Why the sky is so blue, why is the sky blue

First of all, understand how light works, as light travels from the sun, it moves up and down like ocean waves, and when the wavelengths come together, we appear as if they are white.

In clear weather, there will be many tiny dust, water droplets, ice crystals and other substances in the air, when the sunlight passes through the air, the longer wavelength of the red light, orange light, yellow light in the sunlight can penetrate the atmosphere and directly hit the ground, and the shorter wavelength of blue, violet, indigo and other color light, is easily blocked by the particles suspended in the air, so that the light is scattered in all directions, making the sky appear blue.

The color of the sky is mainly the result of the interaction of sunlight with the atmosphere. Sunlight is white light, also known as polychromatic light (which contains all the colors of the rainbow), while the atmosphere contains a certain amount of water (usually a small amount) and ash particles.

When sunlight passes through an object, it is refracted at an angle in the direction of its propagation, depending on what kind of object it is passing through.

Transparent objects generally have a parameter called the refractive index, and the magnitude of this parameter depends on the color of the light rays passing through the object. So, when a beam of white light passes through an object, each color in that beam of light is refracted at a different angle, which is why the white light disperses into various colors after passing through the prism.

Each color in white light has its own wavelength. Blue has the shortest wavelength and the largest refractive index, i.e., it bends the most relative to white light, while yellow and red have the longest wavelength and the smallest bend angle, with little bending.

After the blue light is refracted and meets the tiny particles in the air, it refracts again, changes the direction of propagation, and zigzags forward in the atmosphere until it hits us. For this reason, when the light hits our eyes, it is as if the blue light is coming from all sides of the sky. Whereas, yellow and red rays are barely refracted, so the sun appears to us as yellow and red.

When the sun is not high in the sky but low in the sky, the sunlight passes through a thick atmosphere, and the light interacts with the tiny particles in the atmosphere many times, and the blue and purple rays travel in all directions, while the yellow and red rays still travel in a straight line from the sun, thus creating a beautiful scenery of the sunset on the earth.

Sunlight interacts with tiny particles.

When electromagnetic waves, such as sunlight, are incident in isolated atoms or small molecules, they interact with the electron cloud to transfer energy to the atoms. This causes the electrons in the atom to vibrate, and the electrons in the vibration do not remain for a long time, but release the energy they originally absorbed back to their original state.

This means that if the incident light is white (made up of colors of various wavelengths), the number of colors with the shortest wavelength (blue and violet) of the re-emitted white light is greater than the color with the longest wavelength (red and yellow). So we conclude that when sunlight encounters these tiny particles, most of the light they re-emit is blue and violet, so all we can see is blue.

Sunlight interacts with large particles.

When sunlight encounters large particles in the atmosphere, these large particles act like a mirror. The clouds in the sky are made up of these large particles, which are small droplets of water that have no color. When white sunlight hits these droplets, they act like mirrors to reflect or refract the light, while the color of the reflected or refracted light remains unchanged.

That's why we see white clouds floating in the blue sky.

Answer: Sunlight is composed of seven colors: red, orange, yellow, green, cyan, blue, and violet. The wavelengths of light in these seven colors are not the same. Dust and other particles in the atmosphere have a stronger ability to scatter light in short waves, while blue light has a shorter wavelength, so it is scattered when it reaches the atmosphere.

As a result, the sky appears blue. Using the phenomenon of "scattering", you can explain the following celestial phenomena:

For example, the sky above you is blue, but where the horizon meets heaven and earth, the sky looks almost white. Why? That's because sunlight travels a lot farther through the air than it does if it falls straight from the sky—and it grazes with many more particles along the way.

These large numbers of microparticles scatter light many times, so it appears white and light blue. It is recommended that you do a little experiment to verify this: take a glass of water, put it in a dark background, put a drop of milk, and then take a flashlight to one end of the cup, and close to it, the light of the flashlight will appear pale blue in the water.

If you put more milk into the water, the whiter the water will become, because the light is scattered again and again by these numerous milk particles, and the result is white. It's the same as being white above the horizon. Since 79% of the earth's surface is made up of oceans, it is reflected and refracted to form a blue color on the surface of the sky.

When sunlight enters the atmosphere, red light, orange light, yellow light and other long-wavelength color light can directly pass through the atmosphere to the ground, and blue light and other short-wavelength color light will be scattered, so that the sky is blue light in all directions.

Hope it helps.