Re: pinhole curious rainbow

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From: Paul Doherty (pauld@exploratorium.edu)
Date: Sat Feb 24 2001 - 15:40:09 PST 

Message-Id: <l0311070db6bdf5fc2975@[192.174.2.173]>
Date: Sat, 24 Feb 2001 15:40:09 -0800
From: Paul Doherty <pauld@exploratorium.edu>
Subject: Re: pinhole curious rainbow

Hi Eric

You have just given a perfect description of a circumzenithal arc.
It is made when sunlight refracts through prisms of ice in the air.
The ice prisms are flat and fall with their flat faces parallel to the
earth. The sunlight enters a face toward the sun and exits through the base
thus going through a 90 degree prism.
Dispersion separates out the colors.
It is one of the most colorful apparitions in the sky.

Paul Doherty

>hello
>
>Yesterday at about 4:00 PM I saw a curious little
>rainbow hovering near the sun. I've seen rainbow-like
>halos around the sun before, but this was different.
>It was a short arc bending AWAY from the sun. If I
>remember correctly, the red was closest to the sun and
>violet away from the sun. The rainbow was almost
>directly overhead with the sun fairly low in the sky.
>
>And while we're at it, I've forgotten exactly what a
>sun dog is. Was what I saw a sun dog?
>
>--eric
>
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Paul "But it is more complicated than that!" Doherty,
Senior Staff Scientist, The Exploratorium.
pauld@exploratorium.edu, www.exo.net/~pauld

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