Radiation pressure

Radiation pressure is the pressure exerted upon any surface exposed to electromagnetic radiation. Radiation pressure implies an interaction between electromagnetic radiation and bodies of various types, including clouds of particles or gases. The interactions can be absorption, reflection, or some of both (the common case). Bodies also emit radiation and thereby experience a resulting pressure.

The forces generated by radiation pressure are generally too small to be detected under everyday circumstances; however, they do play a crucial role in some settings, such as astronomy and astrodynamics. For example, had the effects of the sun's radiation pressure on the spacecraft of the Viking program been ignored, the spacecraft would have missed Mars orbit by about 15,000 kilometers.

This article addresses the macroscopic aspects of radiation pressure. Detailed quantum mechanical aspects of interactions are addressed in specialized articles on the subject. The details of how photons of various wavelengths interact with atoms can be explored through links in the See also section.

Johannes Kepler put forward the concept of radiation pressure back in 1619 to explain the observation that a tail of a comet always points away from the Sun.

The assertion that light, as electromagnetic radiation, has the property of momentum and thus it exerts a pressure upon any surface it is exposed to was published by James Clerk Maxwell in 1862, and proven experimentally by Russian physicist Pyotr Lebedev in 1900 and by Ernest Fox Nichols and Gordon Ferrie Hull in 1901. The pressure is very feeble, but can be detected by allowing the radiation to fall upon a delicately poised vane of reflective metal in a Nichols radiometer (this should not be confused with the Crookes radiometer, whose characteristic motion is not caused by radiation pressure but by impacting gas molecules).

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