Lunar Halo
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.

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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.

The solar CHA is a summertime halo as the sun must be higher than ~58°.

In contrast, the lunar CHA is best in the northern midwinter when the near full moon is at its highest.