Young Brunette Girl On The Sand At Sunset

Rayleigh scattering is the elastic scattering of electromagnetic radiation due to the polarizability of the electron cloud in molecules and particles much smaller than the wavelength of visible light. Rayleigh scattering intensity is fairly omnidirectional and has a strong reciprocal 4th-power wavelength dependency and, thus, the shorter wavelengths of violet and blue light are effected much more than the longer wavelengths of yellow to red light. During the day, this scattering results in the increasingly intense blue color of the sky away from the direct line of sight to the Sun, while during sunrise and sunset, the much longer path length through the atmosphere results in the complete removal of violet, blue and green light from the incident rays, leaving weak intensities of orange to red light.
After Rayleigh scattering has removed the violets, blues, and greens, people's viewing of red and orange colors of sunsets and sunrises is then enhanced by the presence of particulate matter, dust, soot, water droplets (like clouds), or other aerosols in the atmosphere, (notably sulfuric acid droplets from volcanic eruptions). Particles much smaller than the wavelength of the incident light efficiently enhance the blue colors for off-axis short path lengths through air (resulting in blue skies, since Rayleigh scattering intensity increases as the sixth power of the particle diameter). Larger particles as aerosols, however, with sizes comparable to and longer than the wavelength of light, scatter by mechanisms treated, for spherical shapes, by the Mie theory. Mie scattering is largely wavelength insensitive. Its spacial distribution is highly preferential in the forward direction of the incident light being scattered, thus having its largest effect when an observer views the light in the direction of the rising or setting Sun, rather than looking in other directions. During the daytime, Mie Scattering generally causes a diffuse white halo around the Sun decreasing the perception of blue color in the direction toward the Sun and it causes daytime clouds to appear white due to white sunlight. At sunset and sunrise, Mie scattering off of particles and aerosols across the horizon, then transmits the red and orange wavelengths that remain after Rayleigh scattering has depleted the blue light. This explains why sunsets without soot, dust, or aerosols are dull and fairly faint red, while sunsets and sunrises are brilliantly intense when there are lots of soot, dust, or other aerosols in the air.
Sunset colors are typically more brilliant than sunrise colors, because the evening air contains generally more particles and aerosols and clouds than morning air. Cloud droplets are much larger than the wavelength of light; so they scatter all colors equally by Mie scattering, which makes them appear white when illuminated by white sunlight during the daytime. The clouds glow orange and red due to Mie scattering during sunsets and sunrises because they are illuminated with the orange and red light that remains after multiple prior Rayleigh scattering events of the light from the setting/rising sun.