Christophe Suarez (photography) caught this magnificent lunar circumhorizon arc during a freezing cold night in the Alps. Orion is visible above the arc ©Christophe Suarez, shown with permission.
Near horizontal hexagonal plate crystals produce the huge circumhorizon arc (CHA). Rays are refracted between facets inclined 90° to each other with a resulting large angular spread of colour.
In contrast, the lunar CHA is best in the northern midwinter when the near full moon is at its highest.