Parhelion

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parhelion

(Also called sun dog.) A halo in the form of a colored spot at the same angular elevation as the sun.

The lunar counterpart is a paraselene. The most common parhelia are seen about 22° on either side of the sun. That angular distance increases from 22° when the sun is on the horizon to over twice that when the sun climbs to 60°. The sun side of a parhelion is reddish. The parhelia of 22° can be explained by refraction in hexagonal crystals falling with principal axes vertical. The effective prism angle is 60° when the sun is on the horizon, but this increases as the sun climbs, resulting in greater displacement of the parhelion.


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