The relevance of my topic lies in the fact that it will be interesting and useful for listeners because many people look at the clear blue sky, admire it, and few know why it is so blue, what gives it such a color.

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Preview:

1. Introduction. With. 3
2. Main part. With. 4 -6

1. My classmates' guesses

1. Conjectures of ancient scientists
2. Modern point of view
3. Different colors of the sky
4. Conclusion.

1. Conclusion. With. 7
2. Literature. With. 8

1. Introduction.

I like it when the weather is clear, sunny, the sky is without a single cloud, and the color of the sky is blue. “I wonder,” I thought, “why is the sky blue?”

Research topic:Why the sky is blue?

Purpose of the study:find out why the sky is blue?

Research objectives:

Find out the assumptions of ancient scientists.

Find out the modern scientific point vision.

Observe the color of the sky.

Object of study- popular science literature.

Subject of study- blue color of the sky.

Research hypotheses:

Let's say clouds consist of water vapor, and water blue color;

Or the sun has rays that paint the sky this color.

Study plan:

1. View encyclopedias;
2. Find information on the Internet;
3. Remember the topics studied about the world around you;
4. Ask mom;
5. Find out the opinions of classmates.

The relevance of my topic lies in the fact that it will be interesting and useful for listeners because many people look at the clear blue sky and admire it, and few know why it is so blue, what gives it such a color.

2. Main part.

My classmates' guesses.

I wondered what my classmates would answer to the question: why is the sky blue? Maybe someone's opinion will coincide with mine, or maybe it will be completely different.

24 students of the 3rd grade of our school were surveyed. Analysis of the responses showed:

8 students suggested that the sky is blue because of the water that evaporates from the Earth;

4 students answered that the color blue is calming;

4 students think that the color of the sky is influenced by the atmosphere and the sun;

3 students believe that space is dark and the atmosphere is white, resulting in the color blue.

2 students believe that a ray of sun is refracted in the atmosphere and the blue color is formed.

2 students suggested this option - the blue color of the sky - because it is cold.

1 student - this is how nature works.

It’s interesting that one of my hypotheses coincides with the most common opinion of the guys - clouds consist of water vapor, and water is blue.

Conjectures of ancient scientists.

When I started looking for an answer to my question in the literature, I learned that many scientists were racking their brains in search of an answer. A lot of hypotheses and assumptions were made.

For example, ancient Greek, to the question - why is the sky blue? - I would answer immediately without hesitation: “The sky is blue because it is made of the purest rock crystal!” The sky is several crystal spheres, inserted into one another with amazing accuracy. And in the middle is the Earth, with seas, cities, temples, mountain peaks, forest roads, taverns and fortresses.

This was the theory of the ancient Greeks, but why did they think so? The sky could not be touched, one could only look at it. Watch and reflect. And make various guesses. In our time, such guesses would be called “ scientific theory“, but in the era of the ancient Greeks they were called guesses. And so, after long observations and even longer reflections, the ancient Greeks decided that this was a simple and nice explanation such a strange phenomenon as the blue color of the sky.

I decided to check why they thought that way. If we put a piece of ordinary glass, we will see that it is transparent. But if you stack a whole stack of such glasses and try to look through them, you will see a bluish tint.

This simple explanation of the color of the sky lasted for one and a half thousand years.

Leonardo da Vinci suggested that the sky is painted this color because “...light over darkness becomes blue...”.

Some other scientists had the same opinion, but still, later it became clear that this hypothesis is fundamentally incorrect, because if you mix black with white, you are unlikely to get blue, because the combination of these colors gives only gray and its shades.

A little later in the 18th century, it was believed that the color of the sky was given by the components of the air. According to this theory, it was believed that air contains many impurities, since fresh air would be black. After this theory, there were many more assumptions and conjectures, but not one of them could justify itself.

Modern point of view.

I turned to the opinion of modern scientists. Modern scientists have found the answer and proven why the sky is blue.

The sky is just air, that ordinary air that we breathe every second, that which cannot be seen or touched, because it is transparent and weightless. But we breathe transparent air, why does it become such a blue color above our heads?

The whole secret turned out to be in our atmosphere.

The sun's rays must pass through a huge layer of air before hitting the ground.

The sun's ray is white. A White color is a mixture of colored rays. Like the little rhyme that makes it easy to remember the colors of the rainbow:

1. each (red)
2. hunter (orange)
3. wishes (yellow)
4. know (green)
5. where (blue)
6. sitting (blue)
7. pheasant (purple)

A ray of sun, colliding with air particles, breaks up into rays of seven colors.

Red and orange rays are the longest and pass from the sun directly into our eyes. And blue rays are the shortest, bounce off air particles in all directions and reach the ground less than all others. Thus, the sky is permeated with blue rays.

Different colors of the sky.

The sky is not always blue. For example, at night, when the sun does not send rays, we see the sky not blue, the atmosphere seems transparent. And through the transparent air, a person can see planets and stars. And during the day, the blue color again hides cosmic bodies from our eyes.

The color of the sky can be red - at sunset, in cloudy weather, white or gray.

Conclusions.

So after doing my research I can do the following conclusions:

1. the whole secret is in the color of the sky in our atmosphere- in the air shell of planet Earth.
2. A ray of sun passing through the atmosphere breaks up into rays of seven colors.
3. Red and orange rays are the longest, and blue rays are the shortest..
4. Blue rays reach the Earth less than others, and thanks to these rays the sky is permeated with blue.
5. The sky is not always blue.

The main thing is that now I know why the sky is blue. My second hypothesis was partially confirmed; the sun has rays that paint the sky this color. The guesses of my two classmates turned out to be the closest to the correct answer.

Simple explanation

What is heaven?

The sky is infinity. For any nation, the sky is a symbol of purity, because it is believed that God himself lives there. People, turning to the sky, ask for rain, or vice versa for the sun. That is, the sky is not just air, the sky is a symbol of purity and innocence.

Sky - it is just air, that ordinary air that we breathe every second, that cannot be seen or touched, because it is transparent and weightless. But we breathe transparent air, why does it become such a blue color above our heads? Air contains several elements, nitrogen, oxygen, carbon dioxide, water vapor, various specks of dust that are constantly in motion.

From a physics point of view

In practice, as physicists say, the sky is just air colored by the sun's rays. To put it simply, the sun shines on the Earth, but Sun rays To do this, they must pass through a huge layer of air that literally envelops the Earth. And just like a ray of sunshine has many colors, or rather seven colors of the rainbow. For those who do not know, it is worth recalling that the seven colors of the rainbow are red, orange, yellow, green, blue, indigo, violet.

Moreover, each ray has all these colors and, when passing through this layer of air, it sprays various colors of the rainbow in all directions, but the strongest scattering of the blue color occurs, due to which the sky acquires a blue color. To describe it briefly, the blue sky is the splashes produced by a beam colored in this color.

And on the moon

There is no atmosphere and therefore the sky on the Moon is not blue, but black. Astronauts who go into orbit see a black, black sky on which planets and stars sparkle. Of course, the sky on the Moon looks very beautiful, but you still wouldn’t want to see a constantly black sky above your head.

The sky changes color

The sky is not always blue; it tends to change color. Everyone has probably noticed that sometimes it is whitish, sometimes blue-black... Why is that? For example, at night, when the sun does not send its rays, we see the sky not blue, the atmosphere seems transparent to us. And through the transparent air, a person can see planets and stars. And during the day, the blue color will again reliably hide the mysterious space from prying eyes.

Various hypotheses Why is the sky blue? (hypotheses of Goethe, Newton, 18th century scientists, Rayleigh)

What hypotheses have not been put forward in different time to explain the color of the sky. Observing how the smoke against the background of a dark fireplace acquires a bluish color, Leonardo da Vinci wrote: “... light over darkness becomes blue, the more beautiful, the more excellent the light and dark are.” He adhered to approximately the same point of view Goethe, who was not only a world-famous poet, but also the greatest natural scientist of his time. However, this explanation of the color of the sky turned out to be untenable, since, as it became obvious later, mixing black and white can only produce gray tones, not colored ones. The blue color of smoke from a fireplace is caused by a completely different process.

Following the discovery of interference, particularly in thin films, Newton tried to apply interference to explain the color of the sky. To do this, he had to assume that water droplets have the shape of thin-walled bubbles, like soap bubbles. But since the droplets of water contained in the atmosphere are actually spheres, this hypothesis soon “burst” like a soap bubble.

Scientists of the 18th century Marriott, Bouguer, Euler thought that the blue color of the sky was explained by its own color components air. This explanation even received some confirmation later, already in the 19th century, when it was established that liquid oxygen is blue, and liquid ozone is blue. Closest to correct explanation the color of the sky approached O.B. Saussure. He believed that if the air were absolutely pure, the sky would be black, but the air contains impurities that reflect predominantly blue color (in particular, water vapor and water droplets). By the second half of the 19th century. Rich experimental material has accumulated on the scattering of light in liquids and gases; in particular, one of the characteristics of scattered light coming from the sky—its polarization—was discovered. Arago was the first to discover and explore it. This was in 1809. Later, Babinet, Brewster and other scientists studied the polarization of the sky. The question of the color of the sky attracted the attention of scientists so much that experiments on the scattering of light in liquids and gases, which had a much broader significance, were carried out from the angle of view of “laboratory reproduction of the blue color of the sky.” The titles of the works indicate this: “Modeling the blue color of the sky "Brücke or "On the Blue Color of the Sky, the Polarization of Light by Cloudy Matter in General" by Tyndall The successes of these experiments directed the thoughts of scientists. the right way- look for the reason for the blue color of the sky in the scattering of sunlight in the atmosphere.

The first to create a harmonious, rigorous mathematical theory molecular scattering light in the atmosphere, was the English scientist Rayleigh. He believed that light scattering occurs not on impurities, as his predecessors thought, but on the air molecules themselves. Rayleigh's first work on light scattering was published in 1871. In its final form, his theory of scattering, based on electromagnetic nature light, established by that time, was set out in the work “On Light from the Sky, Its Polarization and Color,” published in 1899. For work in the field of light scattering, Rayleigh (his full name John William Strett, Lord Rayleigh III) is often called Rayleigh the Scatterer, in contrast to his son, Lord Rayleigh IV. Rayleigh IV is called Atmospheric Rayleigh for his great contribution to the development of atmospheric physics. To explain the color of the sky, we will present only one of the conclusions of Rayleigh’s theory; we will refer to others several times in explaining various optical phenomena. This conclusion states that the brightness, or intensity, of scattered light varies inversely with the fourth power of the wavelength of the light incident on the scattering particle. Thus, molecular scattering is extremely sensitive to the slightest change in the wavelength of light. For example, the wavelength of violet rays (0.4 μm) is approximately half the wavelength of red rays (0.8 μm). Therefore, violet rays will be scattered 16 times more strongly than red ones, and with equal intensity of incident rays there will be 16 times more of them in the scattered light. All other colored rays of the visible spectrum (blue, cyan, green, yellow, orange) will be included in the scattered light in quantities inversely proportional to the fourth power of the wavelength of each of them. If now all the colored scattered rays are mixed in this ratio, then the color of the mixture of scattered rays will be blue.

Direct sunlight (i.e. light emanating directly from the solar disk), losing mainly blue and violet rays due to scattering, acquires a weak yellowish tint, which intensifies as the Sun descends to the horizon. Now the rays have to travel a longer and longer path through the atmosphere. Over a long path, the loss of short-wave, i.e., violet, blue, cyan, rays becomes more and more noticeable, and in direct light Mostly long-wave rays - red, orange, yellow - reach the surface of the Earth. Therefore, the color of the Sun and Moon first becomes yellow, then orange and red. The red color of the Sun and the blue color of the sky are two consequences of the same scattering process. In direct light, after it passes through the atmosphere, predominantly long-wave rays remain (red Sun), while diffuse light contains short-wave rays (blue sky). Thus, Rayleigh’s theory very clearly and convincingly explained the mystery of the blue sky and the red Sun.

sky thermal molecular scattering

When the wind throws a white fluffy transparent cape over the beautiful blue sky, people begin to look up more and more often. If at the same time it also puts on a large gray fur coat with silver threads of rain, then those around it hide from it under umbrellas. If the outfit is dark purple, then everyone is sitting at home and wants to see the sunny blue sky.

And only when the long-awaited sunny blue sky appears, which puts on a dazzling blue dress decorated with golden rays of the sun, people rejoice - and, smiling, leave their houses in anticipation of good weather.

The question of why the sky is blue has worried human minds since time immemorial. Greek legends have found their answer. They claimed that this shade was given to it by the purest rock crystal.

During the time of Leonardo da Vinci and Goethe, they also sought an answer to the question of why the sky is blue. They believed that the blue color of the sky is obtained by mixing light with darkness. But later this theory was refuted as untenable, since it turned out that by combining these colors, you can only get tones of the gray spectrum, but not color.

After some time, the answer to the question of why the sky is blue was attempted to be explained in the 18th century by Marriott, Bouguer and Euler. They believed that this was the natural color of the particles that made up the air. This theory was popular even at the beginning of the next century, especially when it was found that liquid oxygen is blue and liquid ozone is blue.

Saussure was the first to come up with a more or less sensible idea, who suggested that if the air were completely pure, without impurities, the sky would turn out to be black. But since the atmosphere contains various elements(for example, steam or water drops), then they, reflecting the color, give the sky the desired shade.

After this, scientists began to get closer and closer to the truth. Arago discovered polarization, one of the characteristics of scattered light that bounces off the sky. Physics definitely helped the scientist in this discovery. Later, other researchers began to look for the answer. At the same time, the question of why the sky is blue interested scientists so much that to find out it was carried out great amount various experiments that led to the idea that main reason The appearance of blue color is due to the fact that the rays of our Sun are simply scattered in the atmosphere.

Explanation

The first to create a mathematically based answer for molecular light scattering was the British researcher Rayleigh. He hypothesized that light is scattered not because of impurities in the atmosphere, but because of the air molecules themselves. His theory was developed - and this is the conclusion the scientists came to.

The sun's rays make their way to the Earth through its atmosphere (a thick layer of air), the so-called air envelope planets. The dark sky is completely filled with air, which, despite being completely transparent, is not empty, but consists of gas molecules - nitrogen (78%) and oxygen (21%), as well as water droplets, steam, ice crystals and small pieces hard material(for example, particles of dust, soot, ash, ocean salt, etc.).

Some rays manage to pass freely between gas molecules, completely bypassing them, and therefore reach the surface of our planet without changes, but most of the rays collide with gas molecules, which become excited, receive energy and are released into different sides multi-colored rays, completely coloring the sky, resulting in us seeing a sunny blue sky.

White light itself consists of all the colors of the rainbow, which can often be seen when it is broken down into its component parts. It so happens that air molecules scatter blue and violet colors the most, since they are the most short part spectrum because they have the shortest wavelength.

When mixed in an atmosphere of blue and purple flowers With a small amount red, yellow and green, the sky begins to “glow” blue.

Since the atmosphere of our planet is not homogeneous, but rather different (near the surface of the Earth it is denser than above), it has different structure and properties, we can observe blue tints. Before sunset or sunrise, when the length of the sun's rays increases significantly, blue and violet colors are scattered in the atmosphere and absolutely do not reach the surface of our planet. The yellow-red waves, which we observe in the sky during this period of time, successfully reach.

At night, when the sun's rays cannot reach a certain side of the planet, the atmosphere there becomes transparent, and we see “black” space. This is exactly how astronauts above the atmosphere see it. It is worth noting that the astronauts were lucky, because when they are more than 15 km above the surface of the earth, during the day they can simultaneously observe the Sun and the stars.

Color of the sky on other planets

Since the color of the sky largely depends on the atmosphere, it is not surprising that different planets it different colors. It’s interesting that Saturn’s atmosphere is the same color as our planet’s.

The sky of Uranus is a very beautiful aquamarine color. Its atmosphere consists mainly of helium and hydrogen. It also contains methane, which completely absorbs red and scatters green and blue colors. Neptune's skies are blue: in the atmosphere of this planet there is not as much helium and hydrogen as ours, but there is a lot of methane, which neutralizes red light.

The atmosphere on the Moon, the Earth's satellite, as well as on Mercury and Pluto, is completely absent, therefore, light rays are not reflected, so the sky here is black, and the stars are easily distinguishable. Blue and green colors The sun's rays are completely absorbed by the atmosphere of Venus, and when the Sun is near the horizon, the skies are yellow.

Why the sky is blue? It is difficult to find an answer to such a simple question. Many scientists racked their brains in search of an answer. The best solution the problem was proposed about 100 years ago by an English physicist Lord John Rayleigh.

The sun emits dazzlingly pure white light. This means the color of the sky should be the same, but it is still blue. What happens to white light in the earth's atmosphere?

White light is a mixture of colored rays. Using a prism we can make a rainbow.

The prism splits the white beam into colored stripes:

■Red

■Orange

■ Yellow

■ Green

■ Blue

■ Blue

■ Purple

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.

So why is the sky blue?

There are several possible explanations. The air surrounding the Earth is a mixture of gases: nitrogen, oxygen, argon and others. There is also water vapor and ice crystals in the atmosphere. Dust and other small particles are suspended in the air. IN upper layers There is a layer of ozone in the 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, an Englishman John Tindall suggested that dust and other particles scatter light. Blue light is scattered the least 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 a deep blue. Tindall decided that if the air were absolutely clear, 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 colors the sky blue.

The main theory about the blue color of the sky

Some of the sun's rays pass between gas molecules without colliding with them and reach the Earth's surface unchanged. Another, most of, is absorbed by gas molecules. When photons are absorbed, molecules become excited, that is, they are charged with energy, and then emit it in the form of photons. These secondary photons have different wavelengths and can be any color from red to violet. They fly away in all directions: towards the Earth, towards 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 photons of solar rays, 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 gas molecules in the atmosphere. This light has photons of other colors mixed in, so it is not purely blue.

Why then is the sunset red?

However, the sky is not always blue. The question naturally arises: if we see blue skies all day, why is the sunset red? Red color is the least scattered by gas molecules. During sunset, the Sun approaches the horizon and the sun's ray is directed towards the Earth's surface not vertically, as during the day, but at an angle.

Therefore, the path it takes through the atmosphere is much Furthermore that it takes place during the day when the Sun is high. Because of this, the blue-blue spectrum is absorbed in a thick layer of the atmosphere, not reaching the Earth. And the longer ones light waves of the red-yellow spectrum reach the surface of the Earth, coloring the sky and clouds in the red and yellow colors characteristic of sunset.

Scientific explanation

Above we gave the answer in relatively simple language. Below we quote the rationale using scientific terms and formulas.

Excerpt from Wiki:

The reason the sky appears blue is because air scatters short-wavelength light more than long-wavelength light. The intensity of Rayleigh scattering, caused by fluctuations in the number of molecules of air gases in volumes commensurate with the wavelengths of light, is proportional to 1/λ 4, λ is the wavelength, i.e. the violet portion of the visible spectrum is scattered approximately 16 times more intensely than the red. Because blue light has a shorter wavelength, at the end of the visible spectrum, it is scattered more into the atmosphere than red light. Due to this, the area 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 violet color in it is less, and also due to the less sensitivity of the eye to purple color and more to blue, which irritates not only the blue-sensitive cones in the retina, but also those sensitive to red and green rays).

During sunset and dawn, light passes tangentially to earth's surface, so 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 and sky illuminated by it and the sky near the horizon, are painted in red tones.

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 reasons for the weakening 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 . At larger 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 geometric optics are applied with sufficient accuracy for practice.

The joy of seeing and understanding
is the most beautiful gift of nature.
Albert Einstein

The mystery of the sky blue

Why the sky is blue?...

There is no person who has not thought about this at least once in his life. Medieval thinkers already tried to explain the origin of the color of the sky. Some of them suggested that blue was the true color of air or one of its constituent gases. Others thought that the true color of the sky was black - the way it looks at night. During the day, the black color of the sky is combined with the white color of the sun’s rays, and the result is... blue.

Now, perhaps, you will not meet a person who, wanting to get blue paint, would mix black and white. And there was a time when the laws of color mixing were still unclear. They were installed just three hundred years ago by Newton.

Newton became interested in the mystery sky blue. He began by rejecting all previous theories.

First, he argued, a mixture of white and black never produces blue. Secondly, blue is not the true color of air at all. If this were so, then the Sun and Moon at sunset would not appear red, as they really are, but blue. This is what the peaks of distant snowy mountains would look like.

Imagine the air is colored. Even if it is very weak. Then a thick layer of it would act like painted glass. And if you look through painted glass, then all objects will seem to be the same color as this glass. Why do distant snowy peaks appear to us pink, and not blue at all?

In the dispute with his predecessors, the truth was on Newton's side. He proved that the air is not colored.

But still he did not solve the riddle of the heavenly azure. He was confused by the rainbow, one of the most beautiful, poetic phenomena of nature. Why does it suddenly appear and disappear just as unexpectedly? Newton could not be satisfied with the prevailing superstition: a rainbow is a sign from above, it foretells good weather. He sought to find the material cause of every phenomenon. He also found the reason for the rainbow.

Rainbows are the result of light refraction in raindrops. Having understood this, Newton was able to calculate the shape of the rainbow arc and explain the sequence of colors of the rainbow. His theory could not explain only the appearance of a double rainbow, but this was done only three centuries later with the help of a very complex theory.

The success of the rainbow theory hypnotized Newton. He mistakenly decided that the blue color of the sky and the rainbow were caused by the same reason. A rainbow really breaks out when the rays of the Sun break through a swarm of raindrops. But the blueness of the sky is visible not only in the rain! On the contrary, it is in clear weather, when there is not even a hint of rain, that the sky is especially blue. How did the great scientist not notice this? Newton thought that tiny bubbles of water, which according to his theory formed only the blue part of the rainbow, floated in the air in any weather. But this was a delusion.

First solution

Almost 200 years passed, and another English scientist took up this issue - Rayleigh, who was not afraid that the task was beyond the power of even the great Newton.

Rayleigh studied optics. And people who devote their lives to the study of light spend a lot of time in the dark. Extraneous light interferes with the finest experiments, which is why the windows of the optical laboratory are almost always covered with black, impenetrable curtains.

Rayleigh remained for hours in his gloomy laboratory alone with beams of light escaping from the instruments. In the path of the rays they swirled like living specks of dust. They were brightly lit and therefore stood out against the dark background. The scientist may have spent a long time thoughtfully watching their smooth movements, just as a person watches the play of sparks in a fireplace.

Were it not these specks of dust dancing in the rays of light that suggested to Rayleigh new thought about the origin of the color of the sky?

Even in ancient times, it became known that light travels in a straight line. This important discovery could have been made by primitive man, observing how, breaking through the cracks of the hut, the sun's rays fell on the walls and floor.

But it’s unlikely that he was bothered by the thought of why he sees light rays when looking at them from the side. And here there is something to think about. After all, sunlight beams from the crack to the floor. The observer's eye is located to the side and, nevertheless, sees this light.

We also see light from a spotlight aimed at the sky. This means that part of the light is somehow deviated from the direct path and directed into our eye.

What makes him go astray? It turns out that these are the very specks of dust that fill the air. Rays that are scattered by a speck of dust and rays enter our eye, which, encountering obstacles, turn off the road and spread in a straight line from the scattering speck of dust to our eye.

“Is it these specks of dust that color the sky blue?” – Rayleigh thought one day. He did the math and the guess turned into a certainty. He found an explanation for the blue color of the sky, red dawns and blue haze! Well, of course, tiny grains of dust, the size of which is smaller than the wavelength of light, scatter sunlight and the shorter its wavelength, the more strongly, Rayleigh announced in 1871. And since violet and blue rays in the visible solar spectrum have the shortest wavelength, they are scattered most strongly, giving the sky a blue color.

The Sun and snowy peaks obeyed this calculation of Rayleigh. They even confirmed the scientist's theory. At sunrise and sunset, when sunlight passes through the greatest thickness of air, violet and blue rays, says Rayleigh's theory, are scattered most strongly. At the same time, they deviate from the straight path and do not catch the eye of the observer. The observer sees mainly red rays, which are scattered much more weakly. That's why the sun appears red to us at sunrise and sunset. For the same reason, the peaks of distant snowy mountains appear pink.

Looking at the clear sky, we see blue-blue rays that deviate from the straight path due to scattering and fall into our eyes. And the haze that we sometimes see near the horizon also seems blue to us.

Annoying trifle

Isn't it a beautiful explanation? Rayleigh himself was so carried away by it, scientists were so amazed by the harmony of the theory and Rayleigh’s victory over Newton that none of them noticed one simple thing. This trifle, however, should have completely changed their assessment.

Who will deny that far from the city, where there is much less dust in the air, the blue color of the sky is especially clear and bright? It was difficult for Rayleigh himself to deny this. Therefore... it's not dust particles that scatter light? Then what?

He reviewed all his calculations again and became convinced that his equations were correct, but this meant that the scattering particles were indeed not dust grains. In addition, the dust grains that are present in the air are much longer than the wavelength of light, and calculations convinced Rayleigh that a large accumulation of them does not enhance the blueness of the sky, but, on the contrary, weakens it. The scattering of light by large particles weakly depends on the wavelength and therefore does not cause a change in its color.

When light is scattered on large particles, both the scattered and transmitted light remains white, therefore the appearance of large particles in the air gives the sky a whitish color, and the accumulation large quantity Large droplets cause the white color of clouds and fog. This is easy to check on an ordinary cigarette. The smoke coming out of it from the mouthpiece always appears whitish, and the smoke rising from its burning end is bluish in color.

The smallest particles of smoke rising from the burning end of a cigarette are smaller than the wavelength of light and, according to Rayleigh's theory, scatter predominantly violet and blue colors. But when passing through narrow channels in the thickness of tobacco, smoke particles stick together (coagulate), uniting into larger lumps. Many of them become larger than the wavelengths of light, and they scatter all wavelengths of light approximately equally. This is why the smoke coming from the mouthpiece appears whitish.

Yes, it was useless to argue and defend a theory based on specks of dust.

So, the mystery of the blue color of the sky again arose before scientists. But Rayleigh did not give up. If the blue color of the sky is the purer and brighter the purer the atmosphere, he reasoned, then the color of the sky cannot be caused by anything other than the molecules of the air itself. Air molecules, he wrote in his new articles, are the smallest particles that scatter the light of the sun!

This time Rayleigh was very careful. Before reporting his new idea, he decided to test it, to somehow compare the theory with experience.

The opportunity presented itself in 1906. Rayleigh was helped by the American astrophysicist Abbott, who studied the blue glow of the sky at the Mount Wilson Observatory. By processing the results of measuring the brightness of the sky based on Rayleigh scattering theory, Abbott calculated the number of molecules contained in each cubic centimeter of air. It turned out to be a huge number! Suffice it to say that if these molecules were distributed to all the people inhabiting Earth, then everyone will get more than 10 billion of these molecules. In short, Abbott discovered that in every cubic centimeter of air at normal temperature and atmospheric pressure contains 27 billion times a billion molecules.

The number of molecules in a cubic centimeter of gas can be determined different ways based on completely different and independent phenomena. They all lead to closely matching results and give a number called the Loschmidt number.

This number is well known to scientists, and more than once it has served as a measure and control in explaining phenomena occurring in gases.

And so the number obtained by Abbott when measuring the glow of the sky coincided with Loschmidt’s number with great accuracy. But in his calculations he used the Rayleigh scattering theory. Thus, this clearly proved that the theory was correct, molecular scattering of light really exists.

It seemed that Rayleigh's theory was reliably confirmed by experience; all scientists considered it flawless.

It became generally accepted and was included in all optics textbooks. One could breathe easy: finally an explanation had been found for a phenomenon that was so familiar and yet mysterious.

It is all the more surprising that in 1907, on the pages of the famous scientific journal the question was again raised: why is the sky blue?!.

Dispute

Who dared to question the generally accepted Rayleigh theory?

Oddly enough, this was one of Rayleigh's most ardent admirers and admirers. Perhaps no one appreciated and understood Rayleigh so much, knew his works so well, and was not as interested in his scientific work as the young Russian physicist Leonid Mandelstam.

“The character of Leonid Isaakovich’s mind,” another Soviet scientist, Academician N.D. later recalled. Papaleksi - had a lot in common with Rayleigh. And it is no coincidence that their ways scientific creativity often walked in parallel and crossed over repeatedly.

They crossed themselves this time, too, on the question of the origin of the color of the sky. Before this, Mandelstam was mainly interested in radio engineering. For the beginning of our century it was absolutely new area science, and few people understood it. After the discovery of A.S. Popov (in 1895) only a few years had passed, and there was no end to the work to be done. In a short period, Mandelstam carried out a lot of serious research in the field electromagnetic vibrations in relation to radio engineering devices. In 1902 he defended his dissertation and at the age of twenty-three received the degree of Doctor of Natural Philosophy from the University of Strasbourg.

While dealing with the issues of excitation of radio waves, Mandelstam naturally studied the works of Rayleigh, who was a recognized authority in the study oscillatory processes. And the young doctor inevitably became acquainted with the problem of coloring the sky.

But, having become acquainted with the issue of the color of the sky, Mandelstam not only showed the fallacy, or, as he himself said, the “inadequacy” of the generally accepted theory of molecular light scattering of Rayleigh, not only revealed the secret of the blue color of the sky, but also laid the foundation for research that led to one of the most important discoveries physics of the XX century.

It all started with a dispute in absentia with one of the greatest physicists, the father of quantum theory, M. Planck. When Mandelstam became acquainted with Rayleigh's theory, it captivated him with its reticence and internal paradoxes, which, to the surprise of the young physicist, the old, experienced Rayleigh did not notice. The insufficiency of Rayleigh's theory was especially clearly revealed when analyzing another theory, built on its basis by Planck to explain the attenuation of light when passing through an optically homogeneous transparent medium.

In this theory, it was taken as a basis that the very molecules of the substance through which light passes are sources of secondary waves. To create these secondary waves, Planck argued, part of the energy of the passing wave is spent, which is attenuated. We see that this theory is based on the Rayleigh theory of molecular scattering and relies on its authority.

The easiest way to understand the essence of the matter is by looking at the waves on the surface of the water. If a wave encounters stationary or floating objects (piles, logs, boats, etc.), then small waves scatter in all directions from these objects. This is nothing more than scattering. Part of the energy of the incident wave is spent on exciting secondary waves, which are quite similar to scattered light in optics. In this case, the initial wave is weakened - it fades.

Floating objects can be much smaller than the wavelength traveling through the water. Even small grains will cause secondary waves. Of course, as the particle size decreases, the secondary waves they form weaken, but they will still take away the energy of the main wave.

This is roughly how Planck imagined the process of weakening a light wave as it passes through a gas, but the role of grains in his theory was played by gas molecules.

Mandelstam became interested in this work of Planck.

Mandelstam's train of thought can also be explained using the example of waves on the surface of water. You just need to look at it more carefully. So, even small grains floating on the surface of the water are sources of secondary waves. But what will happen if these grains are poured so thickly that they cover the entire surface of the water? Then it will turn out that individual secondary waves caused by numerous grains will add up in such a way that they will completely extinguish those parts of the waves that run to the sides and backwards, and scattering will stop. All that remains is a wave running forward. She will run forward without weakening at all. The only result of the presence of the entire mass of grains will be a slight decrease in the speed of propagation of the primary wave. It is especially important that all this does not depend on whether the grains are stationary or moving on the surface of the water. The aggregate of grains will simply act as a load on the surface of the water, changing the density of its upper layer.

Mandelstam made a mathematical calculation for the case when the number of molecules in the air is so large that even such a small area as the wavelength of light contains very big number molecules. It turned out that in this case, secondary light waves excited by individual chaotically moving molecules add up in the same way as the waves in the example with grains. This means that in this case the light wave propagates without scattering and attenuation, but at a slightly lower speed. This refuted the theory of Rayleigh, who believed that the movement of scattering particles in all cases ensures the scattering of waves, and therefore refuted Planck’s theory based on it.

Thus, sand was discovered under the foundation of the scattering theory. The entire majestic building began to shake and threatened to collapse.

Coincidence

But what about determining the Loschmidt number from measurements of the blue glow of the sky? After all, experience confirmed the Rayleigh theory of scattering!

“This coincidence should be considered accidental,” Mandelstam wrote in 1907 in his work “On Optically Homogeneous and Turbid Media.”

Mandelstam showed that the random movement of molecules cannot make a gas homogeneous. On the contrary, in real gas There are always tiny rarefactions and compactions formed as a result of chaotic thermal movement. It is they that lead to the scattering of light, as they disrupt the optical homogeneity of the air. In the same work, Mandelstam wrote:

“If the medium is optically inhomogeneous, then, generally speaking, the incident light will also be scattered to the sides.”

But since the sizes of inhomogeneities arising as a result of chaotic motion are smaller than the length of light waves, the waves corresponding to the violet and blue parts of the spectrum will be scattered predominantly. And this leads, in particular, to the blue color of the sky.

Thus the riddle of the azure sky was finally solved. Theoretical part was developed by Rayleigh. Physical nature diffusers was installed by Mandelstam.

Mandelstam's great merit lies in the fact that he proved that the assumption of perfect homogeneity of a gas is incompatible with the fact of light scattering in it. He realized that the blue color of the sky proved that the homogeneity of gases was only apparent. More precisely, gases appear homogeneous only when examined with crude instruments, such as a barometer, scales or other instruments that are affected by many billions of molecules at once. But the light beam senses incomparably smaller quantities of molecules, measured only in tens of thousands. And this is enough to establish beyond doubt that the density of the gas is continuously subject to small local changes. Therefore, a medium that is homogeneous from our “rough” point of view is in reality heterogeneous. From the “point of view of light” it appears cloudy and therefore scatters light.

Random local changes in the properties of a substance, resulting from the thermal movement of molecules, are now called fluctuations. Having elucidated the fluctuation origin of molecular light scattering, Mandelstam paved the way for a new method of studying matter - the fluctuation, or statistical, method, which was later developed by Smoluchowski, Lorentz, Einstein and himself into a new large department of physics - statistical physics.

The sky should twinkle!

So, the mystery of the blue color of the sky was revealed. But the study of light scattering did not stop there. Drawing attention to almost imperceptible changes in air density and explaining the color of the sky by fluctuational scattering of light, Mandelstam, with his keen sense of a scientist, discovered a new, even more subtle feature of this process.

After all, air inhomogeneities are caused by random fluctuations in its density. The magnitude of these random inhomogeneities and the density of the clumps changes over time. Therefore, the scientist reasoned, the intensity—the strength of the scattered light—should also change over time! After all, the denser the clumps of molecules, the more intense the light scattered on them. And since these clumps appear and disappear chaotically, the sky, simply put, should twinkle! The strength of its glow and its color should change all the time (but very weakly)! But has anyone ever noticed such a flickering? Of course not.

This effect is so subtle that with the naked eye you won't notice it.

None of the scientists have observed such a change in the sky glow either. Mandelstam himself did not have the opportunity to verify the conclusions of his theory. The organization of complex experiments was initially hampered by poor conditions Tsarist Russia, and then the difficulties of the first years of the revolution, foreign intervention and civil war.

In 1925, Mandelstam became head of the department at Moscow University. Here he met with the outstanding scientist and skilled experimenter Grigory Samuilovich Landsberg. And so, connected by deep friendship and common scientific interests, together they continued their assault on the secrets hidden in the faint rays of scattered light.

The optical laboratories of the university in those years were still very poor in instruments. There was not a single instrument at the university capable of detecting the flickering of the sky or those small differences in the frequencies of incident and scattered light that theory predicted were the result of this flickering.

However, this did not stop the researchers. They gave up the idea of ​​imitating the sky in laboratory conditions. This would only complicate an already subtle experience. They decided to study not the scattering of white - complex light, but the scattering of rays of one, strictly defined frequency. If they know exactly the frequency of the incident light, it will be much easier to look for those frequencies close to it that should arise during scattering. In addition, the theory suggested that observations were easier to make in solids, since in them the molecules are located much more closely than in gases, and the more dense the substance, the greater the scattering.

A painstaking search began for the most suitable materials. Finally the choice fell on quartz crystals. Just because they're big clear crystals quartz is more accessible than any other.

It lasted two years preparatory experiments, the purest samples of crystals were selected, the technique was improved, signs were established by which it was possible to indisputably distinguish scattering on quartz molecules from scattering on random inclusions, crystal inhomogeneities and impurities.

Wit and work

Lacking powerful equipment for spectral analysis, scientists chose an ingenious workaround that was supposed to make it possible to use existing instruments.

The main difficulty in this work was that the weak light caused by molecular scattering was superimposed by much stronger light scattered by small impurities and other defects in the crystal samples that were obtained for the experiments. The researchers decided to take advantage of the fact that scattered light formed by crystal defects and reflections from various parts settings exactly matches the frequency of the incident light. They were only interested in light with a frequency changed in accordance with Mandelstam's theory. Thus, the task was to highlight the light of a changed frequency caused by molecular scattering against the background of this much brighter light.

To ensure that the scattered light had a magnitude that could be detected, the scientists decided to illuminate the quartz with the most powerful lighting device available to them: a mercury lamp.

So, the light scattered in the crystal must consist of two parts: weak light altered frequency, due to molecular scattering (the study of this part was the goal of scientists), and from much stronger light of unaltered frequency, caused due to extraneous reasons(this part was harmful, it made the research difficult).

The idea of ​​the method was attractive due to its simplicity: it is necessary to absorb light of a constant frequency and pass only light of a changed frequency into the spectral apparatus. But the frequency differences were only a few thousandths of a percent. No laboratory in the world had a filter capable of separating such close frequencies. However, a solution was found.

Scattered light was passed through a vessel containing mercury vapor. As a result, all the “harmful” light was “stuck” in the vessel, and the “useful” light passed through without noticeable attenuation. The experimenters took advantage of one already known circumstance. An atom of matter, as quantum physics claims, is capable of emitting light waves only at very specific frequencies. At the same time, this atom is also capable of absorbing light. Moreover, only light waves of those frequencies that he himself can emit.

In a mercury lamp, light is emitted by mercury vapor, which glows under the influence electrical discharge, occurring inside the lamp. If this light is passed through a vessel also containing mercury vapor, it will be almost completely absorbed. What the theory predicts will happen: the mercury atoms in the vessel will absorb the light emitted by the mercury atoms in the lamp.

Light from other sources, such as a neon lamp, will pass through mercury vapor unharmed. The mercury atoms will not even pay attention to it. That part of the light from a mercury lamp that was scattered in quartz with a change in wavelength will not be absorbed either.

It was this convenient circumstance that Mandelstam and Landsberg took advantage of.

Amazing discovery

In 1927, decisive experiments began. Scientists illuminated a quartz crystal with the light of a mercury lamp and processed the results. And... they were surprised.

The results of the experiment were unexpected and unusual. What scientists discovered was not at all what they expected, not what was predicted by theory. They discovered a completely new phenomenon. But which one? And isn't this a mistake? The scattered light did not reveal the expected frequencies, but much higher and lower frequencies. A whole combination of frequencies appeared in the spectrum of scattered light that were not present in the light incident on the quartz. It was simply impossible to explain their appearance by optical inhomogeneities in quartz.

A thorough check began. The experiments were carried out flawlessly. They were conceived so witty, perfect and inventive that one could not help but admire them.

“Leonid Isaakovich sometimes solved very difficult technical problems so beautifully and sometimes brilliantly simply that each of us involuntarily asked the question: “Why didn’t this occur to me before?” - says one of the employees.

Various control experiments persistently confirmed that there was no error. In photographs of the spectrum of scattered light, weak and yet quite obvious lines persistently appeared, indicating the presence of “extra” frequencies in the scattered light.

For many months, scientists have been looking for an explanation for this phenomenon. Where did “alien” frequencies appear in the scattered light?!

And the day came when Mandelstam was struck by an amazing guess. It was an amazing discovery, the same one that is now considered one of the most important discoveries of the 20th century.

But both Mandelstam and Landsberg came to a unanimous decision that this discovery could be published only after a solid check, after an exhaustive penetration into the depths of the phenomenon. The final experiments have begun.

With the help of the sun

On February 16, Indian scientists C.N. Raman and K.S. Krishnan sent a telegram from Calcutta to this magazine with short description of his discovery.

In those years, letters about a variety of discoveries flocked to the Nature magazine from all over the world. But not every message is destined to cause excitement among scientists. When the issue with the letter from Indian scientists came out, the physicists were very excited. The title of the note alone is “ New type secondary radiation” – aroused interest. After all, optics is one of the oldest sciences; it was not often possible to discover something unknown in it in the 20th century.

One can imagine with what interest physicists around the world awaited new letters from Calcutta.

Their interest was fueled to a large extent by the very personality of one of the authors of the discovery, Raman. This is a man of a curious fate and an extraordinary biography, very similar to Einstein’s. Einstein in his youth was a simple gymnasium teacher, and then an employee of the patent office. It was during this period that he completed the most significant of his works. Raman, a brilliant physicist, also after graduating from university, was forced to serve in the finance department for ten years and only after that was invited to the department of Calcutta University. Raman soon became the recognized head of the Indian school of physicists.

Shortly before the events described, Raman and Krishnan became interested in a curious task. At that time, the passions caused by the discovery in 1923 had not yet subsided American physicist Compton, who, while studying the passage of X-rays through matter, discovered that some of these rays, scattering away from the original direction, increase their wavelength. Translated into the language of optics, we can say that X-rays, colliding with the molecules of a substance, changed their “color”.

This phenomenon was easily explained by the laws of quantum physics. Therefore, Compton's discovery was one of the decisive proofs of the correctness of the young quantum theory.

We decided to try something similar, but in optics. discovered by Indian scientists. They wanted to pass light through a substance and see how its rays would be scattered on the molecules of the substance and whether their wavelength would change.

As you can see, willingly or unwillingly, Indian scientists have set themselves the same task as Soviet scientists. But their goals were different. In Calcutta, they were looking for an optical analogy of the Compton effect. In Moscow - experimental confirmation Mandelstam's prediction of frequency changes when light is scattered by fluctuating inhomogeneities.

Raman and Krishnan designed a complex experiment because the expected effect was extremely small. The experiment required a very bright light source. And then they decided to use the sun, collecting its rays using a telescope.

The diameter of its lens was eighteen centimeters. The researchers directed the collected light through a prism onto vessels that contained liquids and gases that were thoroughly cleaned of dust and other contaminants.

But to detect the expected small wavelength extension of scattered light using white sunlight, containing virtually all possible wavelengths, was hopeless. Therefore, scientists decided to use light filters. They placed a blue-violet filter in front of the lens and observed the scattered light through a yellow-green filter. They rightly decided that what the first filter would let through would get stuck in the second. After all, the yellow-green filter absorbs the blue-violet rays transmitted by the first filter. And both, placed one behind the other, should absorb all the incident light. If some rays fall into the eye of the observer, then it will be possible to say with confidence that they were not in the incident light, but were born in the substance under study.

Columbus

Indeed, in the scattered light, Raman and Krishnan detected rays passing through the second filter. They recorded extra frequencies. This could in principle be the optical Compton effect. That is, when scattered on the molecules of a substance located in the vessels, the blue-violet light could change its color and become yellow-green. But this still needed to be proven. There could be other reasons causing the yellow-green light to appear. For example, it could appear as a result of luminescence - a faint glow that often appears in liquids and solids under the influence of light, heat and other causes. Obviously, there was one thing - this light was born again, it was not contained in the falling light.

The scientists repeated their experiment with six different liquids and two types of vapor. They were convinced that neither luminescence nor other reasons play a role here.

The fact that the wavelength of visible light increases when it is scattered in matter seemed established to Raman and Krishnan. It seemed that their search was crowned with success. They discovered an optical analogue of the Compton effect.

But in order for the experiments to have a finished form and the conclusions to be sufficiently convincing, it was necessary to do one more part of the work. It was not enough to detect a change in wavelength. It was necessary to measure the magnitude of this change. The first step was helped by a light filter. He was powerless to do the second. Here scientists needed a spectroscope - a device that allows them to measure the wavelength of the light being studied.

And the researchers began the second part, no less complex and painstaking. But she also satisfied their expectations. The results again confirmed the conclusions of the first part of the work. However, the wavelength turned out to be unexpectedly large. Much more than expected. This did not bother the researchers.

How can we not remember Columbus here? He sought to find sea ​​route to India and, having seen the land, had no doubt that he had achieved his goal. Did he have reason to doubt his confidence at the sight of the red inhabitants and the unfamiliar nature of the New World?

Isn't it true that Raman and Krishnan, in their quest to discover the Compton effect in visible light, thought they had found it by examining light passing through their liquids and gases?! Did they doubt when measurements showed an unexpectedly larger change in the wavelength of the scattered rays? What conclusion did they draw from their discovery?

According to Indian scientists, they found what they were looking for. On March 23, 1928, a telegram with an article entitled “Optical analogy of the Compton effect” flew to London. The scientists wrote: “Thus, the optical analogy of the Compton effect is obvious, except that we are dealing with a change in wavelength much larger...” Note: “much larger...”

Dance of atoms

The work of Raman and Krishnan was greeted with applause among scientists. Everyone rightly admired their experimental art. For this discovery, Raman was awarded the Nobel Prize in 1930.

Attached to the letter from the Indian scientists was a photograph of the spectrum, on which the lines depicting the frequency of the incident light and the light scattered on the molecules of the substance took their places. This photograph, according to Raman and Krishnan, illustrated their discovery more clearly than ever.

When Mandelstam and Landsberg looked at this photograph, they saw an almost exact copy of the photograph they had received! But, having become acquainted with her explanation, they immediately realized that Raman and Krishnan were mistaken.

No, Indian scientists did not discover the Compton effect, but a completely different phenomenon, the same one that Soviet scientists had been studying for many years...

While the excitement caused by the discovery of Indian scientists was growing, Mandelstam and Landsberg were finishing control experiments and summing up the final decisive results.

And so on May 6, 1928, they sent an article to print. A photograph of the spectrum was attached to the article.

Having briefly outlined the history of the issue, the researchers gave a detailed interpretation of the phenomenon they discovered.

So what was this phenomenon that caused many scientists to suffer and rack their brains?

Mandelstam's deep intuition and clear analytical mind immediately told the scientist that the detected changes in the frequency of scattered light could not be caused by those intermolecular forces that equalize random repetitions of air density. It became clear to the scientist that the reason undoubtedly lies inside the molecules of the substance themselves, that the phenomenon is caused by intramolecular vibrations of the atoms that form the molecule.

Such fluctuations occur with much more high frequency, than those that accompany the formation and resorption of random inhomogeneities in the environment. It is these vibrations of atoms in molecules that affect the scattered light. The atoms seem to mark it, leave their traces on it, and encrypt it with additional frequencies.

It was a beautiful guess, a daring invasion of human thought beyond the cordon of the small fortress of nature - the molecule. And this reconnaissance brought valuable information about its internal structure.

Hand in hand

So, while trying to detect a small change in the frequency of scattered light caused by intermolecular forces, a larger change in frequency was discovered caused by intramolecular forces.

Thus, to explain the new phenomenon, which was called “Raman scattering of light,” it was enough to supplement the theory of molecular scattering created by Mandelstam with data on the influence of vibrations of atoms inside molecules. The new phenomenon was discovered as a result of the development of Mandelstam’s idea, formulated by him back in 1918.

Yes, not without reason, as Academician S.I. said. Vavilov, “Nature gifted Leonid Isaakovich with a completely unusual visionary subtle mind, who immediately noticed and understood the main thing, which the majority passed by indifferently. This is how the fluctuation essence of light scattering was understood, and this is how the idea of ​​a change in the spectrum during light scattering appeared, which became the basis for the discovery of Raman scattering.”

Subsequently, enormous benefits were derived from this discovery and it received valuable practical application.

At the moment of its discovery, it seemed only a most valuable contribution to science.

What about Raman and Krishnan? How did they react to the discovery of Soviet scientists, and to their own too? Did they understand what they had discovered?

The answer to these questions is contained in the following letter from Raman and Krishnan, which they sent to the press 9 days after the publication of the article by Soviet scientists. Yes, they realized that the phenomenon they observed was not the Compton effect. This is Raman scattering of light.

After the publication of the letters of Raman and Krishnan and the articles of Mandelstam and Landsberg, it became clear to scientists around the world that the same phenomenon was independently and almost simultaneously made and studied in Moscow and Calcutta. But Moscow physicists studied it in quartz crystals, and Indian physicists studied it in liquids and gases.

And this parallelism, of course, was not accidental. She talks about the relevance of the problem and its great scientific importance. It is not surprising that results close to the conclusions of Mandelstam and Raman at the end of April 1928 were also independently obtained by the French scientists Rocard and Kaban. After some time, scientists remembered that back in 1923, the Czech physicist Smekal theoretically predicted the same phenomenon. Following the work of Smekal, theoretical research by Kramers, Heisenberg, and Schrödinger appeared.

Apparently, only a lack of scientific information can explain the fact that scientists in many countries worked on solving the same problem without even knowing it.

Thirty seven years later

Raman studies have not only discovered new chapter in the science of light. At the same time, they gave powerful weapons to technology. Industry has an excellent way to study the properties of matter.

After all, the frequencies of Raman scattering of light are imprints that are superimposed on the light by the molecules of the medium that scatters the light. And in different substances these prints are not the same. This is what gave Academician Mandelstam the right to call Raman scattering of light the “language of molecules.” To those who can read the traces of molecules on rays of light and determine the composition of scattered light, molecules, using this language, will tell about the secrets of their structure.

On the negative of a Raman spectrum photograph there is nothing but lines of varying blackness. But from this photograph, a specialist will calculate the frequencies of intramolecular vibrations that appeared in the scattered light after it passed through the substance. The picture will tell about many hitherto unknown sides inner life molecules: about their structure, about the forces that bind atoms into molecules, about relative movements atoms. By learning to decipher Raman spectrograms, physicists learned to understand the peculiar “light language” with which molecules tell about themselves. So the new discovery allowed us to penetrate deeper into internal structure molecules.

Today, physicists use Raman scattering to study the structure of liquids, crystals and glassy substances. Chemists use this method to determine the structure of various compounds.

Methods for studying matter using the phenomenon of Raman scattering of light were developed by employees of the laboratory of the P.N. Physical Institute. Lebedev Academy of Sciences of the USSR, which was headed by Academician Landsberg.

These methods make it possible to quickly and accurately produce quantitative and qualitative analyzes aviation gasolines, cracking products, petroleum products and many other complex organic liquids. To do this, it is enough to illuminate the substance under study and use a spectrograph to determine the composition of the light scattered by it. It seems very simple. But before this method turned out to be truly convenient and fast, scientists had to work a lot to create accurate, sensitive equipment. And that's why.

From total number Of the light energy entering the substance under study, only an insignificant part - approximately one ten-billionth - accounts for the share of scattered light. And Raman scattering rarely accounts for even two or three percent of this value. Apparently, this is why Raman scattering itself remained unnoticed for a long time. It is not surprising that obtaining the first Raman photographs required exposures lasting tens of hours.

Modern equipment created in our country makes it possible to obtain a Raman spectrum pure substances within a few minutes and sometimes even seconds! Even for the analysis of complex mixtures, in which individual substances are present in amounts of several percent, an exposure time of no more than an hour is usually sufficient.

Thirty-seven years have passed since the language of molecules recorded on photographic plates was discovered, deciphered and understood by Mandelstam and Landsberg, Raman and Krishnan. Since then, hard work has been going on around the world to compile a “dictionary” of the language of molecules, which opticians call a catalog of Raman frequencies. When such a catalog is compiled, the decoding of spectrograms will be greatly facilitated and Raman scattering will become even more fully at the service of science and industry.