Scattering of light occurs when light rays deviate from their original path after striking an obstacle like dust, gas molecules, or water vapors. Shorter wavelengths of light scatter more easily than longer wavelengths due to their waviness and increased chances of intersecting with particles. The scattering of blue light by fine atmospheric particles is why the sky appears blue. Without an atmosphere, there would be no particles for light to scatter off of, so the sky would appear dark.