The sky appears blue because of a phenomenon called Rayleigh scattering, where tiny molecules in the Earth's atmosphere scatter shorter, bluer wavelengths of sunlight more efficiently than longer, redder wavelengths. During sunsets, the sun's light has to travel through much more of the atmosphere, scattering away most of the blue and violet light, leaving the vibrant reds, oranges, and yellows to reach our eyes. No two sunsets are exactly alike due to variations in atmospheric conditions, including dust, pollution, and clouds, with higher clouds often contributing to more vivid displays.