Säteilypaineen

Säteilypaineen, or radiation pressure, is the mechanical pressure exerted by electromagnetic radiation. When light or other forms of electromagnetic radiation strike a surface, they transfer momentum, resulting in a force. This force, distributed over an area, constitutes radiation pressure.

The magnitude of radiation pressure depends on the intensity and absorption or reflection properties of the surface. For a perfectly absorbing surface, the pressure is equal to the energy density of the radiation. For a perfectly reflecting surface, the pressure is twice that value, as the radiation experiences a change in momentum twice as large. While typically very small in everyday situations, radiation pressure plays a significant role in astrophysical phenomena.

In stars, radiation pressure is crucial in counteracting the inward pull of gravity. The immense energy generated by nuclear fusion creates outward-directed photons, whose pressure prevents the star from collapsing. Without this outward pressure, stars would not be able to maintain their structure and stability.

Cosmic dust and gas clouds are also influenced by radiation pressure from nearby stars or galaxies. This pressure can push particles away, shaping nebulae and influencing the formation of planetary systems. Furthermore, the tails of comets are largely formed by the interaction of solar radiation pressure and the solar wind, which push away the vaporized material.