PITTSBURGH (KDKA) — When you hear the word halo, you may think of an angel. The topic here is halos, but these ones are in the sky, and something I get asked about a lot.
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They are sun halos, or the rainbow ring around the sun, and moon halos. Those are the ring around the moon.
They are caused by cirrus clouds. Those are the high, thin clouds way up in the sky. Since they occur so high up, greater than 20-thousand feet where temperatures are below freezing, those clouds are comprised of millions and millions of tiny ice crystals.
Light is refracted as it enters through one face of the hexagon shaped ice crystals and is then refracted again when the light exits the other side. This light is sent outward, creating the halo. When that light is refracted inside an ice crystal, or even liquid water, the light is broken up into all of the colors that make up the light, just like a rainbow. You can even sometimes see that rainbow effect when halos happen around the sun.
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While the moon does not create light, it does reflect sunlight back to Earth. That light is then refracted in the ice crystals to create the halo. While it isn’t direct sunlight, the moon reflects enough light for a halo to be created.
These are also called 22° halos. That may seem like a weird name, but there is a reason for it. When light enters those hexagonal shaped ice crystals, that light is deflected between 22⁰ and 50⁰ .
This occurs more at angles of about 22°, so most of the light is deflected at this angle creating the halo.
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