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>
>
>
> William and Wayne are right: the frequency changes, not the speed of  
> light. The light from distant, redshifted galaxies has always been  
> moving at the same speed ever since it started out on its trip to us.
>

Assuming that it has traveled in a vacuum all that time, right?   
Passing through gas, our atmosphere, water changes the speed  
significantly...how do I know?  Google said so...
"
If light travels not through empty space but rather through a gas  
(air) or a transparent fluid or solid, then the speed of the light in  
that substance is less than the speed of light in empty space. The  
ratio of the speed of light in empty space and the speed of light in a  
substance is equal to the index of refraction of that substance. The  
index of refraction of water is about 1.4 (depending on the color of  
the light), so the speed of light in water is equal to about c/1.4  
which is about 0.7c, which is about 210,000,000 m/s or about 130,000  
miles per second."

<http://www.astro.uu.nl/~strous/AA/en/antwoorden/licht.html>

Eric Siegel
Director and Chief Content Officer
New York Hall of Science
47-01 111th Street
Queens, NY 11368
www.nyscience.org
718.699.0005 x 317
esiegel at nyscience dot org


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