSaR
747Whale wrote:The halo appearance is simply an effect of refraction; you could think of it as "bending" light. You can see some effects of refraction if you hold your hand against a bright light or bright sky; the fingers sometimes appear thinner than they are, and if you look at the the spaces between your fingers, you may see what look like lines paralleling your fingers; lines which aren't really there. This is refracted, or "bent" light, and can appear to concentrate around the shadow of an object if at the right focal length.
As others noted, it's quite common to see in the cloud and sometimes against the ground. It makes a pretty picture when flying directly into a cloud with the sun behind, sometimes seen in the cockpit and really hard to catch just at the right time to photograph.