What does sunset looks like from outer space?
One can think of it as a ring of red light that ceaselessly circles the earth.
The sunlight, in contact with the atmosphere, goes through a process called Rayleigh diffusion.
It occurs when a light wave collides with particles, small in size compared to its wavelength, which become sources of new wave fronts.
The electric charges of the molecules move in response to the oscillating electric field of light (composed of moving magnetic and electric fields), and become in turn the sources of other spherical electromagnetic waves.
It is this process that is the reason why air molecules mainly scatter the blue component of sunlight, making the sky the same color.
But when the sun’s rays arrive diagonally on the surface, they are forced to pass through a greater amount of air, which diffuses more blue light, so that only the red component remains of the incoming light, which is precisely what characterizes the sunset and sunrise.