Circumzenithal and circumhorizontal arcs.

The circumzenithal and circumhorizontal arcs are perhaps the most beautiful of the halo phenomena. They are very colorful and only the rainbow comes close to match their splendor.

The CZA takes the form of a quarter of a circle centered on the zenith and facing the sun. The CZA only forms when the sun is 32° or less above the horizon. It is brightest at a sun altitude of 22°.

The CHA is a colored band of light parallel to the horizon on the same side of the sky as the sun. The CHA appears only when the sun is higher than 57.8° and therefore the CHA and the CZA can never be seen at the same time.


 
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