An atmospheric optical feature produced by interactions with ice crystals. A common halo comes from a prism path in hexagonal crystals; minimum deviation concentrates rays near its inner angular boundary. This differs from the liquid-water path of a rainbow.[ref]
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A halo is an optical phenomenon that appears around the sun or moon, typically as a bright ring or circle. Halos are caused by the refraction, reflection, and dispersion of light, usually sunlight or moonlight, through ice crystals suspended in the atmosphere, often in cirrus or cirrostratus clouds. The most common type of halo is the 22-degree halo, which forms a circle with a radius of approximately 22 degrees around the sun or moon.