Why is the sky blue during the day and black at night?

The color of the sky during the day is completely determined by the processes of scattering of solar radiation in the Earth’s atmosphere. Short-wave radiation (blue part of the spectrum) is scattered more than long-wave radiation (red part of the spectrum). Therefore, during the day, scattered radiation, in which the blue color predominates, falls into the observer’s eye from different directions (the main part of the long-wavelength radiation, that is, orange and red light, without scattering, falls on the Earth’s surface or leaves the atmosphere). As a result, the sky is blue. And at night, when sunlight does not enter the atmosphere on the side of the observer, there is no scattered radiation – the sky becomes black.

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