In principle, only small children ask such a question, while adults simply perceive everything as it is. But what is the answer to the child? Not everyone knows why the sky is blue and the grass is green))) So let's try to figure it out, at least with one natural phenomenon?
Indeed, why is the sky blue, if this is the same air that we see around us and that we breathe. Is it colorless and the sky is blue?
And what happened, it turns out that the answer to this question is very difficult - many great scientists searched, experimented and racked their brains in search of an explanation and understanding of the celestial phenomenon.
But at the same time, just over 100 years (1899) ago, the English scientist - physicist Lord D. Rayleigh offered the best explanation for this phenomenon.
To do this, first, it is necessary to determine the next moment, the sun radiates and sends pure white light to the earth. Which suggests that the color of the sky should be white, like light. What happens to the light on its way to Earth, that it becomes different, and we see the blue sky. So, white light is a bundle of colored rays, that is, it consists of 7 colors: red, orange, yellow, green, cyan, blue and violet. And by connecting them together we get white light. How is it that light decays and why do we only see blue?
The first assumption was that the air that surrounds the Earth is a mixture of gases: oxygen, nitrogen, argon, etc. Ice crystals and water vapor are also present in the earth's atmosphere, and dust and other small particles are suspended in the air. And in the upper layers of the earth's atmosphere there is a layer of ozone. Therefore, some scientists believed that water and ozone molecules absorb red rays and transmit blue rays. But according to calculations, it turned out that the earth's atmosphere simply does not have enough water and ozone to give the sky a blue color.
The Englishman John Tyndall suggested in 1869 that dust and other particles scatter light. That is, since blue light (ray) is scattered to the least extent, and passing through layers of various particles, it reaches the Earth and creates a blue sky phenomenon. In his laboratory, a scientist conducted an experiment, he created a model of smog and illuminated it with a very bright white light, the smog turned blue. Therefore, John Tyndall suggested that if the air of our Earth were clean, then we would have a bright white sky, since nothing would scatter white light.
And, Lord Rayleigh also thought so, though not for long. In 1899, D. Rayleigh published his explanation: that it is air, and not smoke, smog or dust, that colors the sky blue.
It turns out that part of the sun's white rays passes between gas molecules without coming into contact with them, and without the slightest changes reach the surface of our Earth. The other part, while the greater part, is absorbed by gas molecules. When photons come into contact, the molecules are charged with energy and excited, and then they emit energy in the form of the same photons. These secondary photons can be of any color, since they have different wavelengths - from red to violet. They scatter in all directions: towards the Sun, and to the sides, and towards the Earth.
Lord - scientist D. Rayleigh suggested that the color of the emitted ray depends on the predominance of quanta of one color or another in the ray. When a gas molecule collides with photons of the sun's rays, there are eight blue quanta for one secondary red quantum.
Conclusion: Intense blue light literally pours on us from all sides from the billions of gas molecules in the atmosphere. This light is mixed with photons of other colors, so it does not have a pure blue tone, that is, the light beam passes through the "filters" of the earth's atmosphere and creates a blue sky.
This is how you can simply answer the child's question: the sky is blue because the white light of the sun has different colors, and only blue breaks through the earth's atmosphere.