Why is the sky blue? (This question is a bit silly ~ ~! ) Don't laugh at me! ! !

Why is the sky blue, not green or red?

First of all, you have to understand a truth: the things around us are colored only because the sun shines on them. Although sunlight looks white, all colors: red, orange, yellow, green, cyan, blue and purple exist in sunlight.

There are so many colors in the sky, why do I usually only see blue? You might ask.

If you think of light as a wave, you will solve the mystery. Light actually moves like a wave. Let's imagine a drop of rain falling in a puddle. When this drop of rain falls on the water, it will produce small waves, which will fall into a larger circle and spread in all directions. If these waves hit pebbles or other obstacles, they will bounce back and change the direction of the waves.

When the sun falls from the sky, it will continue to encounter some obstacles. Because the air that light must penetrate is not empty, it is made up of many tiny particles. Ninety-nine percent of them are either nitrogen or oxygen, and the rest are other gas particles and tiny floating particles, which come from automobile exhaust, factory smoke, forest fires or volcanic ash. Although oxygen and nitrogen particles are only one millionth of a drop of rain, they can still block the path of sunlight. The light bounced back from these small stumbling blocks and naturally changed direction.

But so many colors of light have changed direction, why only see blue? You probably still don't understand.

We must go back to the puddle we just talked about.

In a puddle, if a small wave meets pebbles, the water surface will be chaotic; But if it is a "huge wave", just like the kind of "huge wave" that you lift by hand at the edge of the puddle, it may simply overflow from the stone and reach the edge opposite the puddle unimpeded. Then, just like big waves and small waves, light waves of various colors also have different "waves", that is, wavelengths: but they are not like waves of water waves, and their size is invisible to the naked eye, because they are incredibly small, only 1% of a hair! You have to use very sensitive measuring instruments to measure accurately.

According to the determination of scientists, the wavelengths of blue light and purple light are relatively short, which is equivalent to "wavelet"; The wavelengths of orange light and red light are relatively long, which is equivalent to "big waves". When encountering obstacles in the air, blue light and purple light are "scattered" everywhere because they can't cross those obstacles, covering the whole sky-the sky, so they are "scattered" into blue.

The scientist who discovered this "scattering" phenomenon is called Rayleigh. He discovered it about 130 years ago, and he is also a Nobel Prize winner.

With the phenomenon of "scattering", the following astronomical phenomena can be explained:

For example, the sky above you is blue, but on the horizon, where heaven meets the earth, the sky looks almost white. Why? This is because sunlight travels far in the air from the horizon to where you are than it falls directly from the air-and it naturally eats more particles along the way. These large particles scatter light many times in this way, so it appears light blue in white. I suggest you do a small experiment to verify it: take a glass of water, put it in a dark background, put a drop of milk, and then illuminate one end of the cup with a flashlight and get close to it. The light of a flashlight will appear light blue in water. If you put more milk into water, the water will be whiter, because the light is repeatedly scattered by many milk particles, and the result is white. It is as white as the horizon.

When the sun goes down in the evening, the sky turns red instead of blue, and the setting sun turns dark red. Due to the countless particles that the sunset glow encountered on the way to your place, the purple and blue parts of the sunlight scattered in all directions, leaving only a little orange-red light visible to the naked eye-because of their long wavelength and "big waves", they crossed the obstacles on the road.

However, if you are careful, you will find that the sky will be dark blue for some time after sunset. This used to be a strange thing that scientists cared about, but several physicists solved the mystery 50 years ago: the blue color that caused the dusk sky was a special substance. This special substance gathers into a thick layer at a height of 20 to 30 kilometers from the earth's surface, which is called the ozone layer. This gas acts as a color filter for the falling sunlight: it intercepts the yellow and orange parts of the sunlight, but lets the blue part pass almost unimpeded. When the last light disappears, all the colors disappear in the night.

Ozone not only creates the blue sky at dusk, but also swallows a special kind of light that you can't see: ultraviolet light, or ultraviolet light. You must have heard how dangerous ultraviolet rays are to all living things, including you. If it shines on your bare skin for too long, you will get sunburned. The ozone layer everywhere is thick enough to intercept as much ultraviolet rays as possible: this is extremely important for all life on our planet.

Unfortunately, today, this life-threatening protective layer has become thinner in many places, and even a big hole has been formed over the South Pole. The killer of ozone destruction is "Freon"-a substance that people use to spray hair mousse or for refrigeration in refrigerators and air conditioners. This is a substance that is particularly harmful to the ozone layer, so many countries no longer use this "ozone killer".

Today we know why the sky in our eyes is blue. In fact, it is the same from the outside of the earth: the sea water covering two-thirds of our earth also emits blue light. Although there are brown land or green forests on the land, the sky is always blue-from the perspective of the universe, the whole earth is wrapped in a soft blue veil. Astronomers who have seen the earth from outside the atmosphere have reported this situation.

So it is absolutely right that the earth is called "blue planet". Its unique blue is the color of life.