Why the sky is blue?

"There was a theory that the sky color coincides with the color of air or any gas included in its composition. Isaac Newton first realized that if it were so, then the white sun, the moon and the tops of the snowy mountains would also see the blue, like through the colored glass. He proved that the air does not have color. Opening the decomposition of white light on color components, he successfully explained the origin of the rainbow decomposition of light on water droplets.

His attempt looks like a blue sky of the sky turned out to be erroneous.

In 1869, the Englishman John Tyndal conducted an experiment and demonstrated that if artificially created fog would highlight white light beam, then he will look blue on the side. So it became clear that the whole thing is in the scattering of light. In fact, it was enough to look at the blue smoke from the burning end of cigars, cigarettes or cigarets. Indeed, since ancient times, people were known that the beam of light spread straight. However, he is always visible if you look at it on the side. But usually the beam seems white.

An explanation was found in 1871 with a wonderful physicist Lord Ralel (John Strett). It calculated that if the light dissipates on large particles, for example on dusting, the size of which is significantly larger than the wavelength of any of the components of white light, then it remains white.

For example, it will be if the size of the dust comparable with one micrometer. But if the size turns out to be much less, then blue and purple will begin to dissipate much stronger than red. It means scattered light, painting the sky, will be blue. The theory perfectly explained why the sun at sunrise and sunset is red: all due to the fact that the beam has to pass thicker layers of air, blue color dissipates even stronger, and red gets into the eye directly. That’s just embarrassed that the sky is blue just in those places where there is no dust. What then the light is scattered? Rileu suggested that on air molecules.

In 1906, the experiments of the American astrophysics of Charles Abbot on the scattering of light allowed us to estimate the concentration of molecules in the air, and it perfectly coincided with the already known from the very other experiments. However, joy continued not long. In 1907, the our professor of physicists Leonid Mandelshtam, who was only 28 years old, noticed that the theory of Rayleigh works if the number of molecules in the air volume unit is quite small, and in the real atmosphere it is not. The blue of the sky again became inexplicable until Mandelstam understood: the thing is that the air is never homogeneous. Always due to the random thermal movements of molecules in very small air volumes, random changes of density are formed. That’s why there is scattering, giving the sky blue.

All is well, and you could calm down. But these random fluctuations according to the calculation should lead to very small, difficult to measure the flicker of the sky. The experience that would allow to prove that it should be so mandelles, together with his colleague, Gregory Landsberg was able to prepare only after 18 years. It turned out to be very subtle, conscientious experience, as a result of which a completely new phenomenon was opened, obtained the name of the combinational scattering. For many years, it determined the development of optics and eventually influenced the opening of lasers. But this is another conversation. It is important that a strong scientific result not only responds to the questions raised, but also necessarily gives rise to new, even more difficult and interesting ".