A glory is an optical phenomenon appearing much like an iconic Saint’s halo about the head of the observer which is produced by light backscattered (a combination of diffraction, reflection and refraction) towards its source by a cloud of uniformly-sized water droplets. The association with a halo is not coincidental, but derivative, though a real glory has multiple colored rings. Most people see only one ring. The glory, however, can show many rings when the cloud is made of uniform water droplets. Sometimes the rings fluctuate wildly in size. This happens when a plane, for instance, skirts a canyon of clouds and its glory shadow comes and goes.
The angular size is much smaller than a rainbow, about 5° to 20°, depending on the size of the droplets. Since it is seen in the direction opposite the sun, it is most commonly observed while airborne, with the glory surrounding the airplane’s shadow on clouds (this is often called The Glory of the Pilot).