säteilypainea

Säteilypainea, often translated as radiation pressure, is the mechanical pressure exerted by electromagnetic radiation. When light or other forms of electromagnetic radiation strike a surface, they transfer momentum. This momentum transfer results in a force on the surface, and when this force is distributed over an area, it manifests as pressure. The magnitude of this pressure depends on the intensity of the radiation and the reflective properties of the surface. Perfectly absorbing surfaces experience half the radiation pressure of perfectly reflecting surfaces.

The concept of radiation pressure was first theorized by James Clerk Maxwell in his theory of electromagnetism in the 19th century. It was experimentally confirmed by Pyotr Lebedev in 1900 and later by Ernest Nichols and Gordon Hull. While typically very small in everyday situations, radiation pressure plays a significant role in astrophysical phenomena. For instance, it is a primary factor in the formation of comet tails, pushing dust and gas away from the Sun. It also influences the structure and evolution of stars, counteracting gravity and preventing them from collapsing. In solar sails, the pressure from sunlight is harnessed to propel spacecraft through space, offering a propellant-free method of space travel.