MadSci Network: Astronomy
Query:

Re: Why was there an upside rainbow in the sky?

Date: Fri Jun 19 15:27:15 1998
Posted By: Mike Francis, Other (pls. specify below), Physics/Astronomy, Self employed/ Amazing Discoveries Productions
Area of science: Astronomy
ID: 897962923.As
Message:

MadSci Network: Astronomy
Query:

Dear Grace,

    You didn't say when you observed your "upside down" rainbow so I'm going to assume it was recently. There are actually two possible phenomena you might have seen. If it were winter I might suspect you'd seen a halo. Halos are created when ice crystals are floating in the upper atmosphere. As the Sun's light passes through these crystals it is refracted or bent to form a large ring around the Sun. This ring is usually 22 deg away from the Sun, though on rare occasions they may form at 46 deg or 90 deg, depending on the concentration of ice crystals and other atmospheric conditions.

    Since you're not living up near the arctic circle and it's not winter or early spring, my guess is you saw a corona, not to be confused with solar coronas. Coronas can be found when the lower atmosphere has suspended water droplets in the form of a very thin cloud. As the Sun's light passes through these droplets it is refracted to form a ring. Unlike rainbows, which you'll find in the direction opposite the Sun, coronas surround the Sun with rings that are usually less than 22 deg away from it. If there were clouds covering the Sun from your view you might have just been able to see the bottom of the corona.

    Consider yourself lucky. I've only seen a corona once. If you see one again, American Indians used to predict rain when they saw the Sun inside a corona, so get on your raincoat.


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