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Circumhorizon Arc
Imaged by Sue Wild-Kim during the great Spokane, Washington display June '06. ©Sue Wild-Kim, shown with permission.

This ice halo is a herald of summer because the sun has to be at least 58° high. It is huge and lies beneath the sun parallel to the horizon. Sunlight passing into the side faces of plate crystals and leaving through the large lower face forms it.

Circumhorizon arc     ice crystals