A Double Rainbow

by Tammy
(Barrie, Ont.)

A double rainbow

October 18th at 6:15 pm in Barrie
a beautiful double rainbow appeared and gone within 15 minutes.

Barry's Response - Thank you for this, Tammy. We have a number of interesting variations on the rainbow. I found them listed on wikipedia.

The double rainbow you have photographed shows two distinct bows, where an observer could pick out the full spectrum in each one. They will note, also, that the colours appear in the opposite order in the second rainbow. Why? Because two reflection inside the drop cause the pattern to flip. In rare occasions, a bit of a third arc will be visible. Finally, take notice that the sky between the rainbows is darker than the rest of the sky.

What causes a rainbow? Refraction. Light comes to us directly from the sun, and it's composed of all the colours we know mixed together to give its characteristic yellow hue. A piece of transparent liquid or solid material lets light through it, but at a slower speed than the air. Not only does it slow down (a bit) but it bends when entering the object, such as a prism or water droplet.

It gets better. All those different colours, wavelengths actually, bend at different amounts, different angles, and come apart into the rainbow pattern, as shown on the old Pink Floyd album.

With spherical water droplets, like those suspended in the air after a rainstorm, the light enters, then REFLECTS of the inner backside of of the sphere and comes back. Not straight back, but bent by 42 degrees for red, at one end of the spectrum, and 40 degrees for violet at the other end.
Meteorology and optics. They make great partners.

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