Lunar Halos

      Alaska North Slope

A scene captured by James Helmericks at 70° North in the Colville River Delta.

Ice crystals have glinted to create an almost complete paraselenic circle the lunar counterpart of the sun’s parhelic circle. It is studded with four paraselenae or moondogs. Two flank the moon and two much rarer ones are 120° away (one of those is faint).

A 22° halo circles the moon and it is topped by an upper tangent arc.

Just above that is a trace of a Parry arc. Farther from the moon near the horizon to the left of the building is an infralateral arc . Near to the zenith are hints of a supralateral arc and circumzenithal arc – just possible at this lunar altitude.

The straight line passing through the left hand moon dog is probably a light pillar generated by a lamp behind the building.

Images ©James Helmericks, shown with permission
Upper tangent arc and just above it a Parry arc
Paraselenic circle from plate crystals and horizontal columns

Moon dogs or paraselenae
The lunar equivalent of 22° parhelia or sundogs. Their name can be misleading because they are only 22° away when the sun or moon is on the horizon. They get more and more distant as the sun/moon climbs.

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A hint of a circumzenithal arc (plates) and supralateral arc (horizontal column crystals).
120° paraselenae

Rays enter the upper face of horizontal plate crystals, reflect internally from two side faces and leave through the lower hexagonal face. 120° paraselenae and parhelia have no colour