MadSci Network: Physics

Re: Is the blue of the sky made of blue and green?

Date: Wed Dec 16 08:43:45 1998
Posted By: John Link, MadSci Admin
Area of science: Physics
ID: 913751270.Ph

The question is:
"I know the sky's blue because only some wavelengths are 
scattered. But isn't green light scattered, too? (Most violet, I 
think, gets absorbed) And don't the green and blue of the 
rainbow add up to the cyan we see in the sky?"

The answer:
You are correct in your first question.  We call the sky blue
because that is the color that our eyes and brain interpret the
broad spectrum of scattered light to be.  The broad spectrum
of scattered light has a broad peak in the region of wavelengths
that we call blue.

I'm not actually sure what you mean by your second question about
the rainbow.  The blue of the sky is certainly a result of 
scattered "white" light from the sun, and the colors of the rainbow
also come from sunlight, but we obviously don't need a rainbow
around in order to see blue sky!!  If you mean that the cyan in
the rainbow itself is a combination of blue and green then that
is not quite correct, because the cyan color is itself a certain
narrow range of wavelengths and would be there even if the blue
and green were not.

I hope this helps!!

John Link
MadSci Physicist

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