Evan Michael

“The shorter wavelengths, those that we sense as violet and blue light, are more efficiently scattered than the longer wavelengths—those that we sense as orange and red light. When we look up on a cloudless day and admire the blue sky, we are witnessing the preferential scattering of the short waves in sunlight. ...
So why is the sunset red? The red of the sunset is what's left of sunlight after the air scatters the blue away. Since the atmosphere is a thin shell of gravitationally bound gas surrounding the solid Earth, sunlight must pass through a longer slant path of air at sunset (or sunrise) than at noon. Since the violet and blue waves are scattered even more during their now-longer slant path through the site than when the Sun is overhead, what we see when we look towards the sun is the residue—the waves of sunlight that are hardly scattered away at all, especially the oranges and reds. A blue sky makes a red sunset.”
― Carl Sagan, Pale Blue Dot: A Vision of the Human Future in Space