A glory is an interference effect which produces a circle around the anti solar point of the observer on cloud or fog. The diameter of the circle depends on a number of things including the distance to the cloud. When ever you are in an aircraft try and determine where the position of the sun is, and thus where the shadow of the aircraft will be. If the shadow lands on cloud look for a slightly rainbow coloured circle around the shadow. This is a glory.
A glory seen from a helicopter
A glory seen from an aircraft which has a contrail. The shadow of the contrail is seen as a dark line from the center of the glory, where the shadow of the aircraft is.
A glory seen under the wing of an aircraft.