Radiation pressure
The radiation pressure (ほうしゃあつ, radiation pressure) is pressure to act on the surface of the object catching the electromagnetic radiation. I am called radiation pressure, the light pressure in Japanese. As for the size of the radiation pressure, it is the value that fell below an incident energy flux density (energy to pass a unit area in a credit hour) at velocity of light when emission is absorbed to an object, and it is in the double value when emission is completely reflected. For example, the radiation pressure becomes ♠4.6µPa (when light of the sun is absorbed) because the energy flux density (solar constant) of the light of the sun at the position of the earth is ♠1366 W/m2.
Table of contents
Discovery
The fact that pressure acted on the plane of incidence when an electromagnetic wave hit the surface of the object was led theoretically in 1871 by James Clark Maxwell, and it was proved experimentally again by Ernst Fox Nichols and Gordon ferry Hull in 1901 in 1900 by Peter ニコラエヴィッチ rebbe demister. The radiation pressure is very weak, but can detect it when I put a feather made of the metal of the reflectivity in the state of the delicate balance and expose emission (Nichols radiometer).
Theory
The size of the radiation pressure to work on the surface of the object put in space met by the emission that is the same equal one is equal to 1/3 of the global radiation energy per unit volume of the space. Even if this uses whichever of electromagnetism, quantum mechanics, the thermodynamics, I can show it without assuming a property of emission oneself. In addition, the radiation pressure understands that I have a dimension same as a radiative energy density than this.
When an object is exposed to black body emission, and emission and the object surface are in thermal equilibrium state, the radiative energy density is equal to σT4 / 3c than a law of Stefan = Boltzmann (here as for σ in Stefan = Boltzmann constant, c in velocity of light, T absolute temperature of the space). 1/3 of this energy density becomes 6.305 *10-17 T4 J/(m3K4) in the international unit system. It becomes the size of the radiation pressure of the black body emission that this expressed in pascals.
Radiation pressure of the interplanetary space
In the interplanetary space in the solar system, overwhelming most of the radiative energy flux come from the sun. When emission is successful in this way only from one direction, the size of the radiation pressure becomes 3 times in case of the equal one emission namely σT4 / c. When an object completely reflects emission in addition to this, it becomes double namely 2σT4 / c more. The radiation pressure of the black body emission that water of the boiling point (T = ♠373.1 K) emits temperature as an example is about ♠3µPa. Thus, the radiation pressure to work for solar sailing to fly in the place is only about ♠22µPa when the radiation temperature at a certain place in the interplanetary space is equal to temperature of the boiling water. However, I can work as a big effect for the particles such as a gas ion or the electron in this way even if it is minute pressure. That is why the radiation pressure accounts for an important role by the theories of the electronic flow and comet material included in the solar wind.
Radiation pressure in the fixed star
The fixed star inside is very high in temperature. According to the current fixed star model, it is said that the central temperature of the sun surpasses approximately 1 billion K in the core of the supergiant star in approximately 15 million K. The strength of the radiation pressure is very important to the radiation pressure in such a high temperature environment to increase in proportion to the fourth power of the temperature. The radiation pressure is considerably still in comparison with gaseous pressure small in the sun, but radiation pressure carries most of the pressure of the star in the large mass star.
Solar sailing
The solar sailing suggested for one kind of the promotion mechanism of the space machine uses radiation pressure from the sun as power. Cosmos 1 launched in 2005 by association of planet was equipped with solar sailing (the display ends in failure). IKAROS which I launched in JAXA in 2010 became the world's first solar sailing proof machine.
References
- van Nostrand. Scientific Encyclopedia (3rd ed.).
This article is taken from the Japanese Wikipedia Radiation pressure
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