ANST - Why?

[Angela Bellavance]

On Tue, 1 Sep 1998, Dennis Grace wrote:

> >Why is the sky blue?
> 
> The sky is blue because the gasses in 
> Earth's atmosphere don't block the higher energy wavelengths of light as 
> easily as well as they block the red-thru-green light.  Since the blue 
> component of that light is more prominent than the violet component, we 
> see only blue.

A valiant effort! but not quite correct.  The sky appears blue because the
higher wavelengths of light are more readily _scattered_ by the
atmosphere. Our eyes work by picking up scattered light.  If the blue were
being absorbed, we wouldn't be able to see it at all.  During
sunsets/sunrises everything takes on a yellow-reddish hue because the
sunlight, having traveled through a great deal more atmosphere then at
noon, has had all the blue scattered out of it leaving the yellow and
lower wavelenths behind to be scattered by dust particles.  Since dust
scatters lower wavelengths more readily, this is also why the sky appears
"bluer" or "deeper" after a rainstorm (the rain having washed the
particulate matter out of the air and hence having removed the
green-yellow-red scatter that whitens out the blue).

Respectfully, Angela

-a third year physics grad student who really should be doing class
reading right now! :) - 
_______
Angela Bellavance 
bellavan at rice.edu			home: (630) 293-7086
http://www.owlnet.rice.edu/~bellavan/	work: (630) 840-4144(NM) or -5708(KH) 
"It has yet to be proven that intelligence has any survival value."
				- Arthur C. Clarke

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