In astronomy and physics, radiation pressure is pressure exerted upon a surface exposed to electromagnetic radiation. The pressure is the power flux density divided by the speed of light if it is absorbed. If the radiation is reflected, the radiation pressure is doubled. Radiation pressure is about 10−5 Pa at Earth’s distance from the Sun and decreases by the square of the distance from the Sun. Though weak, such pressures produce significant effects on small particles like ions, electrons and cometary dust particles.