Thanks for the link.
For me, a circular rainbow was a once-in-a-lifetime event. I was flying South in the evening near Sturgate, Lincs, England. There were dark clouds and rain to the East but a clear sunset to the West. A circular rainbow appeared around my left wing. Of course, no camera in the cockpit, duh.
Another time with another setting sun, I was in a Airbus window seat over the wing when I saw a dark line oscillating fore and aft randomly with about a yard amplitude. Much of the airflow over an Airbus wing is laminar (smooth layers), but inevitably changes to turbulent flow maybe 1/3 back from the leading edge. Somehow the setting sun was showing me the point of transition from laminar to turbulent - all the way out almost to the wing tip. I guess the oscillation was due to changes of angle of attack induced by the autopilot. That time my camera film was stuck inside, so no pic, duh..