Why is the sky blue
The answer to this question was given in 1899 by John Rayleigh (John Strutt, 3rd Baron Rayleigh). The sun emits light. The human eye perceives the sunlight as "white." To be more precise - colorless. In fact, the "white" light is composed of a mixture of colored light. If you miss the beam of "white" light through a prism, we get a rainbow, which is called the spectrum. Glass prism decomposes white light 7 colors: red, orange, yellow, green, blue, indigo, violet.
In fact, the color tones much more, but scientists have agreed to allocate only 7 basic colors. Decomposition of the spectrum, least of all deviates a beam of red light (it has the largest wavelength). The ray of violet colour deviates more than other rays (he has a shorter wavelength).
In 1869, a scientist from England, John Tyndall tried to answer the question "Why is the sky blue". He said that in the Earth's atmosphere is very much small particles of dust, water, ice. These particles absorb longer wavelengths (red part of the spectrum), but missing the short wave (the blue part of the spectrum).
In his laboratory, the English scientist has created a model of smog. When John highlighted could beam of white light, was able to turn blue. Tyndall concluded - to clean the earth's atmosphere the sky should be white.
In 1899, John Rayleigh refuted the hypothesis of his colleagues and gave a more complex, but more truthful theory.
Sunlight - is the smallest particles (photons), which emits sun. The photons travel at the speed of 300 000 km/s. Photons have a different wavelength (spectrum), summed, they form white light. The Earth's atmosphere composed of various gases: oxygen, hydrogen, nitrogen and others. In the outer space there is no gas (vacuum), so that the sunlight is not scattered in space and is not absorbed.
Photons if it enters the Earth's atmosphere collide with molecules of the gas (argon, oxygen, hydrogen, etc.), And the white light is dispersed. The red component of the spectrum (wavelength) is scattered in 8 times worse than the blue component of the spectrum (short wave). For this reason, after dispersion in the air is 8 times more blue than red.
Despite the fact that most of the scattered purple spectrum component due to mixing purple and green waves of the sky seems blue. In addition, the human eye perceives the color blue is better than purple.