Rayleigh scattering

elastic scattering of light, or other electromagnetic radiation, by particles of size much smaller than the wavelength of the radiation

Rayleigh scattering is the way that light scatters when it hits a very small object. This theory is valid if the wavelength of the light is much bigger than the object. It is named after Lord Rayleigh but was also the work of Raman and Krishnan as it is part of the Raman scattering theory.