Sunset

Sunset, also called sundown, is the disappearance of the Sun below the horizon due to the rotation of the Earth, occurring roughly every 24 hours everywhere except near the poles; the astronomical moment is marked when the upper edge of the solar disk passes below the horizon. Near the horizon, atmospheric refraction bends light so the sun remains visible slightly after it is geometrically below the horizon, and this refraction also distorts its shape, making it appear wider than it is tall. As sunlight travels through more atmosphere at low angles, Rayleigh scattering removes shorter blue and green wavelengths more strongly, leaving the orange and red hues typical of sunsets, with the reddened light further scattered by cloud particles through Mie scattering; sunset colors are typically more vivid than sunrise colors because the evening air usually holds more particulates than the morning air.