On 6/15/2012 5:52, Le_Forgeron wrote:
> IIRC, the blue of the sky is due to the variant IOR (vs void) of the
> atmosphere for the "white" light: the blue is turned more toward the
> earth (well, sooner: it might explains a bit the redish-moon eclipse).

The sky is blue because the dust and other particles in the sky reflect blue 
light better than red light, because blue light is smaller than those 
particles and red light is larger.

So, when the sun is high (with little atmosphere between it and you), the 
sky is close to white near the sun, because the light doesn't get scattered 
much. The light that *does* get scattered winds up going behind you, 
bouncing off some dust, and returning to you to make the part of the sky 
behind you look lit up, preferentially blue.

When the sun is close to the horizon, the light is going through a lot of 
atmosphere, to the point where there's enough to reflect the blue light back 
towards the people who are still experiencing noon, and all you see is the 
red light that didn't get scattered. Hence, ruddy sunsets.

-- 
Darren New, San Diego CA, USA (PST)
   "Oh no! We're out of code juice!"
   "Don't panic. There's beans and filters
    in the cabinet."

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