Light (pressure of)

Light (pressure of)

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When a light wave strikes a body, it transmits a certain energy or, as it is said in physics, a certain amount of movement, thus exerting pressure.

In astronomy this phenomenon has its strong demonstration in the tails of comets that, as is known, are composed of tiny particles of dust and gas. The radiation pressure of the Sun has its maximum effect on particles of dimensions corresponding to the wavelength of the light itself, that is, on the dust grains with a diameter of a few microns (microns = millionths of a millimeter).

The effect of light pressure on cometary tails explains the phenomenon by which, in the vicinity of the Sun, the tails themselves are arranged in an antisolar direction instead of directing them towards the Sun itself, as would be expected if the only force that act out the attraction of our star. On the other hand, in this case, the pressure exerted by the light overcomes the force of solar attraction.

An astronautic application of the light pressure is given by the solar sailing spacecraft. It is a true cosmic sailboat that moves in space not by virtue of the thrust of a rocket engine, but that of light.

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