More sunlight shines on the earth through the atmosphere, but nothing is very

The sky we see is often blue, especially after a heavy rain, as blue as autumn water, which makes people feel relaxed and eager to fly. Why is the sky blue?

The atmosphere itself is colorless. The blue of the sky is a picture created by atmospheric molecules, ice crystals, water droplets and sunlight.

When sunlight enters the atmosphere, long-wavelength colored light, such as red light, has great transmission power and can penetrate the atmosphere and shoot to the ground; However, violet, blue and cyan light with short wavelength will be easily scattered when it touches atmospheric molecules, ice crystals and water droplets. Scattered purple, blue and cyan light spread all over the sky, making the sky appear blue.

Why is the sky blue, not green or red?

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

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

If you think that light is 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 turn into larger circles 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 shines from the sky, it will constantly 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.

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 mentioned just now.

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 one you hold up by the puddle, it may simply overflow from the stone and reach the opposite edge of the puddle unimpeded. Then, just like there are big waves and small waves, light waves of various colors also have different "waves", that is, wavelengths: but unlike waves of water waves, the size cannot be seen by the naked eye. Only very sensitive measuring instruments can accurately measure.

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, covering the whole sky-the sky, so they are "scattered" into blue.

The scientist who discovered this scattering phenomenon was Rayleigh, who discovered this phenomenon 30 years ago. 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 and earth meet, the sky looks almost white. Why? This is because sunlight travels far from the horizon to your place in the air than it falls directly from the air-naturally, along the way, it also sweeps more particles. These large particles scatter light many times, so they look pale 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. Close to it, the light of the flashlight will appear light blue in the water. If you put more milk into the water, the water will be whiter, because the light is repeatedly scattered by many milk particles, and the result is white. The reason is the same as that the horizon is white.

When the sun goes down in the evening, the sky turns from blue to red, and the setting sun turns dark red. This is also the case. As the sunset met many particles on the way to your place, the purple and blue parts of the sun 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 appear dark blue for a period of time after sunset. This used to be a strange thing that scientists paid attention to, but several physicists have solved the mystery 50 years ago: the blue of the sky at dusk is a special substance. This special substance gathers in a thick layer at a height of 20 to 30 kilometers from the earth's surface. It 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, of course). If it shines on your bare skin for too long, you will get sunburned. The ozone layer everywhere is thick enough to block 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 ozone killer is "Freon", which is 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.

Therefore, it is completely correct that the earth is called the "blue planet". Its unique blue is the color of life.

And:

The clear sky is blue, not because the atmosphere itself is blue, nor because it contains blue substances, but because atmospheric molecules and tiny particles suspended in the atmosphere scatter sunlight.

Due to the inhomogeneity of the medium, the phenomenon that light deviates from the original propagation direction and scatters sideways is called the scattering of light by the medium.

The scattering of fine particles follows Rayleigh's law: the intensity of scattered light is inversely proportional to the fourth power of wavelength.

When sunlight passes through the atmosphere, violet light, blue light and cyan light with shorter wavelength are most easily scattered, while red light, orange light and yellow light with longer wavelength are less scattered. Due to this comprehensive effect, the sky appears blue.

Why is the rising sun red? In the morning, sunlight passes through the thick atmosphere. At this time, violet light and blue light are strongly scattered. When they reach the horizon, there is very little left, only yellow light, orange light and red light with longer wavelength are left. So the rising sun is red.

Why is the sky blue?

The blue sky we see is the result of selective scattering of visible light in incident solar radiation by air molecules and other particles. The scattering intensity is related to the particle size. When the particle diameter is smaller than the wavelength of visible light, the scattering intensity is inversely proportional to the fourth power of the wavelength, and light with different wavelengths is scattered in different proportions, which is also called selective scattering. When visible light radiated by the sun enters the atmosphere, air molecules and particles (dust, water droplets, ice crystals, etc. ) will scatter sunlight around. Among the seven kinds of light that make up sunlight, the wavelength of red light is the longest and that of violet light is the shortest. The red light with longer wavelength has the highest transmittance, and most of it can directly penetrate the particulate matter in the atmosphere and reach the ground. Blue light, indigo light and violet light with shorter wavelength, etc.

If the light with short wavelength scatters more strongly, you will definitely ask why the sky is not purple. One of the reasons is that when the visible light radiated by the sun passes through the atmosphere, the absorption rate of violet light by air molecules is stronger, so there is less violet light in the visible light radiated by the sun, but it is not absolutely absent. We can easily observe the purple light in the rainbow after the rain. Another reason is related to our eyes themselves. In our eyes, there are three types of receptors, called red, green and blue cones, which are only sensitive to the corresponding colors. When they are stimulated by external light, the visual system will reconstruct the color of these lights according to the stimulation intensity of different recipients, that is, the color of the objects we see. In fact, red cones and green cones are very sensitive to blue and purple.

Answer 1: The sky we see is blue on a sunny day. You may notice that sometimes after a heavy rain, the sky becomes particularly blue, and the clearer the weather, the bluer the sky. There is a simple reason. The scattering of sunlight by the atmosphere makes the sky look blue. The surface of the earth is surrounded by the atmosphere. When sunlight enters the atmosphere, air molecules and particles (dust, water droplets, ice crystals, etc. ) will scatter sunlight around. Sunlight consists of seven kinds of light: red, clear, yellow, green, blue, indigo and purple, of which red light has the longest wavelength and violet light has the shortest wavelength. Red light with relatively long wavelength has the highest transmittance, which can directly penetrate the particulate matter in the atmosphere and reach the ground, while blue light, indigo and violet light with short wavelength have the highest transmittance. The scattered light waves are also the most, so the sky we see is blue. In fact, the sky has always been blue. You can see the blue sky almost every day on the plateau. It's windy and dusty in spring, cloudy in summer and foggy in winter, which makes it impossible for us to see the blue sky often. Only in autumn, the air is clean, which gives us many opportunities to see the blue sky. Answer 2: When sunlight enters the earth's surface through the atmosphere, air molecules or other particles (such as water droplets, suspended particles or air pollutants) in the atmosphere will absorb, scatter, reflect and transmit sunlight, thus forming the brilliant afterglow of blue sky, white clouds or sunset. On a planet without an atmosphere, the sky will be dark even during the day. The blue sky we see is the result of selective scattering of incident sunlight by air molecules. The scattering amount has a great relationship with the particle size. When the spot diameter is smaller than the wavelength of visible light, the scattering amount is inversely proportional to the fourth power of the wavelength, and the proportion of light scattered at different wavelengths is different, which is also called selective scattering. Compared with blue light (wavelength =0.425μm) and red light (wavelength =0.650μm) in the incident solar spectrum, blue light scattered by air particles is about 5.5 times more than red light when passing through the atmosphere. Therefore, on a clear day, the sky is blue. However, when there is fog or thin clouds in the sky, because the diameter of water droplets is larger than the diameter of visible light waves, the role of selective scattering no longer exists. At this time, all wavelengths of light will be evenly scattered, so the sky is white. Facing the white clouds in the clear sky, the diameter of the cloud drops in the clouds is larger. When sunlight hits it, it is not scattered but reflected, so it looks whiter and brighter. A problem with the ground as the reference starting point, because the universe is an infinite space, the farthest edge of the universe (limited universe) that we can observe at present is estimated to be150-200 billion light years, and the sky height that can be observed according to the current scientific and technological level is temporarily this value. In other words, the sky is infinitely high, as high as you want.