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Asked by anon-384286 on 15 Mar 2024.
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Sharron Kenny answered on 15 Mar 2024:
the sky appears blue because of how it reflects and absorbs wavelengths of light
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Caroline Roche answered on 7 Jun 2024:
When the white light from the sun passes through atmosphere the light is scattered, we usually see blue as it has a shorter wavelength than the other colours. Light is scattered differently under different conditions which is why we see a red sky sometimes during sunset.
It’s a popular question, NASA has a webpage dedicated to it:
https://spaceplace.nasa.gov/blue-sky/en/
Comments
Andrew M commented on :
As Sharron says, it’s due to scattering and absorption of the light from the sun. How well light is scattered from particles depends on the optical properties of those particles and their size. As the size of the particles drop below the wavelength of the light, their scattering ability starts to fall very rapidly. Red light has a longer wavelength than green light, and green light has a longer wavelength than blue light so for the very small particles in the atmosphere red light is scattered very weakly, green a bit stronger and blue much more strongly than red. Absorption by oxygen then takes out the deep blues leaving lighter blue and a touch of green to colour the sky.
DON’T LOOK AT THE SUN! Closer to the position of the sun the colour changes because transmission, the passing of light through the atmosphere, matters more than scattering, so you see more red light in the mix, giving a yellowish tinge. At dawn and dusk the sunlight has to travel through more of the atmosphere and thicker air closer to the ground, so the balance of scattering and transmission changes again, with more of the blue being lost to scattering and the reds passing through.
The effects are known as Rayleigh Scattering.