Passing through the luminary and parallel to the horizon, there is a white luminous circle, the parhelic circle (P), on which a number of images of the luminary appear.
The most brilliant are situated at the intersections of the inner halo and the parhelic circle; these are known as parhelia (denoted by the letter p in the figures) (from the Gr.
The other images on the parhelic circle are the paranthelia (q) and the anthelion (a) (from the Greek av-ri, opposite, and iXcos, the sun).
Thomas Young explained the parhelic circle (P) as due to reflection from the vertical faces of the long prisms and the bases of the short ones.
When the sun is near the horizon the rays fall upon the principal section of the prisms; the minimum deviation for such rays is 22 °, and consequently the parhelia are not only on the inner halo, but also on the parhelic circle.
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