The absorption and prompt re-emission of a photon by a particle, with a change of direction but not normally any significant change of energy (wavelength). The type of scattering depends on the particle involved, which can be an electron, a molecule, or a dust speck. If the particle is a free electron, the photon suffers Thomson scattering; the Compton effect is the same phenomenon but involving high-energy photons (X-rays and gamma rays) with a change of photon energy. If the scatterer is a bound electron (i.e. within an atom or molecule), the photon undergoes resonant scattering. If the particle is small compared with the wavelength, the photon suffers Rayleigh scattering; in this case the particles causing the scattering are molecules and dust, either in the Earth’s atmosphere or in space. Alternatively, if the particle is large compared with the wavelength, the photon undergoes Mie scattering; this can be caused by atmospheric and interstellar dust. The types of scattering differ in their probability of occurrence at different wavelengths, and in the preferred direction of the outgoing photons.