I’d tried searching, but sky [and] blue wasn’t a long enough search term.
I get that the sky is blue due to the fact that the visible radiation from the Sun is ‘scattered’ by the Earth’s atmosphere.
Using ROYGBIV as an acronym as to what humans perceive in the visible part of the EM spectrum, I can understand that we perceive Blue over Indigo and Violet due to photoreceptors in our eyes—our cones are more receptive to Blue. And maybe the Sun emits more light in the Blue wavelength than the higher—we see Blue because that’s what’s there and we don’t see the higher wavelengths even if they’re there because our eyes can see them.
My physics questions is: Why is blue light scattered to the point we see the sky blue instead of the lower wavelength colors?
The sky around the sun is blue at noon and red at sunset.
Why are the high-energy blue photons scattered by the atmosphere and low energy red photons cruising to the eye until sunset—where the air becomes too thick?
At least in regard to how photons hit the retina, which is how the brain interprets color. (that’s another story)
If I didn’t explain my question in my previous post:
Why does the atmoshpere deflect high energy blue light and not low enrgy red light?
As a layman, I would think that the high energy photons would speed through the atmosphere to the retina more than a low energy (red) photons source.
If I have it right, high energy blue wavelength photons do not hit my retina directly from the sun but reach it scattered by the atmosphere–the sky is blue. Whereas red photons make their way through the thicker atmosphere at sunset and hit my retina as filtered red light.
The Ozone layer is the culprit. It refreacts that color 90’, without it we’d be dead and have black skies.
I remember an interview I heard on NPR with I think John Glenn, he said that there are so many other colors to see without our natural filter of the atmosphere, he said they were indescribable because they simply don’t exsist down here.
Red at sunset is a similar thing just as white with high humidity, each particle is a different size and it depends on the angle of the light (red mornings too) and what particle is refracting/filtering the most.
These are dim memories of my physics classes from too long ago. If you don’t use it you really do lose it. Mine is rusting away.
The reason the sky is blue;
I didn’t know this till I came to the Straight Dope Board, but I think I do now, so let’s see what I can do;
The answer is light is scattered by Rayleigh scattering in the rarified upper atmosphere. Blue light is affected very much more than red light, or in fact ny of the other wavelengths;
Rayleigh scattering only occurs when tiny particles are suspended in an atmosphere a certain distance apart, like for instance fine water droplets or smoke;
if both of these are absent, the sky still seems blue because the very molecules of air are the right distance apart in the upper atmosphere to cause Rayleigh scattering of blue light.
According to this link, Rayleigh scattering doesn’t happen in the lower atmosphere because the molecules are too close together;
destructive interference cancels the scattering out.
*Scattering by the air
Air molecules in the low density upper atmosphere behave as Rayleigh scatterers. However, closer to the ground the air is too dense for Rayleigh scattering to be significant because waves from the closely adjacent scattering molecules overlap and destructively interfere. *
So when you look at the blue sky, and think that it seems to be a long way above your head- it is!
Rayleigh scattering explains most of it. The coefficient for scattering varies as 1/(wavelength) raised to the fourth power. Blue has the shortest wavelength, so it gets scattered the most, green somewhat less, yellow a little less, etc.
You have to add to this that the eye is most sensitive to green light, tailing off as you aproch blue (and Indigo and Violet) on one side and tailing off to yellow and orange and red on th other. So even though “indigo” and “violet” are shorter than blue, the sky isn’t violet because our eyes are so insensitive to it.
As an extra complcation, I note that the distribution of wavelengths is not uniform. There’s actually a lot more 4red than blue, and a lot more infrared than red, in sunlight. The atmosphere filters out some of this, but the disparity remains.
You can calculate the color of the lue sky – it’s a common exercise given to students of optics and colorimetry. See any book on color theory, or a comprehensive optics text, like Warren Smith’s Modern Optical Engineering. You can derive the blue color simply from the known solar output and the assumption of 1/(lambda)^4 scattering.