Sennadar Forums

Firestaff Series, "The Questing Game", chapter 19, at about 3/4 of the page:

"I asked the same thing.  He said that the sunlight hits the air at an angle that makes the air absorb or reflect away most of the other colors, making the sky appear to be blue.  And when it's sunrise or sunset, the sun strikes the air at a different angle, which makes it look a different color."

That is not exactly true. The reason of why the sky is blue (at least on Earth, with ordinary physics and standard air composition) is that the light gets scattered on gas molecules (not large ones like dust in the desert, or water vapour in the clouds) - actually it gets absorbed and emitted again (this time in random direction). It is called Rayleigh scattering. The higher frequencies gets scattered more, so there is more blue light (high end of visible spectrum) that gets scattered than any other color. So the ambient color of the sky is due to the scattering of blue light. It has next to nothing to do with the angle - that is beside the fact that if you look at the sun you will see mainly the light going in straigh line, not scattered. If not for atmosphere the sky would be black.

The setting and the rising sun is red because this time the light from the sun must travel (in straight line) through thick layer of atmosphere. The blue light gets scattered away, next green... so only red light (low end of visible spectrum) remains.

In a few words: the sky is blue because the light from Sun which otherwise would go to us gets scattered towards us, and blue is most strongly scattered. The setting/rising sun is red, because the blue (and green) color is taken from it.

URL: http://www.sciencemadesimple.com/sky_blue.html

funny that you mention it...
i study physics, and i once have worked in the cargo dept. of vienna airport for money.
one day one of the workers there asked me why i study physics/what i can do with it, and i told him that i can tell him why the sky is blue, and he was like 'What? That can be explained??'
and btw full acknowledgement to the explanation...

shadowhawk wrote:The setting and the rising sun is red because this time the light from the sun must travel (in straight line) through thick layer of atmosphere. The blue light gets scattered away, next green... so only red light (low end of visible spectrum) remains.

*puts flameproof suit on*
So, why don't we have the sky going from Blue, to Green, to Orange/Red during sunsets?

spec8472 wrote:*puts flameproof suit on*
So, why don't we have the sky going from Blue, to Green, to Orange/Red during sunsets?

Check the URL I've given. There they are pictures.

Sky is blue because blue scatters strongest. The ambient light is the light which would not go to uour eyes without scattering.

The light directly from the sun is white. It seems yellow when travelling thru thin layer of atmosphere (at noon), it seems red when travelling thru thick layer of atmosphere, which takes out blue (and green), leaving red.

The water is blue for mainly the same reason. And deep water is blue-green.

I may be wrong, but I am fairly sure that the Rayleigh scattering is not actually caused by the absorption and re-emittion of light by the molecules of the air.  This would cause the sky to me more white than anything, although maintain red sunsets because it would not necessarily re-emit the same wavelength.  The scattering is more due to small differences in pressure within very small volumes (If you take the air and split it up into small sections the size of which has an average of 20 molecules in it, it is conceivable that the sections would vary greatly in how many molecules they have).  It is this variation that causes a difference in the index of refraction of the air, thereby "scattering" the light due to the reflections at the indeces.  The lower the wavelength the more the light is affected by these indices and scattered, thus causing the sky to appear blue.  

ohtochooseaname wrote:I may be wrong, but I am fairly sure that the Rayleigh scattering is not actually caused by the absorption and re-emittion of light by the molecules of the air. [...] The scattering is more due to small differences in pressure within very small volumes.

You are (most probably) right, that the Rayleight scattering is on density fluctuations, not on molecules itself.

you may want to check http://www.wordiq.com/definition/Rayleigh_scattering and
http://www.wordiq.com/definition/Rayleigh_scattering on this..

one small flaw in your argument ohto: the wavelength of the scattered light remains the same...

taltos