Hii

Both of these are the examles of phenomenon called Scattering of Light.
When light passes through certain particles which have size comparable to wavelength of light, then the path of light gets deviated in all possible directions. This is what is called scattering of light.
Now we have different colors in light and all these colors have different wavelengths and so there deviation varries.
The red color has the maximum wavelength and so it gets scattered the least when the rays from the sun travel longer distance during sunset and sunrise hence giving reddish- orange look to the sun during sunset and sunrise.
The blue light has less wavelength and so it scattered the most giving blue color to the sky. The deviation of this light takes place due to the particles present in the atmospheres, the clouds etc and so we see sky as blue in color.

Hope this helps
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