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.
The main fact concerns sunlight. Sunlight is known to be white. White is the sum of all spectra. It can be decomposed into rainbows (or spectra) as it passes through a dispersion medium.
Based on this fact, scientists have proposed several theories.
First theory attributed the blue color to scattering by particles in the atmosphere. It was assumed that a large amount of mechanical dust, particles of plant pollen, water vapor and other small inclusions work as a dispersion medium. As a result, only the bluish color spectrum reaches us. But how then to explain that the color of the sky does not change in winter or in the north, where there are fewer such particles or their nature is different? The theory was quickly rejected.
Next theory assumed that the light flux of white color passes through the atmosphere, which consists 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. For now, 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.
Municipal budgetary educational institution
"Kislovskaya secondary school" of the Tomsk region
Research
Topic: “Why is the sunset red…”
(light dispersion)
Work completed: ,
5A class student
Supervisor;
chemistry teacher
1. Introduction ………………………………………………… 3
2. Main part……………………………………………… 4
3. What is light…………………………………………….. 4
Subject of study- sunset and sky.
Research hypotheses:
The sun has rays that paint the sky in different colors;
Red color can be obtained in the laboratory.
The relevance of my topic lies in the fact that it will be interesting and useful for listeners because so many people look at the clear blue sky, admire it, and few know why it is so blue during the day, and red at sunset and what gives him such a color.
2. Main body
At first glance, this question seems simple, but in fact it touches on the deep aspects of the refraction of light in the atmosphere. Before understanding the answer to this question, it is necessary to have an idea of what light is..jpg" align="left" height="1 src=">
What is light?
Sunlight is energy. The heat of the sun's rays, focused by the lens, turns into fire. Light and heat are reflected by white surfaces and absorbed by black ones. That's why white clothes colder than black.
What is the nature of light? The first person to seriously study light was Isaac Newton. He believed that light consists of particles of corpuscles, which are shot like bullets. But some characteristics of light could not be explained by this theory.
Another scientist, Huygens, offered another explanation for the nature of light. He developed the "wave" theory of light. He believed that light generates impulses, or waves, in the same way that a stone thrown into a pond creates waves.
What views do scientists hold today on the origin of light? It is now believed that light waves have the characteristic features of both particles and waves at the same time. Experiments are underway to support both theories.
Light is made up of photons, weightless particles that have no mass, travel at about 300,000 km/s, and have wave properties. The frequency of wave vibrations of light determines its color. In addition, the higher the oscillation frequency, the shorter the wavelength. Each color has its own vibration frequency and wavelength. White sunlight is made up of many colors that can be seen when it is refracted through a glass prism.
1. A prism decomposes light.
2. White light is complex.
If you look closely at the passage of light through a triangular prism, you can see that the decomposition of white light begins as soon as the light passes from air into glass. Instead of glass, you can take other materials that are transparent to light.
It is remarkable that this experience has survived centuries, and its methodology is still used in laboratories without significant changes.
dispersion (lat.) - scattering, scattering - dispersion
Newton on dispersion.
I. Newton was the first to study the phenomenon of light dispersion and is considered one of his most important scientific merits. It is not for nothing that on his tombstone, erected in 1731 and decorated with figures of young men who hold the emblems of his most important discoveries, one figure holds a prism, and the inscription on the monument contains the words: “He investigated the difference in light rays and the various properties that appear in this case, which no one suspected before. The last statement is not entirely accurate. The dispersion was known before, but it has not been studied in detail. Being engaged in the improvement of telescopes, Newton drew attention to the fact that the image given by the lens is colored at the edges. Investigating the edges colored by refraction, Newton made his discoveries in the field of optics.
Visible spectrum
When a white beam is decomposed in a prism, a spectrum is formed in which radiation of different wavelengths is refracted at different angles. The colors included in the spectrum, that is, those colors that can be obtained by light waves of one wavelength (or a very narrow range), are called spectral colors. The main spectral colors (having their own name), as well as the emission characteristics of these colors, are presented in the table:
Each “color” in the spectrum must be associated with a light wave of a certain length.
The simplest idea of the spectrum can be obtained by looking at a rainbow. White light, refracted in water droplets, forms a rainbow, since it consists of many rays of all colors, and they are refracted in different ways: red is the weakest, blue and violet are the strongest. Astronomers study the spectra of the Sun, stars, planets, comets, because a lot can be learned from the spectra.
Nitrogen" href="/text/category/azot/" rel="bookmark">nitrogen . Red and blue light interact differently with oxygen. Since the wavelength of blue is approximately the size of an oxygen atom, and because of this, blue light is scattered by oxygen in different directions, while red light easily passes through the atmospheric layer.In fact, violet light is scattered even more in the atmosphere, but the human eye is less susceptible to it than to blue light.As a result, it turns out that the eye a person is caught from all sides by the blue light scattered by oxygen, which makes the sky appear blue to us.
Without an atmosphere on Earth, the Sun would appear to us as a bright white star, and the sky would be black.
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unusual phenomena
https://pandia.ru/text/80/039/images/image008_21.jpg" alt="(!LANG:Aurora Borealis" align="left" width="140" height="217 src=">!} auroras Since ancient times, people have admired the majestic picture of the auroras and wondered about their origin. One of the earliest references to auroras is found in Aristotle. In his "Meteorology", written 2300 years ago, one can read: "Sometimes on clear nights there are many phenomena in the sky - gaps, gaps, blood-red color ...
It looks like it's on fire."
What does the ray of clear night vibrate?
What thin flame strikes into the firmament?
Like lightning without menacing clouds
Strives from the earth to the zenith?
How can it be that a frozen ball
Was there a fire in the middle of winter?
What is aurora? How is it formed?
Answer. Aurora is a luminescent glow that occurs as a result of the interaction of charged particles (electrons and protons) flying from the Sun with atoms and molecules of the earth's atmosphere. The appearance of these charged particles in certain regions of the atmosphere and at certain heights is the result of the interaction of the solar wind with the Earth's magnetic field.
Aerosol "href="/text/category/ayerozolmz/" rel="bookmark">aerosol scattering of dust and moisture, these are the main reason for the decomposition of the sun's color (dispersion). At the zenith position, the fall of the sun's beam on the aerosol components of air occurs almost at a right angle, their layer between the eyes of the observer and the sun is negligible.The lower the sun goes down to the horizon, the more the thickness of the layer increases atmospheric air and the amount of aerosol suspension in it. The sun's rays, relative to the observer, change the angle of incidence on the suspension particles, and then the dispersion of sunlight is observed. So, as mentioned above, sunlight is made up of seven primary colors. Each color, like an electromagnetic wave, has its own length and ability to scatter in the atmosphere. The main colors of the spectrum are arranged on a scale in order, from red to violet. The red color has the least ability to scatter (hence, absorb) in the atmosphere. With the phenomenon of dispersion, all colors that follow red on the scale are scattered by the components of the aerosol suspension and absorbed by them. The observer sees only red. This means that the thicker the layer of atmospheric air, the higher the density of the suspension, the more rays of the spectrum will be scattered and absorbed. Known a natural phenomenon: after the powerful eruption of the Krakatau volcano in 1883, unusually bright, red sunsets were observed in different places on the planet for several years. This is due to the powerful release of volcanic dust into the atmosphere during the eruption.
I don't think my research will end there. I have more questions. I want to know:
What happens when light rays pass through various liquids, solutions;
How light is reflected and absorbed.
After completing this work, I was convinced how much amazing and useful for practical activities can be in the phenomenon of refraction of light. It was it that allowed me to understand why the sunset is red.
Literature
1., Physics. Chemistry. 5-6 cells. Textbook. M.: Bustard, 2009, p.106
2. Bulat phenomena in nature. M.: Enlightenment, 1974, 143 p.
3. "Who makes the rainbow?" - Quant 1988, No. 6, p. 46.
4. Lectures on optics. Tarasov in nature. - M.: Enlightenment, 1988
Internet resources:
1. http://potomy. en/ Why is the sky blue?
2. http://www. voprosy-kak-i-pochemu. en Why is the sky blue?
3. http://experience. en/category/education/
Joy to see and understand
is the most beautiful gift of nature.
Albert Einstein
Mystery of the Sky Blue
Why the sky is blue?...
There is no such person who has not thought about this at least once in his life. Medieval thinkers tried to explain the origin of the color of the sky. Some of them suggested that blue was the true color of air or some of its constituent gases. Others thought that the real color of the sky was black, the way it looks at night. During the day, the black color of the sky is added to the white - the sun's rays, and it turns out ... 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 mixing colors were still unclear. They were installed only three hundred years ago by Newton.
Newton also became interested in the mystery of the azure sky. He began by rejecting all previous theories.
First, he argued, a mixture of white and black never forms blue. Secondly, blue is not the true color of the air at all. If this were the case, then the Sun and Moon at sunset would not appear red, as they really are, but blue. The peaks of distant snowy mountains would have looked like this.
Imagine that the air is colored. Even if it's very weak. Then a thick layer of it would act like colored glass. And if you look through colored glass, then all objects will appear the same color as this glass. Why do distant snowy peaks seem pink to us, and not blue at all?
In a 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 azure sky. He was confused by the rainbow, one of the most beautiful, poetic phenomena of nature. Why does it suddenly appear and just as suddenly disappear? Newton could not be satisfied with the prevailing superstition: a rainbow is a sign from above, it portends good weather. He sought to find the material cause of each phenomenon. He also found the cause of the rainbow.
A rainbow is the result of the refraction of light in raindrops. Realizing this, Newton was able to calculate the shape of the rainbow arc and explain the sequence of colors in the rainbow. His theory could not explain only the occurrence of a double rainbow, but it was not possible to do this until three centuries later with the help of a very complex theory.
The success of the rainbow theory mesmerized Newton. He mistakenly concluded that the blue color of the sky and the rainbow were due to the same cause. A rainbow really flares up when the sun's rays 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 the smallest water bubbles, which, according to his theory, form only the blue part of the rainbow, float in the air in any weather. But this was a delusion.
First decision
Almost 200 years have passed, and another English scientist, Rayleigh, took up this issue, not being afraid that even the great Newton was beyond the power of the task.
Rayleigh studied optics. And people who have devoted their lives to the study of light spend a lot of time in the dark. Extraneous light interferes with the subtlest experiments, so the windows of the optical laboratory are almost always covered with black, impenetrable curtains.
Rayleigh remained alone for hours in his gloomy laboratory with beams of light escaping from the instruments. In the path of the rays, they swirled like living dust particles. They were brightly lit and therefore stood out against a dark background. The scientist, perhaps for a long time in thought, followed their smooth movements, just as a person watches the sparks in a fireplace.
Were it not these dust particles dancing in the rays of light that suggested to Rayleigh a new idea about the origin of the color of the sky?
Even in ancient times, it became known that light propagates in a straight line. This important discovery could already be made primitive watching how, breaking through the cracks of the hut, the sun's rays fall on the walls and floor.
But he was hardly bothered by the thought of why he sees light rays, looking at them from the side. And here is something to think about. After all, sunlight is a beam from the crack to the floor. The eye of the observer is located aside and, nevertheless, sees this light.
We also see the light from a searchlight aimed at the sky. This means that part of the light somehow deviates from the direct path and goes to our eye.
What makes him turn off the path? It turns out that the same dust particles that fill the air. Rays that are scattered by a speck of dust enter our eye, which, meeting obstacles, turn off the road and propagate in a straight line from the scattering speck to our eye.
“Are these dust particles coloring the sky blue?” Rayleigh thought one day. He did the math, and the hunch turned into certainty. He found an explanation for the blue color of the sky, red dawns and blue haze! Well, of course, the smallest dust particles, whose dimensions are smaller than the wavelength of light, scatter sunlight and the stronger the shorter the wavelength, Rayleigh announced in 1871. And since violet and blue rays in the visible solar spectrum have the shortest wavelength, they scatter the most strongly, giving the sky a blue color.
The Sun and the snowy peaks obeyed Rayleigh's calculation. They even confirmed the theory of the scientist. At sunrise and sunset, when sunlight passes through the greatest thickness of the air, violet and blue rays, says Rayleigh's theory, are scattered most strongly. At the same time, they deviate from the direct path and do not fall into the eyes of the observer. The observer sees mainly red rays, which scatter much weaker. Therefore, at sunrise and sunset, the sun appears red to us. For the same reason, the peaks of distant snowy mountains also appear pink.
Looking at the clear sky, we see blue-blue rays that deviate from a 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 that a beautiful explanation? Rayleigh himself was so carried away by it, scientists were so amazed at the harmony of the theory and Rayleigh's victory over Newton, that none of them noticed one simple thing. And this trifle, however, should have completely changed their assessment.
Who will deny that away 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. So... don't dust particles scatter light? Then what?
He again revised all his calculations and made sure that his equations were correct, but this means that dust particles are really not scattering particles. In addition, the dust particles that are present in the air are much larger than the wavelength of light, and Rayleigh's calculations convinced Rayleigh that a large accumulation of them does not enhance the blueness of the sky, but, on the contrary, weakens it. 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 by large particles, both the scattered and transmitted light remain white, so the appearance of large particles in the air gives the sky a whitish color, and the accumulation of a large number of large droplets causes the white color of clouds and fog. This is easy to check on a regular cigarette. The smoke coming out of it from the side of the mouthpiece always appears whitish, and the smoke rising from its burning end has a bluish color.
The smallest particles of smoke rising from the burning end of a cigarette are smaller than the wavelength of light, and, in accordance with Rayleigh's theory, scatter predominantly violet and blue. 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 about the same. That is why the smoke coming from the side of the mouthpiece seems whitish.
Yes, it was useless to argue and defend a theory based on dust particles.
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 all the more pure and bright, the purer the atmosphere, he reasoned, then the color of the sky cannot be due to 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!
Rayleigh was very careful this time. Before reporting his new idea, he decided to test it, somehow check the theory with experience.
The chance presented itself in 1906. Rayleigh was helped by the American astrophysicist Abbott, who studied the blue glow of the sky at the observatory on Mount Wilson. Processing the results of measuring the brightness of the sky glow on the basis of the Rayleigh scattering theory, Abbott calculated the number of molecules contained in each cubic centimeter air. It turned out to be a huge number! Suffice it to say that if you distribute these molecules to all people inhabiting the globe, then everyone will get more than 10 billion of these molecules. In short, Abbott found that every cubic centimeter of air at normal atmospheric temperature and pressure contained 27 billion times a billion molecules.
The number of molecules in a cubic centimeter of gas can be determined in different ways on the basis of completely different and independent phenomena. All of them 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 served as a measure and control in explaining the phenomena occurring in gases.
And now the number obtained by Abbot when measuring the glow of the sky, coincided with Loschmidt's number with great accuracy. But he used the Rayleigh scattering theory in his calculations. Thus, it clearly proved that the theory is correct, that molecular scattering of light does exist.
It seemed that Rayleigh's theory was reliably confirmed by experience; all scholars considered it impeccable.
It became universally recognized and entered into all textbooks of optics. It was possible to breathe easy: finally, an explanation was found for the phenomenon - so familiar and at the same time mysterious.
It is all the more surprising that in 1907 the question was again raised on the pages of a well-known scientific journal: why is the sky blue?!
Dispute
Who dared to question the generally accepted Rayleigh theory?
Oddly enough, it was one of the most ardent fans and admirers of Rayleigh. Perhaps no one appreciated and understood Rayleigh as much, did not know his work so well, was not interested in his scientific work as the young Russian physicist Leonid Mandelstam.
- In the nature of the mind of Leonid Isaakovich, - later recalled another Soviet scientist, Academician N.D. Papaleksi - had a lot in common with Rayleigh. And it is no coincidence that the paths of their scientific creativity often went in parallel and repeatedly crossed.
They crossed themselves this time, in the question of the origin of the color of the sky. Prior to this, Mandelstam was mainly fond of radio engineering. For the beginning of our century, this was a completely new field of science, and few people understood it. After the discovery of A.S. Popov (in 1895), only a few years had passed, and there was an endless amount of work. In a short period, Mandelstam carried out a lot of serious research in the field of electromagnetic oscillations in relation to radio engineering devices. In 1902 he defended his dissertation and at the age of twenty-three he received the degree of Doctor of Natural Philosophy from the University of Strasbourg.
Dealing with the issues of excitation of radio waves, Mandelstam naturally studied the works of Rayleigh, who was a recognized authority in the study of oscillatory processes. And the young doctor involuntarily got acquainted with the problem of coloring the sky.
But, having become acquainted with the problem of coloring the sky, Mandelstam not only showed the fallacy, or, as he himself said, the "insufficiency" of the generally recognized Rayleigh theory of molecular light scattering, not only revealed the secret of the blue color of the sky, but also laid the foundation for research that led to one of major discoveries physics of the 20th century.
And 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, she captivated him with its reticence and internal paradoxes, which, to the surprise of the young physicist, the old, highly experienced Rayleigh did not notice. The insufficiency of Rayleigh's theory was especially clearly revealed in the analysis of another theory built on its basis by Planck to explain the attenuation of light when it passes through an optically homogeneous transparent medium.
In this theory, it was taken as a basis that the molecules of the substance through which light passes are the sources of secondary waves. To create these secondary waves, Planck argued, a part of the energy of the passing wave is spent, which is then weakened. 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 to consider the waves on the surface of the water. If a wave meets stationary or floating objects (piles, logs, boats, etc.), then small waves scatter in all directions from these objects. This is nothing but scattering. Part of the energy of the incident wave is spent on the excitation of secondary waves, which are quite analogous to scattered light in optics. In this case, the initial wave is weakened - it decays.
Floating objects can be much smaller than the wavelength traveling through water. Even small grains will cause secondary waves. Of course, as the size of the particles decreases, the secondary waves they form weaken, but they will still take the energy of the main wave.
This is how Planck imagined the process of weakening of a light wave when 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 consider it more carefully. So, even small grains floating on the surface of the water are sources of secondary waves. But what happens if you pour these grains so thickly that they cover the entire surface of the water? Then it will turn out that the individual secondary waves, caused by numerous grains, will add up in such a way that they completely extinguish those parts of the waves that run to the sides and back, and the scattering will stop. There will be only 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 some 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 whether they move 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 in such a small area as the wavelength of light, a very large number of molecules are contained. It turned out that in this case, secondary light waves excited by individual randomly 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 somewhat lower speed. This disproved the theory of Rayleigh, who believed that the motion 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 whole majestic building shook and threatened to collapse.
Coincidence
But what about the determination of the Loschmidt number from measurements of the blue sky glow? After all, the experiment confirmed the Rayleigh theory of scattering!
“This coincidence must be regarded as accidental,” Mandelstam wrote in 1907 in his work “On Optically Homogeneous and Turbid Media.”
Mandelstam showed that the random motion of molecules cannot make a gas homogeneous. On the contrary, in a real gas there are always the smallest rarefaction and compaction, which are formed as a result of chaotic thermal motion. It is they who lead to the scattering of light, as they violate the optical uniformity 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 dimensions of the inhomogeneities arising as a result of chaotic motion are smaller than the wavelength 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. The theoretical part was developed by Rayleigh. The physical nature of scatterers was established 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 that light is scattered in it. He realized that the blue color of the sky proves that the homogeneity of gases is only apparent. More precisely, gases appear to be homogeneous only when examined by crude instruments, such as a barometer, scales, or other instruments, which are affected by many billions of molecules at once. But a light beam senses incomparably smaller quantities of molecules, measured only in tens of thousands. And this is enough to establish undeniably that the density of a gas is continuously subject to small local changes. Therefore, a homogeneous medium from our “rough” point of view is in fact inhomogeneous. From the "point of view of light" it appears cloudy and therefore scatters light.
Random local changes in the properties of matter, resulting from the thermal motion 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, later developed by Smoluchovsky, Lorentz, Einstein and himself into a new major department of physics - statistical physics.
The sky must shimmer!
So, the secret of the blue color of the sky was revealed. But the study of light scattering did not stop there. Drawing attention to the almost imperceptible changes in air density and explaining the coloration of the sky by fluctuation scattering of light, Mandelstam, with his sharpened instinct as 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, the density of clots, varies with time. Therefore, the scientist argued, the intensity should also change with time - the strength of the scattered light! After all, the denser the clusters of molecules, the more intense the light scattered on them. And since these clots appear and disappear randomly, the sky, simply speaking, should flicker! The strength of its glow and its color should change all the time (but very weakly)! But has anyone ever noticed such a flicker? Of course not.
This effect is so subtle that you can't see it with the naked eye.
None of the scientists also observed such a change in the glow of the sky. Nor did Mandelstam himself have the opportunity to verify the conclusions of his theory. The organization of the most complex experiments was hindered at first by meager conditions tsarist Russia and then the difficulties of the first years of the revolution, foreign intervention and civil war.
In 1925, Mandelstam became the head of a department at Moscow University. Here he met the outstanding scientist and skilled experimenter Grigory Samuilovich Landsberg. And so, connected by deep friendship and common scientific interests, together they continued the assault on the secrets hidden in the weak rays of diffused light.
The optical laboratories of the university in those years were still very poor in instruments. The university did not have a single instrument capable of detecting the flickering of the sky or those small differences in the frequencies of the incident and scattered light that the theory predicted were the result of this flickering.
However, this did not stop the researchers. They abandoned the idea of imitating the sky in the laboratory. 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 search for those frequencies close to it, which should arise during scattering. In addition, the theory suggested that observations were easier to make in solids, since the molecules in them are located much closer than in gases, and the denser the substance, the greater the scattering.
A painstaking search for the most suitable materials began. Finally, the choice fell on quartz crystals. Simply because large transparent quartz crystals are more affordable than any other.
The preparatory experiments lasted two years, 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 spectral analysis equipment, the scientists chose an ingenious workaround that was supposed to make it possible to use the available instruments.
The main difficulty in this work was that the weak light caused by molecular scattering was superimposed by a much stronger light scattered by small impurities and other defects of those crystal samples that could be obtained for experiments. The researchers decided to take advantage of the fact that scattered light, formed by crystal defects and reflections from various parts of the setup, 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 isolate the light of a changed frequency caused by molecular scattering against the background of this much brighter light.
In order for the scattered light to have a value that can be registered, the scientists decided to illuminate the quartz with the most powerful lighting device available to them: a mercury lamp.
So, the light scattered in a crystal must consist of two parts: a weak light of a changed frequency due to molecular scattering (the study of this part was the goal of scientists), and a much stronger light of an unchanged frequency caused by extraneous causes (this part was harmful, it made research difficult.
The idea of the method was attractive due to its simplicity: it is necessary to absorb light of a constant frequency and let only light of a changed frequency pass 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 with mercury vapor. As a result, all the "harmful" light "stuck" in the vessel, and the "useful" light passed without noticeable weakening. In this case, the experimenters took advantage of one already known circumstance. An atom of matter, according to quantum physics, is capable of emitting light waves of only quite certain frequencies. However, this atom is also capable of absorbing light. And 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 of an electrical discharge that occurs inside the lamp. If this light is passed through a vessel also containing mercury vapour, 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 the mercury vapor unharmed. Mercury atoms will not even pay attention to it. That part of the light of the mercury lamp, which 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. The scientists illuminated the 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. Scientists have found not at all what they expected, not what was predicted by theory. They discovered a completely new phenomenon. But what? And isn't that a mistake? Unexpected frequencies were found in scattered light, but much higher and lower frequencies. In the spectrum of scattered light, a whole combination of frequencies appeared, which were not in the light incident on 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 it was impossible not to admire them.
- Leonid Isaakovich sometimes solved very difficult technical problems so beautifully and sometimes brilliantly simply, that involuntarily each of us had a question: “Why didn’t this occur to me before?” - says one of the employees.
A variety of control experiments stubbornly confirmed that there was no error. In the photographs of the spectrum of the scattered light, weak and, nevertheless, 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 the “foreign” frequencies come from in the scattered light?!
And the day came when an amazing insight dawned on Mandelstam. It was an amazing discovery, the one that is now considered one of the most important discoveries of the 20th century.
But both Mandelstam and Landsberg came to the unanimous decision that this discovery could be published only after a solid verification, 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 Ch.N. Raman and K.S. Krishnan sent a telegram from Calcutta to this journal with a short description of his discovery.
In those years, letters about the most diverse discoveries flocked to the journal "Priroda" from all over the world. But not every report is destined to cause excitement among scientists. When the issue with the letter of Indian scientists came out of print, physicists were very excited. Even the title of the note - "A new type of 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 the physicists of the whole world awaited the new letters from Calcutta.
Their interest was fueled to no small extent by the very personality of one of the authors of the discovery, Raman. This is a man of curious fate and an outstanding 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 the university was forced to serve in the Department of Finance for ten years and only after that was invited to the department of the University of Calcutta. Raman soon became the recognized head of the Indian school of physics.
Shortly before the events described, Raman and Krishnan were carried away by a curious task. Then the passions caused in 1923 by the discovery of the American physicist Compton, who, studying the passage of X-rays through matter, had not subsided yet, discovered that part of these rays, scattering away from the original direction, increases their wavelength. Translated into the language of opticians, 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.
Something similar, but already in optics, we decided to try. discover Indian scientists. They wanted to pass light through a substance and see how its rays would scatter on the molecules of the substance and whether their wavelength would change.
As you can see, willingly or unwittingly, Indian scientists set themselves the same task as Soviet scientists. But their goals were different. Calcutta was looking for an optical analogy of the Compton effect. In Moscow - an experimental confirmation of Mandelstam's prediction of a change in frequency when light is scattered by fluctuating inhomogeneities.
Raman and Krishnan conceived a difficult experiment, since the expected effect was to be extremely small. For the experiment, a very bright light source was needed. And then they decided to use the sun, collecting its rays with a telescope.
The diameter of his lens was equal to eighteen centimeters. The researchers directed the collected light through a prism to vessels in which liquids and gases were placed, thoroughly cleaned of dust and other contaminants.
But detecting the expected small wavelength of scattered light using white sunlight, containing almost all possible wavelengths, was hopeless. Therefore, scientists decided to use light filters. They put a blue-violet filter in front of the lens, and observed the scattered light through a yellow-green filter. They rightly decided that what passes through the first filter gets 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, must absorb all the incident light. If, however, some rays fall into the eye of the observer, then it will be possible to say with certainty that they were not in the incident light, but were born in the substance under study.
Columba
Indeed, Raman and Krishnan found rays in scattered light passing through the second filter. They fixed the extra frequencies. This could in principle be the optical Compton effect. That is, when scattered by the molecules of the substance 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 appearance of yellow-green light. For example, it could appear as a result of luminescence - a weak glow that often occurs 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 incident light.
The scientists repeated their experiment with six different liquids and two types of vapors. They made sure that neither luminescence nor other causes play a role here.
The fact that the wavelength of visible light increases when it is scattered in matter seemed to Raman and Krishnan established. It seemed that their search was crowned with success. They discovered an optical analogy to the Compton effect.
But in order for the experiments to have a finished form and the conclusions to be convincing enough, one more part of the work had to be done. It was not enough to detect a change in wavelength. It was necessary to measure the magnitude of this change. The first helped to make a light filter. He was powerless to do the second. Here, scientists needed a spectroscope - a device that allows you to measure the wavelength of the light under study.
And the researchers began the second part, no less complex and painstaking. But she also lived up to 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 didn't bother the researchers.
How not to remember Columbus here? He sought to find a sea route to India and, seeing the land, had no doubt that he had reached his goal. Did he have reason to doubt his confidence at the sight of the red-skinned inhabitants and the unfamiliar nature of the New World?
Isn't it true that Raman and Krishnan, seeking to discover the Compton effect in visible light, decided that they found it by examining the light that passed through their liquids and gases?! Did they doubt when measurements showed unexpectedly greater change 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 flew to London with an article entitled "The Optical Analogy of the Compton Effect". 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 greater ...”
Dance of the Atoms
The work of Raman and Krishnan was met with a standing ovation among scientists. Everyone rightly admired their experimental art. For this discovery, Raman was awarded the Nobel Prize in 1930.
A photograph of the spectrum was attached to the letter of the Indian scientists, on which the lines representing 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 photo, they saw an almost exact copy of the photo they had taken! 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 have 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 last decisive results.
And on May 6, 1928, they sent an article to print. A photograph of the spectrum was attached to the article.
Briefly outlining the history of the issue, the researchers gave a detailed interpretation of the phenomenon they discovered.
So what was this phenomenon that made many scientists suffer and break their heads?
Mandelstam's deep intuition and clear analytical mind immediately prompted the scientist that the discovered changes in the frequency of scattered light cannot be caused by those intermolecular forces that even out the random repetitions of air density. It became clear to the scientist that the reason undoubtedly lies within the molecules of the substance themselves, that the phenomenon is caused by intramolecular vibrations of the atoms that form the molecule.
Such fluctuations occur at a much higher frequency than those that accompany the formation and resorption of random inhomogeneities in the medium. It is these vibrations of atoms in molecules that affect the scattered light. Atoms, as it were, mark it, leave their traces on it, encrypt it with additional frequencies.
It was a most beautiful guess, a daring invasion of human thought beyond the cordon of a small fortress of nature - molecules. And this exploration brought valuable information about its internal structure.
Hand in hand
So, when trying to detect a small change in the frequency of scattered light caused by intermolecular forces, a larger change in frequency caused by intramolecular forces was found.
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 effect 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. Vavilov, “Nature endowed Leonid Isaakovich with a completely unusual perspicacious 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, it received valuable practical application.
At the moment of discovery, it seemed only the 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 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 understood 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 all over the world that the same phenomenon was independently and almost simultaneously done and studied in Moscow and Calcutta. But Moscow physicists studied it in quartz crystals, while Indian physicists studied it in liquids and gases.
And this parallelism, of course, was not accidental. She speaks about the urgency of the problem, 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, the theoretical research of Kramers, Heisenberg, and Schrödinger appeared.
Apparently, only a lack of scientific information can explain the fact that scientists from many countries were working on solving the same problem, without even knowing about it.
Thirty seven years later
Investigations of Raman scattering not only opened a new chapter in the science of light. At the same time, they gave a powerful weapon to technology. The industry has received 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 imprints are not the same. This is what gave Academician Mandelstam the right to call Raman scattering of light the "language of molecules." Those who can read the traces of molecules on the rays of light, determine the composition of scattered light, molecules, using this language, will tell about the secrets of their structure.
On the negative of a photograph of the combination spectrum there is nothing but lines of varying blackness. But from this photograph, the 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 aspects of the inner life of molecules: about their structure, about the forces that bind atoms into molecules, about the relative movements of atoms. By learning to decipher Raman spectrograms, physicists have learned to understand the peculiar "light language" that molecules use to describe themselves. So the new discovery made it possible to penetrate deeper into the internal structure of 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 the study of matter, using the phenomenon of Raman scattering of light, were developed by employees of the laboratory of the P.N. Lebedev Academy of Sciences of the USSR, headed by Academician Landsberg.
These methods make it possible to quickly and accurately perform quantitative and qualitative analyzes of aviation gasolines, cracked products, oil refinery products and many other complex organic liquids in the factory laboratory. To do this, it is sufficient to illuminate the substance under study and determine the composition of the light scattered by it with a spectrograph. It seems very simple. But before this method turned out to be really convenient and fast, scientists had to work hard to create accurate, sensitive equipment. And that's why.
Of the total amount of light energy entering the substance under study, only an insignificant part - approximately one ten-billionth - falls to the fraction 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. And it is not surprising that obtaining the first photographs of Raman scattering required exposures lasting tens of hours.
Modern equipment, created in our country, makes it possible to obtain a Raman spectrum of pure substances within a few minutes, and sometimes even seconds! Even for the analysis of complex mixtures, in which individual substances are included in an amount of several percent, an exposure not exceeding 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, persistent work has been carried out all over the world to compile a "dictionary" of the language of molecules, which opticians call the catalog of Raman frequencies. When such a catalog is compiled, the interpretation of the spectrograms will be greatly facilitated, and Raman scattering of light will become even more fully at the service of science and industry.
Simple explanation
What is the sky?
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 purity.
Sky - it is just air, that ordinary air that we breathe every second, that which cannot be seen and touched, because it is transparent and weightless. But we breathe transparent air, why does it acquire such a blue color overhead? Air contains several elements, nitrogen, oxygen, carbon dioxide, water vapor, various dust particles that are constantly in motion.
From the point of view of physics
In practice, as physicists say, the sky is just air, colored by the sun's rays. Simply put, the sun shines on the Earth, but for this the sun's rays must pass through a huge layer of air that literally envelops the Earth. And so, as the sunbeam has many colors, or rather the 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 splashes different colors of the rainbow in all directions, but the blue color spreads most of all, due to which the sky acquires a blue color. Briefly described, the blue sky is a spray that gives a beam painted 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 still I would not want to see a constantly black sky above my head.
The sky is changing color
The sky is not always blue, it tends to change color. Everyone probably noticed that sometimes it is whitish, sometimes bluish-black ... Why is that? For example, at night, when the sun does not send out 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? (the hypotheses of Goethe, Newton, scientists of the XVIII century, Rayleigh)
What hypotheses were not put forward at different times to explain the color of the sky. Watching how the smoke against the background of a dark fireplace acquires a bluish color, Leonardo da Vinci wrote: “... lightness over darkness becomes blue, the more beautiful, the more excellent 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 largest natural scientist of his time. However, this explanation of the color of the sky turned out to be untenable, since, as it became clear later, mixing black and white can only give gray tones, not colors. The blue color of smoke from a fireplace is due to a completely different process.
After the discovery of interference, in particular in thin films, newton tried to apply interference to explain the color of the sky. To do this, he had to admit that the drops of water are in the form of thin-walled bubbles, like soap bubbles. But since the water droplets contained in the atmosphere are in fact spheres, this hypothesis soon "burst" like a soap bubble.
18th century scientists Mariotte, Bouguer, Euler they thought that the blue color of the sky was due to the own color of the constituent parts of the air. This explanation even received some confirmation later, already in the 19th century, when it was established that liquid oxygen has a blue color, and liquid ozone is blue. O.B. came closest to a correct explanation of the color of the sky. Saussure. He believed that if the air were absolutely clean, then the sky would be black, but the air contains impurities that reflect predominantly blue (in particular, water vapor and water droplets). By the second half of the XIX century. a wealth of experimental material has been accumulated on the scattering of light in liquids and gases, in particular, one of the characteristics of the scattered light coming from the sky, its polarization, has been discovered. Arago was the first to discover and explore it. This was in 1809. Later, Babinet, Brewster and other scientists were engaged in studies of the polarization of the firmament. The question of the color of the sky attracted the attention of scientists so much that the ongoing experiments on the scattering of light in liquids and gases, which had a much wider meaning, were carried out from the point of view of “laboratory reproduction of the blue color of the sky.” This is also indicated by the titles of the works: “Simulation of the blue color of the sky "Brucke or "On the blue color of the sky, the polarization of light by cloudy matter in general" by Tyndall. The success of these experiments directed the thoughts of scientists along the right path - to look for the cause of the blue color of the sky in the scattering of sunlight in the atmosphere.
Rayleigh, an English scientist, was the first to create a coherent, rigorous mathematical theory of the molecular scattering of light in the atmosphere. He believed that the scattering of light does not occur on impurities, as his predecessors thought, but on the air molecules themselves. Rayleigh's first work on the scattering of light was published in 1871. In its final form, his theory of scattering, based on the electromagnetic nature of light, established by that time, was presented in the work "On light from the sky, its polarization and color", published in 1899 Rayleigh (his full name is John William Strutt, Lord Rayleigh III) is often called Rayleigh the Scatterer, in contrast to his son, Lord Rayleigh IV, for his work in the field of light scattering Rayleigh IV is called Rayleigh Atmospheric for his great contribution to the development of atmospheric physics. To explain the color of the sky, we will cite only one of the conclusions of Rayleigh's theory, we will refer to others several times when explaining various optical phenomena.This conclusion says: the brightness, or intensity, of scattered light varies inversely with the fourth power of the wavelength of light incident on a scattering particle Thus, molecular scattering is extremely sensitive to the slightest change in the wavelength of light.For example, the wavelength of violet new rays (0.4 μm) are approximately two times smaller than the wavelength of red ones (0.8 μm). Therefore, violet rays will be scattered 16 times more strongly than red ones, and with equal intensity of the 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 amounts inversely proportional to the fourth power of the wavelength of each of them. If now all colored scattered rays are mixed in such a 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 faint yellowish tint, which intensifies as the Sun descends to the horizon. Now the rays have to travel a longer and longer path in the atmosphere. On a long path, the loss of short-wave, i.e., violet, blue, blue, rays becomes more and more noticeable, and in the direct light of the Sun or Moon, predominantly long-wave rays reach the Earth's surface - red, orange, yellow. Therefore, the color of the Sun and Moon becomes first 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 thickness of the atmosphere, mainly long-wave rays (red Sun) remain, short-wave rays (blue sky) fall into scattered light. So Rayleigh's theory very clearly and convincingly explained the riddle of the blue sky and the red Sun.
sky thermal molecular scattering
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Playing on the street, I once drew attention to the sky, it was extraordinary: bottomless, endless and blue, blue! And only the clouds slightly covered this blue color. I wondered why the sky is blue? I immediately remembered the song of the fox Alice from the fairy tale about Pinocchio “What a blue sky ...!” and a geography lesson, where we, studying the topic “Weather”, described the state of the sky, and also said that it was blue. So, why is the sky blue? When I got home, I asked my mother this question. She told me that when people cry, they ask heaven for help. The sky takes away their tears, so it turns blue like a lake. But my mother's story did not satisfy my question. I decided to ask my classmates and teachers if they know why the sky is blue? 24 students and 17 teachers took part in the survey. After processing the questionnaires, the following results were obtained:
At school, in a geography lesson, I asked the teacher this question. She answered me that the color of the sky can be easily explained in terms of physics. This phenomenon is called dispersion. From Wikipedia, I learned that dispersion is the process of decomposing light into a spectrum. Geography teacher Larisa Borisovna suggested that I observe this phenomenon empirically. And we went to the physics room. Vasily Alexandrovich, a teacher of physics, willingly agreed to help us with this. With the help of special equipment, I was able to trace how the process of dispersion occurs in nature.
In order to find the answer to the question why the sky is blue, we decided to conduct a study. This is how the idea for the project was born. With my supervisor, we determined the topic, purpose and objectives of the study, put forward a hypothesis, determined the research methods and mechanisms for implementing our idea.
Hypothesis: the sun sends light to the Earth and most often, when we look at it, it seems to us dazzling white. Does that mean the sky should be white? But the sky is actually blue. In the course of the study, we will find explanations for these contradictions.
Target: find the answer to the question why the sky is blue and find out what determines its color.
Tasks: 1. Get acquainted with the theoretical material on the topic
2. Experimentally study the phenomenon of light dispersion
3. Observe the color of the sky at different times of the day and in different weather
Object of study: sky
Thing: light and color of the sky
Research methods: analysis, experiment, observation
Stages of work:
1. Theoretical
2. Practical
3. Final: conclusions on the research topic
The practical significance of the work: research materials can be used in the lessons of geography and physics as a learning module.
2. The main part.
2.1. Theoretical aspects of the problem. The phenomenon of blue sky in terms of physics
Why is the sky blue - it is very difficult to find the answer to such a simple question. First, let's define the concept. The sky is the space above the Earth or the surface of any other astronomical object. In general, the sky is usually called the panorama that opens when viewed from the surface of the Earth (or other astronomical object) in the direction of space.
Many scientists racked their brains in search of an answer. Leonardo da Vinci, watching the fire in the fireplace, wrote: "Lightness over darkness becomes blue." But today it is known that the fusion of white and black gives gray.
Rice. 1. Hypothesis of Leonardo da Vinci
Isaac Newton almost explained the color of the sky, however, for this he had to admit that the water drops contained in the atmosphere have thin walls like soap bubbles. But it turned out that these drops are spheres, which means that they do not have a wall thickness. So Newton's bubble burst!
Rice. 2. Newton's hypothesis
The best solution to the problem about 100 years ago was proposed by the English physicist Lord John Rayleigh. But let's start from the beginning. The sun emits a dazzling white light, which means that the color of the sky should be the same, but it is still blue. What happens to white light in the atmosphere? It, passing through the atmosphere, as through a prism, breaks up into seven colors. You probably know these lines: every hunter wants to know where the pheasant is sitting. These sentences have a deep meaning. They represent the primary colors in the visible light spectrum.
Rice. 3. Spectrum of white light.
The best natural display of this spectrum is, of course, the rainbow.
Rice. 4 Visible light spectrum
Visible light is electromagnetic radiation whose waves have different wavelengths. There is also invisible light, which our eyes do not perceive. These are ultraviolet and infrared. We can't see it because its length is either too long or too short. To see light means to perceive its color, but what color we will see depends on the wavelength. The longest visible wavelengths are red and the shortest wavelengths are purple.
The ability of light to scatter, that is, to propagate in a medium, also depends on the wavelength. Red light waves scatter the worst, but blue and violet colors have a high scattering ability.
Rice. 5. The ability of light to scatter
And finally, we have come close to answering our question, why is the sky blue? As mentioned above, white is a mixture of all possible colors. when colliding with a gas molecule, each of the seven color components of white light is scattered. In this case, light with longer wavelengths is scattered worse than light with short wavelengths. Because of this, 8 times more blue spectrum remains in the air than red. Although purple has the shortest wavelength, the sky still appears blue due to the mixture of purple and green waves. In addition, our eyes perceive blue better than purple, with the same brightness of both. It is these facts that determine the color scheme of the sky: the atmosphere is literally filled with blue-blue rays.
However, the sky is not always blue. During the day we see the sky blue, blue, gray, in the evening - red (Appendix 1). Why is the sunset red? During sunset, the Sun approaches the horizon, and the sun's beam is directed to the Earth's surface not vertically, as during the day, but at an angle. Therefore, the path it takes through the atmosphere is much longer than what it takes during the day when the Sun is high. Because of this, the blue-blue spectrum is absorbed in the atmosphere before reaching the Earth, and longer light waves of the red spectrum reach the Earth's surface, coloring the sky in red and yellow tones. The change in the color of the sky is clearly related to the rotation of the Earth around its axis, which means the angle of incidence of light on the Earth.
2.2. Practical aspects. An experimental way to solve the problem
In the physics classroom, I got acquainted with the spectrograph device. Vasily Alexandrovich, a teacher of physics, told me the principle of operation of this device, after which I independently conducted an experiment called dispersion. A beam of white light passing through a prism is refracted and we see a rainbow on the screen (Appendix 2). This experience helped me understand how this amazing creation of nature appears in the sky. With the help of a spectrograph, scientists today can obtain information about the composition and properties of various substances.
Photo 1. Demonstration of dispersion experience in
physics classroom
I also wanted to get a rainbow at home. My geography teacher, Larisa Borisovna, told me how to do this. A glass container with water, a mirror, a flashlight and a white sheet of paper became an analogue of the spectrograph. We put a mirror in a container with water, put a white sheet of paper behind the container. We direct the light of a flashlight onto the mirror so that the reflected light falls on the paper. A rainbow appeared on a piece of paper again! (Appendix 3). The experiment is best done in a darkened room.
We have already said above that white light, in fact, already contains all the colors of the rainbow. Make sure of this and, to collect all the colors back to white, you can make a rainbow top (Appendix 4). If you spin it hard, the colors will merge and the disc will turn white.
Despite the scientific explanation for the formation of a rainbow, this phenomenon remains one of the mysterious optical spectacles in the atmosphere. Watch and enjoy!
3. Conclusion
In search of an answer to the children's question so often asked by parents "Why is the sky blue?" I learned a lot of interesting and instructive things for myself. The contradictions in our hypothesis today have a scientific explanation:
The whole secret is in the color of the sky in our atmosphere - in air shell planet Earth.
The white ray of the sun, passing through the atmosphere, breaks up into rays of seven colors.
The red and orange rays are the longest, while the blue ones are the shortest.
Blue rays reach the Earth less than others, and thanks to these rays, the sky is pierced with blue.
The sky is not always blue and this is due to the axial movement of the Earth.
Empirically, we were able to visualize and understand how dispersion occurs in nature. At class time at school, I told my classmates why the sky is blue. It was also interesting to know where the phenomenon of dispersion can be observed in our Everyday life. I have found several practical applications for this unique phenomenon. (Appendix 5). In the future, I would like to study the sky further. How much more is it fraught with mysteries? What phenomena still occur in the atmosphere and what is their nature? How do they affect humans and all living things on Earth? Perhaps this will be the topic of my future research.
Bibliography
1. Wikipedia - the free encyclopedia
2. L.A. Malikov. Electronic manual on physics "Geometric optics"
3. Peryshkin A.V. Physics. Grade 9 Textbook. M.: Bustard, 2014, p.202-209
4.http;/www. voprosy-kak-ipochemu.ru
5. Personal photo archive "Sky over Golyshmanovo"
Appendix 1.
"The sky over Golyshmanovo"(personal photo archive)
Appendix 2
Light dispersion using a spectrograph
Appendix 3
Dispersion of light at home
"rainbow"
Appendix 4
rainbow top
Top at rest Spinning top during rotation
Appendix 5
Dispersion in a person's life
Diamond Lights aboard an aircraft
car headlights
Reflective signs