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Asked by anon-267411 on 5 Nov 2020. This question was also asked by anon-267532, anon-267551.
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Patrick Dalton answered on 5 Nov 2020:
When light from space reaches Earth it hits our atmosphere. The atmosphere cause the light to scatter in all directions, but it scatters mainly blue and purple. (This process is known as Rayleigh scattering.)
If the light from our sun contained an even mixture of all the colours the sky might appear more so purple than blue, but there isn’t really that much purple light to be scattered in the first place, so we see it during the day as a shade of blue.
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Bradley Young answered on 5 Nov 2020:
Interestingly, this is why the sun looks yellow too, because the blue light is scattered away like Patrick says, and then the yellow light is what’s left over, so the sun looks yellow.
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Daisy Shearer answered on 6 Nov 2020:
The sky is blue because of something called ‘Rayleigh scattering’. It happens because light from the sun hits particles in the Earth’s atmosphere which have a size smaller than the wavelength of the light from the sun. Small particles in the atmosphere scatter blue light much more strongly than other wavelengths of visible light (because blue and purple light have the smallest wavelengths in the visible spectrum), so that’s why we see it as blue when it hits our eyes. Scattering of light also explains why clouds are white. In this case, the mechanism is called ‘Mie scattering’ and it happens when the particles being hit by sunlight are big compared to the wavelength of light. This is the case with water droplets in clouds. Rather than scattering blue light more strongly, the droplets scatter all the visible wavelengths with the same strength, resulting in a white colour.
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