The sky is blue physics. How to explain to a child why the sky is blue. Separation of the atmosphere into layers depending on their electrical properties

There are millions of questions that, being children, we do not receive an answer, and when we grow up, we are simply embarrassed to ask. One of these unanswered questions: "why is the sky blue?" And everything would be fine, and without this knowledge you can live, but when a child begins to ask such tricky questions to his parents, they often become ashamed, and they begin to change the subject. Then the child grows up not knowing the answer, he has his own children and everything repeats again. Let's break this "vicious circle" and understand the reasons why the sky is blue. Consider the issue from all possible points of view.

The phenomenon of blue sky in terms of physics

Let's get straight to the point, the sky is blue because the earth's atmosphere scatters the light of the sun. All research conducted over the past 200-300 years comes down to this. Consider a few axioms that affect the blue sky phenomenon:

1. The white light of the sun is a combination of different color streams. White color "separately" does not exist. As everyone knows, there are only 7 colors (red, orange, yellow, green, blue, blue, purple), the rest of the colors are obtained only when they are combined. White color is obtained by combining all seven colors. It is worth considering that it is precisely the colors that we can distinguish with the eye that are meant.
2. The atmosphere is not empty, it consists of many gases: nitrogen (78%), oxygen (21%), carbon dioxide, water in its various states (steam, ice crystals). There is also a lot of dust around us, elements of various metals. All of them distort the white light of the sun.
3. The air that surrounds us and that we breathe is actually opaque. In any case, in large quantities. We do not live in a vacuum, after all.

From these three facts we will proceed further.

History

Back in the 19th century, a scientist named John Tyndall conducted research that proved that we see the sky blue because of particles in the atmosphere. In his laboratory, he artificially created a fog with dust particles and directed a bright white beam at it - the color of the fog changed to bluish. 30 years later, in 1899, the physicist Rayleigh refuted the research of his predecessor and published evidence that the sky is blue because of air molecules and no dust in it. This phenomenon is called diffuse sky radiation You can read more about this on Wikipedia.

The sky looks blue because air scatters short wavelength light more than long wavelength light. Since blue light has a shorter wavelength, at the end of the visible spectrum, it scatters more in the atmosphere than red. (Source: Wikipedia)

What is light? Light is a stream of photons, some we can see with our eyes and some we can't. So, for example, we see the standard spectrum of colors, but the ultraviolet, which also emits the sun, does not. What color we see in the end depends on the "wavelength" of this stream. This wavelength determines what color you get.

So. We have determined that the sun sends us quanta with a wavelength that corresponds to white, but how does it turn into blue as it passes through the atmosphere? Let's take the example of a rainbow. Rainbow - is a direct example of the refraction of light and its division into a spectrum. You can create your own rainbow using a glass prism at home. The decomposition of color into a spectrum is called dispersion.

So, our sky functions as a prism. Most white light changes its wavelength as it passes through gas molecules in the atmosphere. As a result, photons “leaving” the molecules have a different color. This color can be either purple, red, or blue and blue.

Why do we see blue and not red?

What color we eventually see when light travels from the sun to the earth depends on which photons prevail. For example, when light passes through the atmosphere, the number of blue color quanta is 8 times more than red, and violet is 16 times! This is due to the very different wavelength, so violet and blue scatter strongly, and red and yellow scatter much worse. Based on this theory, the sky should be purple, but it is not. This is due to the fact that purple is much worse perceived by the human eye, unlike blue. That's why the sky is blue.

Video about why the sky is blue:

Why is the sky blue during the day and the sunset is red

Everything, again, is connected with the dispersion of color. The angle of incidence of solar white light becomes smaller, and the light passes through more air molecules, the wavelength of light increases. This amount is enough to diffuse to red.

The answer to the question why the sky is blue for children

If a child asked you a question about the blue sky, you certainly will not tell him about dispersion, spectra and photons. It is enough to quote from the children's book "100 Children's Why" Tatiana Yatsenko:

Usually we draw the sun's rays in yellow. But in fact, the light of the sun is white and consists of seven colors. These are the colors of the rainbow: red, orange, yellow, green, blue, indigo, violet. Not all colors pass through the air, only blue, indigo and violet. They color the sky.

This will be enough. On our website, you can also download a presentation on the topic: “Why the sky is blue” at the link: It may come in handy in the classroom at school.

In simple terms, the sky is blue, because when light is decomposed, violet scatters the most, and red the least.

Light through a prism

As you know, white light consists of seven primary colors that change as the wavelength of light decreases: red, orange, yellow, green, blue, indigo and violet. And, for example, astronauts in orbit see a dazzling white Sun against a black sky. This is how it should be: the components of white light reach them in the vacuum of space without distortion, while they reach the Earth through the "filter" of the atmosphere.

In more detail, you need to understand what is diffuse sky radiation- solar radiation reaching the earth's surface after it has been scattered by molecules or solid particles in the atmosphere. Of all the radiation from the Sun that scatters in the atmosphere, about two-thirds eventually reaches the Earth as diffuse radiation (if the Sun is high above the horizon, at least 25% of the incident radiation is scattered).

The main mechanisms of light scattering in the atmosphere (Rayleigh scattering, Mie scattering) are elastic, that is, in this case, the direction of radiation changes, without changing the wavelength.

The sky looks blue because air scatters short wavelength light more than long wavelength light. The intensity of Rayleigh scattering due to fluctuations in the number of air gas molecules in volumes commensurate with the wavelengths of light is proportional to 1 / λ 4, λ is the wavelength, i.e. the violet part of the visible spectrum is scattered approximately 16 times more intensely than red. Since blue light has a shorter wavelength, at the end of the visible spectrum, it scatters more in the atmosphere than red. Due to this, the part of the sky outside the direction of the Sun has a blue color (but not violet, since the solar spectrum is uneven and the intensity of the violet color in it is less, and also due to the less sensitivity of the eye to violet and more to blue, which irritates not only those sensitive to blue cones in the retina, but also sensitive to red and green light).

During sunset and dawn, light travels tangentially to the earth's surface, so that the path traveled by light in the atmosphere becomes much longer than during the day. Because of this, most of the blue and even green light is scattered from direct sunlight, so the direct light of the sun, as well as the clouds it illuminates and the sky near the horizon, turn red.

Probably, with a different composition of the atmosphere, for example, on other planets, the color of the sky, including at sunset, may be different. For example, the color of the sky on Mars is reddish pink.

Scattering and absorption are the main causes of the attenuation of light intensity in the atmosphere. Scattering varies as a function of the ratio of the diameter of the scattering particle to the wavelength of the light. When this ratio is less than 1/10, Rayleigh scattering occurs, in which the scattering coefficient is proportional to 1/λ 4 . For large values ​​of the ratio of the size of the scattering particles to the wavelength, the scattering law changes according to the Gustave Mie Equation; when this ratio is greater than 10, the laws of geometrical optics are applicable with sufficient accuracy for practice.

In the article you can find out a simple explanation of the blue (with shades) color of the sky. After all, the question is actually very interesting, especially for children. Let's find a simple explanation for this phenomenon, although it is not as easy to do as it seems.

The human eye can only see three colors, not as is commonly believed that the eye can see many colors. These are red, green and blue.

Introduction: why is the sky blue?

Photographic film is built exactly on the above principle. There are three surfaces in the frame, each perceives only its own light, changing color in accordance with the absorption of rays. When the light of an electric lamp passes through it, creating an image on the screen, we see millions of shades, due to their mixing in various proportions. Technology imitates nature. After all, the human eye works exactly on this principle. It contains such biological elements that react only to their own color.

And when these colors are mixed in the human brain, we observe the color that reflects the object. For example, when blue and yellow are mixed, green color. An interesting fact is that we see yellow as paler than blue or green. This is a color trick of the human eye. The black and white photo clearly shows that the yellow is not pale at all.

We see only the color that is reflected from the surface. For example, the skin of Europeans is white, while that of Africans is almost black. This only means that in some skin coloration is able to reflect all colors, which occurs when all three primary colors are mixed, while in others it can only absorb. After all, we see only reflected rays. Ideally, of course, absolutely white and absolutely black skin does not exist. But I wrote it to make it clearer.

Answer: Why is the sky blue?

“But what about the sky? - the reader, now wise by experience, will say, - is the sky capable of reflecting the rays? Agree. It passes them through, but the air surrounding the Earth, stretching for a thousand kilometers above the surface, does not pass all the rays. He partially delays red and green, and blue misses. Therefore, looking into the sky, we see it blue, blue, and in bad weather purple and even lead. The human eye, unlike various objects, practically does not reflect light, but only absorbs with its cones and rods that are sensitive to a certain color. And since the blue spectrum of rays predominates, we see it.

The sky looks blue because air scatters short wavelength light more than long wavelength light.

But this does not mean that the sky cannot be red, crimson, scarlet or pink. At least his parts. If you watch it at sunrise or sunset, you will be amazed by the riot of bloody colors. But you will not see the green, yellow sky. Why it happens? At sunrise or sunset, the sun does not penetrate the atmosphere from above, but at a very small angle, so we see a bloody dawn or a crimson sunset.

Why is the sky blue - it is very difficult to find the answer to such a simple question. Many scientists have puzzled over the answer. The best solution to the problem was proposed about 100 years ago by the English physicist Lord John Rayleigh.

But let's start from the beginning. The sun emits a dazzlingly pure white light. So the color of the sky should be the same, but it is still blue. What happens to white light in the earth's atmosphere?

A little about color

White light is a mixture of colored rays. With a prism, we can make a rainbow. The prism decomposes the white beam into colored bands: red, orange, yellow, green, blue, indigo and violet. Combining together, these rays again form white light. It can be assumed that sunlight is first split into colored components. Then something happens, and only blue rays reach the surface of the Earth.

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Hypotheses put forward at different times

There are several possible explanations. The air surrounding the Earth is a mixture of gases: nitrogen, oxygen, argon and others. The atmosphere also contains water vapor and ice crystals. Dust and other small particles are suspended in the air. The ozone layer is in the upper atmosphere. Could this be the reason?

Some scientists believed that ozone and water molecules absorb red rays and transmit blue ones. But it turned out that there was simply not enough ozone and water in the atmosphere to color the sky blue.

In 1869, Englishman John Tyndall suggested that dust and other particles scatter light. Blue light is the least scattered and passes through layers of such particles to reach the Earth's surface. In his laboratory, he created a model of smog and illuminated it with a bright white beam. The smog turned deep blue.

Tyndall decided that if the air were absolutely pure, then nothing would scatter the light, and we could admire the bright white sky. Lord Rayleigh also supported this idea, but not for long. In 1899, he published his explanation: it is air, not dust or smoke, that turns the sky blue.

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The relationship between color and wavelength - an explanation of why the sky is blue

Part sun rays passes between gas molecules without colliding with them, and reaches the surface of the Earth unchanged. The other, most part, is absorbed by gas molecules. When photons are absorbed, the molecules are excited, that is, they are charged with energy, and then emit it in the form of again photons. These secondary photons have different wavelengths and can be any color from red to purple.

They scatter in all directions: to the Earth, and to the Sun, and to the sides. Lord Rayleigh suggested that the color of the emitted beam depends on the predominance of quanta of one color or another in the beam. When a gas molecule collides with solar photons, there are eight blue quanta for one secondary red quantum.

What is the result? Intense blue light literally pours down on us from all directions from billions of atmospheric gas molecules. This light has photons of other colors mixed in, so it doesn't have a pure blue hue.

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Features of the color spectrum

Before reaching the surface of the earth, where people can contemplate it, sunlight must pass through the entire air shell planets. The light has a wide spectrum, in which the primary colors, the shades of the rainbow, still stand out. Of this spectrum, red has the longest wavelength of light, while violet has the shortest. At sunset, the solar disk rapidly turns red and rushes closer to the horizon.

In this case, the light has to overcome an increasing thickness of air, and part of the waves is lost. Purple disappears first, then blue, blue. The longest waves of red color continue to penetrate to the surface of the Earth to the last, and therefore the solar disk and the halo around it until the last moments have reddish hues.

Why is the sky blue during the day?

Long light waves can penetrate deep into the atmosphere for the reason that they are almost not absorbed, not scattered by aerosols and suspensions that constantly circulate in the planet's atmosphere. When the luminary is closer to the zenith, a different situation develops, which provides the sky with blueness. Blue has shorter wavelengths than red and is absorbed more strongly. But its dispersal ability is 4 times higher compared to red.

It is known that the sky is blue- this is the reason for the interaction of the ozone layer and sunlight. But what exactly is happening in terms of physics and why is the sky blue? There were several theories about this. All of them, in the end, confirm that the main reason is the atmosphere. But the mechanism of interaction is also explained.

Next theory assumed that the luminous flux white color passes through the atmosphere, which is made up of particles. When a light beam passes through their field, the particles are excited. Activated particles begin to emit additional rays. This is what turns the sun into a bluish color. White light, in addition to mechanical scattering and its dispersion, also activates atmospheric particles. The phenomenon resembles luminescence. On the this moment this explanation is .

The latest theory the simplest and it is sufficient to explain the main cause of the phenomenon. Its meaning is very similar to previous theories. Air is able to scatter light across the spectra. This is the main reason for the blue glow. Short wavelength light scatters more intensely than short wavelength light. Those. violet diffuses more strongly than red. This fact explains the change in the color of the sky at sunset. It is enough to change the angle of the sun. This is what happens when the earth rotates, and the color of the sky changes to orange-pink at sunset. The higher the sun is above the horizon, the more blue light we will see. The reason for everything is the same dispersion or the phenomenon of decomposition of light into spectra.

In addition to all this, you need to understand that it is impossible to exclude all the factors indicated above. After all, each of them gives some contribution to the overall picture. For example, several years ago in Moscow, as a result of abundant flowering of plants in the spring, a dense cloud of pollen formed. It turned the sky green. This is a rather rare phenomenon, but it shows that the rejected theory about microparticles in the air is also the place to be. However, this theory is not exhaustive.