radiation pressure

The pressure exerted by a stream of photons when they are transferring momentum to matter. In astronomy, radiation pressure is important wherever the flux of radiation is extremely high, for example in the outer layers of a star. In the interstellar medium, radiation pressure on dust grains can be more important than the local gravitational field. Within the solar system, the pressure of radiation from the Sun acts to push the smallest particles outwards. Poynting-Robertson effect.