Parhelic Circle and Paranthelion

January 24, 2006

Parheliccircle copy

Provided and copyright by: Daniel Herron, Atlanta Astronomy Club
Summary authors & editors: Daniel Herron; Jim Foster

The photo above shows a wonderful example of a parhelic circle and paranthelion, captured over Alpharetta, Georgia on December 16, 2005. A parhelic circle is a narrow horizontal band which under ideal circumstances encircles the sky at the solar altitude -- it's devoid of color. This rather rare type of halo is formed when sunlight reflects from the front surface of any ice crystal face (in cirrus clouds) lying in the vertical plane -- these crystals must be similarly oriented. The paranthelion is a spot of white light found at the solar elevation an at an azimuth of approximately 120 degrees relative to the Sun. Though a number of crystal shapes and orientations can cause the paranthelion, it's nonetheless rarely seen. The fact that the parhelic circle band and paranthelion are colorless is a clue that this phenomenon results from reflection processes.

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