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Basics
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A halo occurs around the sun when light is refracted as it passes through ice crystals. When a thin uniform cirrostratus cloud deck containing ice crystals covers the sky, the halo may be in the form of a complete circle as seen below in the middle.
There are many types of halos. One of special note is the parhelion or "sun dog." Sun dogs are luminous spots on both sides of the sun that occasionally occur with a halo (left).
A fog bow is caused by a process similar to that causing rainbows, but because of the very small size of the water droplets, the fog bow has no colors (right).
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| Example of Sun Dog (larger image) |
Example of Halo (larger image) |
Example of Fog Bow (larger image) |
