Why Is The Sky Blue?

So, anyone know why the sky's blue?

• I was just thinking one day, and I thought, why does everyone color water blue? Well, obviously pools, the ocean, lakes, etc, all seem blue. But we all know that water is CLEAR!!!! What the heck? Well, duh, water is reflective, and what's always above water, no matter what?..... SKY. Now, we all know that air is clear..... the water molecules in the air are clear, clouds, yes seem white / gray sometimes, but the clear beautiful sky is blue...... WHY? At first I thought of it as a chicken and the egg thing, the water's blue, the sky's blue, the sky's blue, the water's blue.... but that can't be right..... so.... WHY'S THE SKY BLUE? Thanks.

• Answer:

  Lots of people know and lots of people think they know and get it wrong.... It is basically down to scattering of light by atoms/molecules/dust in the earth's atmosphere Light scattering by particles depends on the relative "sizes" of the photons and the particles. In the case of visible light, molecules are much smaller than the wavelength of light, so blue light gets scattered much more than red light. So as light from the sun enters the atmosphere, more blue photons get reflected (not absorbed) by molecules than red photons - but then the blue photons get reflected again and again until they reach us. So the blue light comes from all over, the red light comes almost straight from the sun. This is also why the sun looks redder at sunrise and sunset - the light's path through the atmosphere is longer when the sun is on the horizon than when it is high in the sky. Interaction of light with the atmosphere does all sorts of weird and wonderful things that physics can explain: http://hyperphysics.phy-astr.gsu.edu/Hbase/atmos/atmoscon.html#c1 Or look at the many times this question has been asked before by searching for your question – I think it has been asked over 7000 times