Circumhorizontal Halo

August 19, 2002


Referred by: Michael Ellestad
Summary authors & editors: Jim Foster; Michael Ellestad

The photo above was taken this past May (May 15) in Adams County, Ohio and shows a portion of a 22 degree halo around the Sun (actually, circumscribed halos overlapping each other) plus a circumhorizontal arc - the bright colorful arc closest to the horizon. Circumhorizontal arcs can't be seen unless the Sun is at least 58 degrees above the horizon, therefore they're only observed when the Sun is high in the sky - summer months near solar noon. These gentle arcs only occur when sunlight enters the side face of a hexagonal plate crystal and exits through the bottom face.

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