Died on June 3. Parachute birthday

“Optical phenomena in nature”

Introduction

a) The concept of optics

b) Classification of optics

c) Optics in the development of modern physics

Phenomena associated with the reflection of light

4. Auroras

Introduction

Optics concept

The first ideas of ancient scientists about light were very naive. They thought that visual impressions arise when objects are felt with special thin tentacles that come out of the eyes. Optics was the science of vision, this is how this word can most accurately be translated.

Gradually in the Middle Ages, optics turned from the science of vision into the science of light, facilitated by the invention of lenses and the camera obscura. At the present time, optics is a branch of physics that studies the emission of light and its propagation in various media, as well as its interaction with matter. Issues related to vision, the structure and functioning of the eye, became a separate scientific field - physiological optics.

Optics classification

Light rays – geometric lines, along which light energy propagates, when considering many optical phenomena, one can use the idea of them. In this case, we talk about geometric (ray) optics. Geometric optics has become widespread in lighting engineering, as well as when considering the actions of numerous instruments and devices - from magnifying glasses and glasses to the most complex optical telescopes and microscopes.

Intensive research into the previously discovered phenomena of interference, diffraction and polarization of light began at the beginning of the 19th century. These processes were not explained within the framework of geometric optics, so it was necessary to consider light in the form of transverse waves. As a result, wave optics appeared. Initially, it was believed that light is elastic waves in a certain medium (world ether) filling the world space.

But the English physicist James Maxwell in 1864 created the electromagnetic theory of light, according to which light waves are electromagnetic waves with a corresponding range of lengths.

And already at the beginning of the 20th century, new studies showed that in order to explain some phenomena, for example the photoelectric effect, there is a need to represent a light beam in the form of a stream of peculiar particles - light quanta. Isaac Newton had a similar view on the nature of light 200 years ago in his “theory of the effusion of light.” Now quantum optics is doing this.

The role of optics in the development of modern physics.

Optics also played a significant role in the development of modern physics. The emergence of two of the most important and revolutionary theories of the twentieth century (quantum mechanics and the theory of relativity) is connected in principle with optical research. Optical methods for analyzing matter at the molecular level have given rise to a special scientific field - molecular optics, which also includes optical spectroscopy, used in modern materials science, plasma research, and astrophysics. There are also electron and neutron optics.

At the present stage of development, an electron microscope and a neutron mirror have been created, and optical models of atomic nuclei have been developed.

Optics, influencing the development of various areas of modern physics, is itself today in a period of rapid development. The main impetus for this development was the invention of lasers - intense sources of coherent light. As a result, wave optics rose to a higher level, the level of coherent optics.

Thanks to the advent of lasers, many scientific and technical developing areas have emerged. Among which are nonlinear optics, holography, radio optics, picosecond optics, adaptive optics, etc.

Radio optics originated at the intersection of radio engineering and optics and deals with the study of optical methods for transmitting and processing information. These methods are combined with traditional electronic methods; The result was a scientific and technical direction called optoelectronics.

The subject of fiber optics is the transmission of light signals through dielectric fibers. Using the achievements of nonlinear optics, it is possible to change the wavefront of a light beam, which is modified as light propagates in a particular medium, for example, in the atmosphere or in water. Consequently, adaptive optics has emerged and is being intensively developed. Closely related to this is photoenergetics, which is emerging before our eyes and deals, in particular, with the issues of efficient transmission of light energy along a beam of light. Modern laser technology makes it possible to produce light pulses with a duration of only picoseconds. Such pulses turn out to be a unique “tool” for studying a number of fast processes in matter, and in particular in biological structures. A special direction has emerged and is being developed – picosecond optics; Photobiology is closely related to it. It can be said without exaggeration that widespread practical use of the achievements of modern optics is a prerequisite scientific and technological progress. Optics opened the way to the microworld for the human mind, and it also allowed it to penetrate the secrets star worlds. Optics covers all aspects of our practice.

Phenomena associated with the reflection of light.

The object and its reflection

The fact that the landscape reflected in still water does not differ from the real one, but is only turned upside down, is far from true.

If a person looks late in the evening at how lamps are reflected in the water or how the shore descending to the water is reflected, then the reflection will seem shortened to him and will completely “disappear” if the observer is high above the surface of the water. Also, you can never see the reflection of the top of a stone, part of which is immersed in water.

The landscape appears to the observer as if it were viewed from a point located as much below the surface of the water as the observer's eye is above the surface. The difference between the landscape and its image decreases as the eye approaches the surface of the water, and also as the object moves away.

People often think that the reflection of bushes and trees in a pond has brighter colors and richer tones. This feature can also be noticed by observing the reflection of objects in a mirror. Here psychological perception plays a greater role than the physical side of the phenomenon. The frame of the mirror and the banks of the pond limit a small area of the landscape, protecting a person’s lateral vision from excess scattered light coming from the entire sky and blinding the observer, that is, he looks at a small area of the landscape as if through a dark narrow pipe. Reducing the brightness of reflected light compared to direct light makes it easier for people to observe the sky, clouds and other brightly lit objects that, when directly observed, are too bright for the eye.

Dependence of reflection coefficient on the angle of incidence of light.

At the boundary of two transparent media, light is partially reflected, partially passes into another medium and is refracted, and partially absorbed by the medium. The ratio of reflected energy to incident energy is called the reflection coefficient. The ratio of the energy of light transmitted through a substance to the energy of incident light is called transmittance.

Reflection and transmittance coefficients depend on the optical properties, the adjacent media and the angle of incidence of light. So, if light falls on a glass plate perpendicularly (angle of incidence α = 0), then only 5% of the light energy is reflected, and 95% passes through the interface. As the angle of incidence increases, the fraction of reflected energy increases. At the angle of incidence α=90˚ it is equal to unity.

The dependence of the intensity of light reflected and transmitted through a glass plate can be traced by placing the plate at different angles to the light rays and assessing the intensity by eye.

It is also interesting to evaluate by eye the intensity of light reflected from the surface of a reservoir, depending on the angle of incidence, to observe the reflection sun rays from the windows of the house at different angles of incidence during the day, at sunset, at sunrise.

Safety glasses

Conventional window glass partially transmits heat rays. This is good for use in northern areas, as well as for greenhouses. In the south, the rooms become so overheated that it is difficult to work in them. Protection from the Sun comes down to either shading the building with trees, or choosing a favorable orientation of the building during reconstruction. Both are sometimes difficult and not always feasible.

To prevent glass from transmitting heat rays, it is coated with thin transparent films of metal oxides. Thus, a tin-antimony film does not transmit more than half of thermal rays, and coatings containing iron oxide completely reflect ultraviolet rays and 35-55% of thermal rays.

Solutions of film-forming salts are applied from a spray bottle to the hot surface of the glass during its heat treatment or molding. At high temperatures, salts transform into oxides, tightly bound to the surface of the glass.

Glasses for sunglasses are made in a similar way.

Total internal reflection of light

A beautiful sight is the fountain, whose ejected jets are illuminated from within. This can be depicted under normal conditions by performing the following experiment (Fig. 1). In a tall tin can, drill a round hole at a height of 5 cm from the bottom ( A) with a diameter of 5-6 mm. The light bulb with the socket must be carefully wrapped in cellophane paper and placed opposite the hole. You need to pour water into the jar. Opening the hole A, we get a jet that will be illuminated from within. In a dark room it glows brightly and looks very impressive. The stream can be given any color by placing colored glass in the path of the light rays b. If you put your finger in the path of the stream, the water splashes and these droplets glow brightly.

The explanation for this phenomenon is quite simple. A ray of light passes along a stream of water and hits a curved surface at an angle greater than the limiting one, experiences total internal reflection, and then again hits the opposite side of the stream at an angle again greater than the limiting one. So the beam passes along the jet, bending along with it.

But if the light were completely reflected inside the jet, then it would not be visible from the outside. Part of the light is scattered by water, air bubbles and various impurities present in it, as well as due to the uneven surface of the jet, so it is visible from the outside.

Cylindrical light guide

If you direct a light beam at one end of a solid glass curved cylinder, you will notice that light will come out of its other end (Fig. 2); Almost no light comes out through the side surface of the cylinder. The passage of light through a glass cylinder is explained by the fact that, falling on the inner surface of the cylinder at an angle greater than the limiting one, the light undergoes complete reflection many times and reaches the end.

The thinner the cylinder, the more often the beam will be reflected and the larger part of the light will fall on the inner surface of the cylinder at angles greater than the limiting one.

Diamonds and gems

There is an exhibition of the Russian diamond fund in the Kremlin.

The light in the hall is slightly dimmed. The jewelers' creations sparkle in the windows. Here you can see such diamonds as “Orlov”, “Shah”, “Maria”, “Valentina Tereshkova”.

The secret of the wonderful play of light in diamonds is that this stone has a high refractive index (n=2.4173) and, as a result, a small angle of total internal reflection (α=24˚30′) and has greater dispersion, causing the decomposition of white light to simple colors.

In addition, the play of light in a diamond depends on the correctness of its cut. The facets of a diamond reflect light multiple times within the crystal. Due to the great transparency of high-class diamonds, the light inside them almost does not lose its energy, but only decomposes into simple colors, the rays of which then burst out in various, most unexpected directions. When you turn the stone, the colors emanating from the stone change, and it seems that it itself is the source of many bright multi-colored rays.

There are diamonds colored red, bluish and lilac. The shine of a diamond depends on its cut. If you look through a well-cut water-transparent diamond into the light, the stone appears completely opaque, and some of its facets appear simply black. This happens because the light, undergoing total internal reflection, comes out in the opposite direction or to the sides.

When viewed from the side of the light, the top cut shines with many colors and is shiny in places. The bright sparkle of the upper edges of a diamond is called diamond luster. The underside of the diamond appears to be silver-plated from the outside and has a metallic sheen.

The most transparent and large diamonds serve as decoration. Small diamonds are widely used in technology as a cutting or grinding tool for metalworking machines. Diamonds are used to reinforce the heads of drilling tools for drilling wells in hard rocks. This use of diamond is possible due to its great hardness. Other precious stones in most cases are crystals of aluminum oxide with an admixture of oxides of coloring elements - chromium (ruby), copper (emerald), manganese (amethyst). They are also distinguished by hardness, durability and have beautiful colors and “play of light”. Currently, they are able to artificially obtain large crystals of aluminum oxide and paint them in the desired color.

The phenomena of light dispersion are explained by the variety of colors of nature. A whole set of optical experiments with prisms was carried out by the English scientist Isaac Newton in the 17th century. These experiments showed that white light is not fundamental, it should be considered as composite (“inhomogeneous”); the main ones are different colors (“uniform” rays, or “monochromatic” rays). The decomposition of white light into different colors occurs because each color has its own degree of refraction. These conclusions made by Newton are consistent with modern scientific ideas.

Along with the dispersion of the refractive index, dispersion of the absorption, transmission and reflection coefficients of light is observed. This explains the various effects when illuminating bodies. For example, if there is some body transparent to light, for which the transmittance coefficient is large for red light and the reflection coefficient is small, but for green light it is the opposite: the transmittance coefficient is small and the reflection coefficient is large, then in transmitted light the body will appear red, and in reflected light it is green. For example, chlorophyll has such properties - green substance, contained in plant leaves and causing green color. A solution of chlorophyll in alcohol appears red when viewed against light. In reflected light, the same solution appears green.

If a body has a high absorption coefficient and low transmittance and reflection coefficients, then such a body will appear black and opaque (for example, soot). A very white, opaque body (eg magnesium oxide) has a reflectance close to unity for all wavelengths, and very low transmittance and absorption coefficients. A body (glass) that is completely transparent to light has low reflection and absorption coefficients and a transmittance close to unity for all wavelengths. In colored glass, for some wavelengths the transmittance and reflection coefficients are practically equal to zero and, accordingly, the absorption coefficient for the same wavelengths is close to unity.

Phenomena associated with the refraction of light

Some types of mirages. From the larger variety of mirages, we will single out several types: “lake” mirages, also called lower mirages, upper mirages, double and triple mirages, ultra-distant vision mirages.

Lower (“lake”) mirages appear above a very heated surface. Superior mirages, on the contrary, appear above a very cool surface, for example above cold water. If the lower mirages are observed, as a rule, in deserts and steppes, then the upper ones are observed in northern latitudes.

The upper mirages are diverse. In some cases they give a direct image, in other cases an inverted image appears in the air. Mirages can be double, when two images are observed, one simple and one inverted. These images may be separated by a strip of air (one may be above the horizon line, the other below it), but may directly merge with each other. Sometimes another one appears - a third image.

Ultra-long-range vision mirages are especially amazing. K. Flammarion in his book “Atmosphere” describes an example of such a mirage: “Based on the testimony of several trustworthy persons, I can report on a mirage that was seen in the city of Verviers (Belgium) in June 1815. One morning, residents of the city saw in the sky army, and it was so clear that one could distinguish the suits of the artillerymen and even, for example, a cannon with a broken wheel that was about to fall off... It was the morning of the Battle of Waterloo!” The described mirage is depicted in the form of a colored watercolor by one of the eyewitnesses. The distance from Waterloo to Verviers in a straight line is more than 100 km. There are known cases when similar mirages were observed at large distances - up to 1000 km. “The Flying Dutchman” should be attributed precisely to such mirages.

Explanation of the lower (“lake”) mirage. If the air near the surface of the earth is very hot and, therefore, its density is relatively low, then the refractive index at the surface will be less than in higher air layers. Changing the refractive index of air n with height h near the earth's surface for the case under consideration is shown in Figure 3, a.

In accordance with the established rule, light rays near the surface of the earth will be in in this case bend so that their trajectory is convex downward. Let there be an observer at point A. A light ray from a certain area of the blue sky will enter the observer's eye, experiencing the specified curvature. This means that the observer will see the corresponding section of the sky not above the horizon line, but below it. It will seem to him that he sees water, although in fact there is an image of blue sky in front of him. If we imagine that there are hills, palm trees or other objects near the horizon line, then the observer will see them upside down, thanks to the noted curvature of the rays, and will perceive them as reflections of the corresponding objects in non-existent water. This is how an illusion arises, which is a “lake” mirage.

Simple superior mirages. It can be assumed that the air at the very surface of the earth or water is not heated, but, on the contrary, is noticeably cooled compared to higher air layers; the change in n with height h is shown in Figure 4, a. In the case under consideration, the light rays are bent so that their trajectory is convex upward. Therefore, now the observer can see objects hidden from him behind the horizon, and he will see them at the top, as if hanging above the horizon line. Therefore, such mirages are called upper.

The superior mirage can produce both an upright and an inverted image. The direct image shown in the figure occurs when the refractive index of air decreases relatively slowly with height. When the refractive index decreases rapidly, an inverted image is formed. This can be verified by considering a hypothetical case - the refractive index at a certain height h decreases abruptly (Fig. 5). The rays of the object, before reaching observer A, experience total internal reflection from the boundary BC, below which in this case there is denser air. It can be seen that the superior mirage gives an inverted image of the object. In reality, there is no abrupt boundary between the layers of air; the transition occurs gradually. But if it occurs sharply enough, then the superior mirage will give an inverted image (Fig. 5).

Double and triple mirages. If the refractive index of air changes first quickly and then slowly, then in this case the rays in region I will bend faster than in region II. As a result, two images appear (Fig. 6, 7). Light rays 1 propagating within the air region I form an inverted image of the object. Rays 2, which propagate mainly within region II, are bent to a lesser extent and form a straight image.

To understand how a triple mirage appears, you need to imagine three successive air regions: the first (near the surface), where the refractive index decreases slowly with height, the next, where the refractive index decreases quickly, and the third region, where the refractive index decreases again slowly. The figure shows the considered change in the refractive index with height. The figure shows how a triple mirage occurs. Rays 1 form the lower image of the object, they extend within the air region I. Rays 2 form an inverted image; I fall into air region II, these rays experience strong curvature. Rays 3 form the upper direct image of the object.

Ultra-long-range vision mirage. The nature of these mirages is least studied. It is clear that the atmosphere must be transparent, free of water vapor and pollution. But this is not enough. A stable layer of cooled air should form at a certain height above the earth's surface. Below and above this layer the air should be warmer. A light beam that gets inside a dense cold layer of air is, as it were, “locked” inside it and spreads through it as if through a kind of light guide. The beam path in Figure 8 is always convex towards less dense areas of air.

The occurrence of ultra-long-range mirages can be explained by the propagation of rays inside similar “light guides”, which nature sometimes creates.

Rainbow is a beautiful celestial phenomenon that has always attracted human attention. In former times, when people still knew little about the world around them, the rainbow was considered a “heavenly sign.” So, the ancient Greeks thought that the rainbow was the smile of the goddess Iris.

A rainbow is observed in the direction opposite to the Sun, against the background of rain clouds or rain. The multi-colored arc is usually located at a distance of 1-2 km from the observer, and sometimes it can be observed at a distance of 2-3 m against the background of water drops formed by fountains or water sprays.

The center of the rainbow is located on the continuation of the straight line connecting the Sun and the observer's eye - on the antisolar line. The angle between the direction towards the main rainbow and the anti-solar line is 41-42º (Fig. 9).

At the moment of sunrise, the antisolar point (point M) is on the horizon line and the rainbow has the appearance of a semicircle. As the Sun rises, the antisolar point moves below the horizon and the size of the rainbow decreases. It represents only part of a circle.

A secondary rainbow is often observed, concentric with the first, with an angular radius of about 52º and the colors in reverse.

When the Sun's altitude is 41º, the main rainbow ceases to be visible and only part of the side rainbow protrudes above the horizon, and when the Sun's altitude is more than 52º, the side rainbow is not visible either. Therefore, in mid-equatorial latitudes this natural phenomenon is never observed during the midday hours.

The rainbow has seven primary colors, smoothly transitioning from one to another.

The type of arc, the brightness of the colors, and the width of the stripes depend on the size of the water droplets and their number. Large drops create a narrower rainbow, with sharply prominent colors, small drops create a blurry, faded and even white arc. That is why a bright narrow rainbow is visible in the summer after a thunderstorm, during which large drops fall.

The rainbow theory was first proposed in 1637 by Rene Descartes. He explained rainbows as a phenomenon related to the reflection and refraction of light in raindrops.

The formation of colors and their sequence were explained later, after unraveling the complex nature of white light and its dispersion in the medium. The diffraction theory of rainbows was developed by Erie and Partner.

We can consider the simplest case: let a beam of parallel solar rays fall on drops shaped like a ball (Fig. 10). A ray incident on the surface of a drop at point A is refracted inside it according to the law of refraction:

n sin α=n sin β, where n=1, n≈1.33 –

respectively, the refractive indices of air and water, α is the angle of incidence, and β is the angle of refraction of light.

Inside the drop, the ray AB travels in a straight line. At point B, the beam is partially refracted and partially reflected. It should be noted that the smaller the angle of incidence at point B, and therefore at point A, the lower the intensity of the reflected beam and the greater the intensity of the refracted beam.

Beam AB, after reflection at point B, occurs at an angle β` = β b and hits point C, where partial reflection and partial refraction of light also occurs. The refracted ray leaves the drop at an angle γ, and the reflected ray can travel further, to point D, etc. Thus, the light ray in the drop undergoes multiple reflection and refraction. With each reflection, some of the light rays come out and their intensity inside the drop decreases. The most intense of the rays emerging into the air is the ray emerging from the drop at point B. But it is difficult to observe it, since it is lost against the background of bright direct sunlight. The rays refracted at point C together create a primary rainbow against the background of a dark cloud, and the rays refracted at point D produce a secondary rainbow, which is less intense than the primary one.

When considering the formation of a rainbow, one more phenomenon must be taken into account - the unequal refraction of light waves of different lengths, that is, light rays of different colors. This phenomenon is called dispersion. Due to dispersion, the angles of refraction γ and the angle of deflection Θ of rays in a drop are different for rays of different colors.

Most often we see one rainbow. It is not uncommon for two rainbow stripes to appear in the sky at the same time, located one after the other; still watching larger number celestial arcs - three, four and even five at the same time. This interesting phenomenon was observed by Leningraders on September 24, 1948, when in the afternoon four rainbows appeared among the clouds over the Neva. It turns out that rainbows can arise not only from direct rays; It often appears in the reflected rays of the Sun. This can be seen on the shores of the sea bays, big rivers and lakes. Three or four rainbows - ordinary and reflected - sometimes create a beautiful picture. Since the rays of the Sun reflected from the water surface go from bottom to top, the rainbow formed in the rays can sometimes look completely unusual.

You should not think that rainbows can only be seen during the day. It also happens at night, although it is always weak. You can see such a rainbow after a night rain, when the Moon appears from behind the clouds.

Some semblance of a rainbow can be obtained through the following experiment: You need to illuminate a flask filled with water solar light or a lamp through a hole in a white board. Then a rainbow will become clearly visible on the board, and the angle of divergence of the rays compared to the initial direction will be about 41-42°. Under natural conditions, there is no screen; the image appears on the retina of the eye, and the eye projects this image onto the clouds.

If a rainbow appears in the evening before sunset, then a red rainbow is observed. In the last five or ten minutes before sunset, all the colors of the rainbow except red disappear, and it becomes very bright and visible even ten minutes after sunset.

A rainbow on the dew is a beautiful sight. It can be observed at sunrise on the grass covered with dew. This rainbow is shaped like a hyperbola.

Auroras

One of the most beautiful optical phenomena of nature is the aurora.

In most cases, auroras have a green or blue-green hue with occasional spots or a border of pink or red.

Auroras are observed in two main forms - in the form of ribbons and in the form of cloud-like spots. When the radiance is intense, it takes the form of ribbons. Losing intensity, it turns into spots. However, many tapes disappear before they have time to break into spots. The ribbons seem to hang in the dark space of the sky, resembling a giant curtain or drapery, usually stretching from east to west for thousands of kilometers. The height of this curtain is several hundred kilometers, the thickness does not exceed several hundred meters, and it is so delicate and transparent that the stars are visible through it. The lower edge of the curtain is quite sharply and clearly outlined and is often tinted in a red or pinkish color, reminiscent of a curtain border; the upper edge is gradually lost in height and this creates a particularly impressive impression of the depth of space.

There are four types of auroras:

A homogeneous arc - a luminous stripe has the simplest, calmest shape. It is brighter from below and gradually disappears upward against the background of the sky glow;

Radiant arc - the tape becomes somewhat more active and mobile, it forms small folds and streams;

Radial stripe - with increasing activity, larger folds overlap small ones;

As activity increases, the folds or loops expand to enormous sizes, and the bottom edge of the ribbon glows brightly with a pink glow. When activity subsides, the folds disappear and the tape returns to a uniform shape. This suggests that a homogeneous structure is the main form of the aurora, and folds are associated with increasing activity.

Radiances of a different type often appear. They cover the entire polar region and are very intense. They occur during an increase in solar activity. These auroras appear as a whitish-green cap. Such auroras are called squalls.

Based on the brightness of the aurora, they are divided into four classes, differing from each other by one order of magnitude (that is, 10 times). The first class includes auroras that are barely noticeable and approximately equal in brightness to the Milky Way, while the fourth class auroras illuminate the Earth as brightly as the full Moon.

It should be noted that the resulting aurora spreads to the west at a speed of 1 km/sec. The upper layers of the atmosphere in the area of auroral flashes heat up and rush upward, which affected the increased braking of artificial Earth satellites passing through these zones.

During auroras, eddy electric currents arise in the Earth's atmosphere, covering large areas. They excite magnetic storms, the so-called additional unstable magnetic fields. When the atmosphere shines, it emits X-rays, which are most likely the result of the deceleration of electrons in the atmosphere.

Frequent flashes of radiance are almost always accompanied by sounds reminiscent of noise and crackling. Auroras have big influence to strong changes in the ionosphere, which in turn affect radio communication conditions, i.e. radio communication is greatly deteriorated, resulting in severe interference, or even complete loss of reception.

The emergence of auroras.

The Earth is a huge magnet, the north pole of which is located near the south geographic pole, and the south pole is located near the north. And the lines of force magnetic field Earths are geomagnetic lines extending from the region adjacent to the Earth's north magnetic pole. They cover everything Earth and enter it in the region of the south magnetic pole, forming a toroidal lattice around the Earth.

It was believed for a long period of time that the location of magnetic field lines was symmetrical relative to the earth's axis. But in fact, it turned out that the so-called “solar wind,” i.e., a stream of protons and electrons emitted by the Sun, attacks the geomagnetic shell of the Earth from a height of about 20,000 km. It pulls it away from the Sun, thereby forming a kind of magnetic “tail” on the Earth.

Once in the Earth's magnetic field, an electron or proton moves in a spiral, winding around the geomagnetic line. These particles, falling from the solar wind into the Earth's magnetic field, are divided into two parts: one part along the magnetic field lines immediately flows into the polar regions of the Earth, and the other gets inside the teroid and moves inside it, as can be done according to the left-hand rule, along closed curve ABC. Ultimately, these protons and electrons also flow along geomagnetic lines to the region of the poles, where their increased concentration appears. Protons and electrons produce ionization and excitation of atoms and molecules of gases. They have enough energy for this. Since protons arrive on Earth with energies of 10,000-20,000 eV (1 eV = 1.6 10 J), and electrons with energies of 10-20 eV. But for the ionization of atoms it is necessary: for hydrogen - 13.56 eV, for oxygen - 13.56 eV, for nitrogen - 124.47 eV, and even less for excitation.

Based on the principle that occurs in tubes with rarefied gas when currents are passed through them, excited gas atoms give back the received energy in the form of light.

The green and red glow, according to the results of a spectral study, belongs to excited oxygen atoms, and the infrared and violet glow belongs to ionized nitrogen molecules. Some oxygen and nitrogen emission lines form at an altitude of 110 km, and the red glow of oxygen occurs at an altitude of 200-400 km. The next weak source of red light is hydrogen atoms, formed in the upper layers of the atmosphere from protons arriving from the Sun. Such a proton, after capturing an electron, turns into an excited hydrogen atom and emits red light.

After solar flares, auroral flares usually occur within a day or two. This indicates a connection between these phenomena. Research using rockets has shown that in places of greater intensity of auroras, a higher level of ionization of gases by electrons remains. According to scientists, the maximum intensity of auroras is achieved off the coast of oceans and seas.

There are a number of difficulties for the scientific explanation of all phenomena associated with auroras. That is, the mechanism for accelerating particles to certain energies is not completely known, their trajectories of motion in near-Earth space are not clear, the mechanism for the formation of various types of luminescence is not entirely clear, the origin of sounds is unclear, and not everything agrees quantitatively in the energy balance of ionization and excitation of particles.

Used Books:

“Physics in Nature”, author - L. V. Tarasov, Prosveshchenie Publishing House, Moscow, 1988.
“Optical phenomena in nature”, author - V. L. Bulat, publishing house “Prosveshchenie”, Moscow, 1974.
“Conversations on Physics, Part II”, author - M.I. Bludov, Prosveshchenie Publishing House, Moscow, 1985.
“Physics 10”, authors - G. Ya. Myakishev B. B. Bukhovtsev, Prosveshchenie publishing house, Moscow, 1987.
“Encyclopedic Dictionary of a Young Physicist”, compiled by V. A. Chuyanov, Pedagogika Publishing House, Moscow, 1984.
“Schoolchildren's Handbook on Physics”, compiled by, philological society “Slovo”, Moscow, 1995.
“Physics 11”, N. M. Shakhmaev, S. N. Shakhmaev, D. Sh. Shodiev, Prosveshchenie publishing house, Moscow, 1991.
“Solving problems in physics”, V. A. Shevtsov, Nizhne-Volzhskoe book publishing house, Volgograd, 1999.

Since ancient times, mirages and flickering figures in the air have alarmed and terrified people. Nowadays, scientists have uncovered many secrets of nature, including optical phenomena. They are not surprised by natural mysteries, the essence of which has long been studied. IN high school Today optical phenomena are taught in 8th grade physics, so any student can understand their nature.

Basic Concepts

Scientists of antiquity believed that the human eye sees by feeling objects with the thinnest tentacles. Optics at that time was the study of vision.

In the Middle Ages, optics studied light and its essence.

Today, optics is a branch of physics that studies the propagation of light through various media and its interaction with other substances. All issues related to vision are studied by physiological optics.

Optical phenomena are manifestations of diverse actions performed by rays of light. They are studied by atmospheric optics.

Unusual processes in the atmosphere

Planet Earth is surrounded by a gaseous shell called the atmosphere. Its thickness is hundreds of kilometers. Closer to the Earth, the atmosphere is denser, and thins upward. Physical properties The atmospheric shell is constantly changing, the layers are mixed. Change temperature indicators. Density and degree of transparency shift.

Light rays come from the Sun and other celestial bodies towards the Earth. They pass through the Earth's atmosphere, which for them serves as a specific optical system that changes its characteristics. are reflected, scattered, pass through the atmosphere, and illuminate the earth. Under certain conditions, the path of the rays bends, so various phenomena arise. Physicists consider the most original optical phenomena to be:

sunset of the sun;
the appearance of a rainbow;
northern lights;
mirage;
halo.

Let's take a closer look at them.

Halo around the Sun

The word “halo” itself means “circle” in Greek. What optical phenomenon underlies it?

A halo is a process of light refraction and reflection that occurs in cloud crystals high in the atmosphere. The phenomenon looks like luminous rays near the Sun, limited to a dark interval. Halos usually form before cyclones and can be their precursors.

Water droplets freeze in the air and take on a regular prismatic shape with six sides. Everyone is familiar with the icicles appearing in the lower atmospheric layers. At the top, such ice needles freely fall in the vertical direction. Crystalline ice floes swirl and descend to the ground, while they are parallel to the ground. A person directs vision through crystals, which act as lenses and refract light.

Other prisms are flat or look like stars with six rays. Rays of light hitting the crystals may not undergo refraction or undergo a number of other processes. It rarely happens that all processes are clearly visible; usually one or another part of the phenomenon appears more clearly, while others are poorly represented.

The minor halo is a circle around the sun with a radius of approximately 22 degrees. The color of the circle is reddish from the inside, then flows into yellow, white and mixes with the blue sky. The inner area of the circle is dark. It is formed as a result of light refraction in ice needles flying in the air. The rays in the prisms are deflected at an angle of 22 degrees, so those that passed through the crystals appear to the observer deflected by 22 degrees. Therefore it appears dark.

Red color is refracted less and appears least deviated from the sun. Next comes yellow. Other rays mix and appear white to the eye.

There is a halo with an angle of 46 degrees, it is located around a halo of 22 degrees. Its inner region is also reddish because light undergoes refraction in the ice needles, which are turned 90 degrees toward the sun.

A 90-degree halo is also known; it glows faintly, has almost no color or is colored red on the outside. Scientists have not yet fully studied this species.

Halo around the Moon and other types

This optical phenomenon is often visible if there are light clouds and many miniature crystalline ice floes in the sky. Each such crystal is a kind of prism. Basically their shape is elongated hexagons. Light enters the front crystalline region and exits the opposite region and is refracted 22 degrees.

IN winter time You can see a halo in the cold air near the street lamps. It appears due to the light of a lantern.

A halo can also form around the Sun in frosty, snowy air. Snowflakes are in the air, light passes through the clouds. At sunset this light turns red. In past centuries, superstitious people were horrified by such phenomena.

A halo may appear as a rainbow-colored circle around the Sun. It appears if there are many crystals with six sides in the atmosphere, but they do not reflect, but refract the rays of the sun. Most of At the same time, the rays are scattered, not reaching our gaze. The remaining rays reach human eyes, and we notice a rainbow circle around the Sun. Its radius is approximately 22 degrees or 46 degrees.

False Sun

Scientists noted that the halo circle is always brighter on the sides. This is explained by the fact that a vertical and horizontal halo meet here. False suns may appear where they intersect. This happens especially often when the Sun is close to the horizon, at which time we no longer see part of the vertical circle.

A false sun is also an optical phenomenon, a type of halo. It appears due to ice crystals with six sides, shaped like nails. Such crystals float in the atmosphere in a vertical direction, light is refracted at their side faces.

A third “sun” may also form if only the superficial part of the halo circle is visible above the true sun. It can be a segment of an arc or a luminous spot of an incomprehensible shape. Sometimes false suns are so bright that they cannot be distinguished from the real Sun.

Rainbow

This is the form of an incomplete circle with different colors.

Religions of antiquity were considered from heaven to earth. Aristotle believed that a rainbow appears due to the reflection of drops of sunlight. What other optical phenomenon can delight a person as much as a rainbow does?

In the 17th century, Descartes studied the nature of the rainbow. Later, Newton conducted experiments with light and expanded Descartes' theory, but could not understand the formation of several rainbows and the absence of individual color shades in them.

The complete theory of the rainbow was presented in the 19th century by the English astronomer D. Airy. It was he who managed to reveal all the processes of the rainbow. The theory he developed is still accepted today.

A rainbow appears when the light of the sun hits a curtain of rainwater in the area of the sky opposite the Sun. The center of the rainbow is located at a point on the opposite side of the Sun, that is, it is not visible to the human eye. The arc of the rainbow is the part of the circle around this central point.

The colors in the rainbow are placed in a specific order. He is constant. Red - along the top edge, purple - along the bottom. Between them, the colors are in a strict arrangement. The rainbow does not contain all existing colors. The predominance of green color indicates a transition to favorable weather.

Polar Lights

This is a glow in the upper magnetic layers of the atmosphere due to the interaction of atoms and elements of the solar wind. Typically, auroras have green or blue hues interspersed with pink and red. They may be in the form of a ribbon or a spot. Their bursts are often accompanied by noisy sounds.

Mirage

Simple mirage deceptions are familiar to any person. For example, when driving on heated asphalt, a mirage appears as This does not surprise anyone. What optical phenomenon explains the appearance of mirages? Let's look at this issue in more detail.

A mirage is an optical physical phenomenon in the atmosphere, as a result of which the eye sees objects hidden from view under normal conditions. This is explained by the refraction of a light beam as it flows through air layers. Objects located at a considerable distance may rise or fall relative to their true location, or may become distorted and take on bizarre shapes.

Brocken Ghost

This is a phenomenon in which, at sunset or sunrise, the shadow of a person located on a hill acquires incomprehensible proportions, as it falls on clouds nearby. This is due to the reflection and refraction of light rays by water droplets in foggy conditions. The phenomenon was named after one of the heights of the German Harz Mountains.

St. Elmo's Fire

These are luminous brushes of blue or purple color on the masts of sea vessels. Lights can appear on mountainous heights, on buildings of impressive height. This phenomenon occurs due to electrical discharges at the ends of the conductors due to the fact that the electrical tension increases.

These are the optical phenomena discussed in 8th grade lessons. Let's talk about optical devices.

Designs in optics

Optical devices are devices that convert light radiation. Typically these devices operate in visible light.

All optical devices can be divided into two types:

Devices in which an image is produced on a screen. These are cameras, movie cameras, projection devices.
Devices that interact with the human eye but do not produce images on the screen. These are magnifying glasses, microscopes, telescopes. These devices are considered visual.

A camera is an optical-mechanical device used to obtain images of an object on photographic film. The design of the camera includes a camera and lenses that form the lens. The lens creates an inverted, reduced image of the object, captured on film. This occurs due to the action of light.

The image is initially invisible, but thanks to the developing solution it becomes visible. This image is called a negative, in which light areas appear dark and vice versa. The negative is turned into a positive on photosensitive paper. Using a photo enlarger, the image is enlarged.

A magnifying glass is a lens or lens system designed to magnify objects while viewing them. The magnifying glass is placed next to the eye, and the distance from which the object can be seen clearly is selected. The use of a magnifying glass is based on increasing the angle of view from which an object is viewed.

To obtain greater angular magnification, a microscope is used. In this device, objects are magnified thanks to an optical system consisting of a lens and an eyepiece. First, the angle of view is increased by the lens, then by the eyepiece.

So, we examined the main optical phenomena and devices, their varieties and features.

Optical phenomena in nature: reflection, attenuation, total internal reflection, rainbow, mirage.

Russian State Agrarian University Moscow Agricultural Academy named after K.A. Timiryazev

Topic: Optical phenomena in nature

Performed

Bakhtina Tatyana Igorevna

Teacher:

Momdzhi Sergei Georgievich

Moscow, 2014

1. Types of optical phenomena

3. Total internal reflection

Conclusion

1. Types of optical phenomena

Optical phenomenon of each visible event is the result of the interaction of light and material environments, physical and biological. A green beam of light is an example of an optical phenomenon.

Common optical phenomena often occur due to the interaction of light from the sun or moon with the atmosphere, clouds, water, dust, and other particles. Some of them, like a green beam of light, are such a rare phenomenon that they are sometimes considered mythical.

Optical phenomena include those arising from the optical properties of the atmosphere, the rest of nature (other phenomena); from objects, whether natural or human in nature (optical effects), where our eyes have an entoptic nature of phenomena.

There are many phenomena that arise as a result of either the quantum or wave nature of light. Some of them are quite subtle and observable only through precise measurements using scientific instruments.

In my work I want to consider and talk about optical phenomena associated with mirrors (reflection, attenuation) and atmospheric phenomena (mirage, rainbow, auroras), which we often encounter in the world. Everyday life.

2. Mirror optical phenomena

My light, mirror, tell me...

If we take the simple and precise definition, then Mirror is a smooth surface designed to reflect light (or other radiation). The most famous example is a plane mirror.

The modern history of mirrors dates back to the 13th century, or more precisely, from 1240, when Europe learned to blow glass vessels. The invention of the true glass mirror dates back to 1279, when the Franciscan John Peckham described a method of coating glass with a thin layer of tin.

In addition to mirrors invented and created by man, the list of reflective surfaces is large and extensive: the surface of a reservoir, sometimes ice, sometimes polished metal, just glass, if you look at it from a certain angle, but, nevertheless, it is a man-made mirror that can be called practically ideal reflective surface.

The principle of the path of rays reflected from a mirror is simple if we apply the laws of geometric optics, without taking into account the wave nature of light. A ray of light falls on a mirror surface (we are considering a completely opaque mirror) at an angle alpha to the normal (perpendicular) drawn to the point of incidence of the ray on the mirror. The angle of the reflected beam will be equal to the same value - alpha. A ray incident on a mirror at right angles to the plane of the mirror will be reflected back at itself.

For the simplest - flat - mirror, the image will be located behind the mirror symmetrically to the object relative to the plane of the mirror; it will be virtual, straight and the same size as the object itself.

The fact that the landscape reflected in still water does not differ from the real one, but is only turned upside down, is far from true. If a person looks late in the evening at how lamps are reflected in the water or how the shore descending to the water is reflected, then the reflection will seem shortened to him and will completely “disappear” if the observer is high above the surface of the water. Also, you can never see the reflection of the top of a stone, part of which is immersed in water. The landscape appears to the observer as if it were viewed from a point located as much below the surface of the water as the observer's eye is above the surface. The difference between the landscape and its image decreases as the eye approaches the surface of the water, and also as the object moves away. People often think that the reflection of bushes and trees in a pond has brighter colors and richer tones. This feature can also be noticed by observing the reflection of objects in a mirror. Here psychological perception plays a greater role than the physical side of the phenomenon. The frame of the mirror and the banks of the pond limit a small area of the landscape, protecting a person’s lateral vision from excess scattered light coming from the entire sky and blinding the observer, that is, he looks at a small area of the landscape as if through a dark narrow pipe. Reducing the brightness of reflected light compared to direct light makes it easier for people to observe the sky, clouds and other brightly lit objects that, when viewed directly, are too bright for the eye.

3. Total internal reflection of light

A beautiful sight is the fountain, whose ejected jets are illuminated from within. This can be depicted under normal conditions by performing the following experiment. In a tall tin can, at a height of 5 cm from the bottom, you need to drill a round hole with a diameter of 5-6 mm. The light bulb with the socket must be carefully wrapped in cellophane paper and placed opposite the hole. You need to pour water into the jar. By opening the hole, we get a jet that will be illuminated from the inside. In a dark room it glows brightly and looks very impressive. The stream can be given any color by placing colored glass in the path of the light rays. If you put your finger in the path of the stream, the water splashes and these droplets glow brightly. The explanation for this phenomenon is quite simple. A ray of light passes along a stream of water and hits a curved surface at an angle greater than the limiting one, experiences total internal reflection, and then again hits the opposite side of the stream at an angle again greater than the limiting one. So the beam passes along the jet, bending along with it. But if the light were completely reflected inside the jet, then it would not be visible from the outside. Part of the light is scattered by water, air bubbles and various impurities present in it, as well as due to the uneven surface of the jet, so it is visible from the outside.

I will give here a physical explanation for this phenomenon. Let the absolute refractive index of the first medium be greater than the absolute refractive index of the second medium n1 > n2, that is, the first medium is optically denser. Here the absolute indicators of the media are respectively equal:

Then, if you direct a beam of light from an optically denser medium to an optically less dense medium, then as the angle of incidence increases, the refracted ray will approach the interface between the two media, then go along the interface, and with a further increase in the angle of incidence, the refracted ray will disappear, i.e. .e. the incident beam will be completely reflected by the interface between the two media.

The limiting angle (alpha zero) is the angle of incidence, which corresponds to the angle of refraction of 90 degrees. For water, the limit angle is 49 degrees. For glass - 42 degrees. Manifestations in nature: - air bubbles on underwater plants seem mirror-like - dew drops flash with multi-colored lights - the “play” of diamonds in the rays of light - the surface of the water in a glass will shine when viewed from below through the wall of the glass.

4. Atmospheric optical phenomena

A mirage is an optical phenomenon in the atmosphere: the reflection of light by a boundary between layers of air that are sharply different in density. For an observer, such a reflection means that, together with a distant object (or part of the sky), its virtual image, displaced relative to it, is visible.

That is, a mirage is nothing more than a play of light rays. The fact is that in the desert the earth warms up very much. But at the same time, the air temperature above the ground at different distances from it varies greatly. For example, the temperature of the air layer ten centimeters above ground level is 30-50 degrees less than the surface temperature.

All laws of physics say: light propagates in a homogeneous medium in a straight line. However, under such extreme conditions, the law does not apply. What's going on? At such temperature differences, rays begin to be refracted, and at the ground itself they generally begin to be reflected, thereby creating illusions that we are accustomed to calling mirages. That is, the air near the surface becomes a mirror.

Although mirages are usually associated with deserts, they can often be observed above the water surface, in the mountains, and sometimes even in major cities. In other words, wherever sudden temperature changes occur, these fabulous pictures can be observed.

This phenomenon is quite common. For example, in the largest desert on our planet, about 160 thousand mirages are observed annually.

It is very interesting that although mirages are considered children of deserts, Alaska has long been recognized as the undisputed leader in their occurrence. The colder it is, the clearer and more beautiful the observed mirage.

No matter how common this phenomenon is, it is very difficult to study. Why? Yes, everything is very simple. No one knows where and when he will appear, what he will be like and how long he will live.

After many different records about mirages appeared, naturally, they had to be classified. It turned out that, despite all their diversity, it was possible to identify only six types of mirages: lower (lake), upper (appearing in the sky), side, “Fata Morgana”, ghost mirages and werewolf mirages.

A more complex type of mirage is called Fata Morgana. No explanation has yet been found for it.

Lower (lake) mirage.

These are the most common mirages. They got their name because of the places where they originated. They are observed on the surface of the earth and water.

Superior mirages (distance vision mirages).

This type of mirage is as simple in origin as the previous type. However, such mirages are much more diverse and beautiful. They appear in the air. The most fascinating of them are the famous ghost towns. It is very interesting that they usually represent images of objects - cities, mountains, islands - that are located many thousands of kilometers away.

Side mirages

They appear near vertical surfaces that are strongly heated by the sun. These can be rocky shores of the sea or lake, when the shore is already illuminated by the Sun, but the surface of the water and the air above it are still cold. This type of mirage is a very common occurrence in Lake Geneva.

Fata Morgana

Fata Morgana is the most complex type of mirage. It is a combination of several forms of mirages. At the same time, the objects that the mirage depicts are magnified many times over and are quite distorted. Interestingly, this type of mirage got its name from Morgana, the sister of the famous Arthur. She allegedly took offense at Lancelot for rejecting her. To spite him, she settled in the underwater world and began to take revenge on all men, deceiving them with ghostly visions

Fata Morganas also include numerous “flying Dutchmen”, which are still seen by sailors. They usually show ships that are hundreds or even thousands of kilometers away from observers.

Perhaps there is nothing more to say about the types of mirages.

I would like to add that although this is an extremely beautiful and mysterious sight, it is also very dangerous. I kill mirages and drive my victims crazy. This is especially true for desert mirages. And the explanation of this phenomenon does not make the fate of travelers easier.

However, people are trying to fight this. They create special guides that indicate the places where mirages most often appear, and sometimes their forms.

By the way, mirages are obtained in laboratory conditions.

For example, a simple experiment published in the book by V.V. Mayra “Total reflection of light in simple experiments” (Moscow, 1986), given here detailed description obtaining mirage models in a variety of environments. The easiest way to observe a mirage is in water (Fig. 2). Attach a dark, preferably black, one to the bottom of a white-bottomed vessel. tin can from under the coffee. Looking from top to bottom, almost vertically, along its wall, quickly pour into the jar hot water. The surface of the jar will immediately become shiny. Why? The fact is that the refractive index of water increases with temperature. The water temperature near the hot surface of the jar is much higher than at a distance. So the beam of light is bent in the same way as with mirages in the desert or on hot asphalt. The jar appears shiny to us due to the complete reflection of light.

Every designer wants to know where to download Photoshop.

An atmospheric optical and meteorological phenomenon observed when the Sun (sometimes the Moon) illuminates many water droplets (rain or fog). A rainbow looks like a multi-colored arc or circle made up of the colors of the spectrum (from the outer edge: red, orange, yellow, green, blue, indigo, violet). These are the seven colors that are customarily identified in the rainbow in Russian culture, but it should be borne in mind that in fact the spectrum is continuous, and its colors smoothly transition into each other through many intermediate shades.

The center of the circle described by a rainbow lies on a straight line passing through the observer and the Sun, moreover, when observing a rainbow (unlike a halo), the Sun is always behind the observer, and it is impossible to simultaneously see the Sun and the rainbow without the use of optical devices. For an observer on the ground, a rainbow usually looks like an arc, part of a circle, and the higher the observation point, the more complete it is (from a mountain or an airplane you can see a full circle). When the Sun rises above 42 degrees above the horizon, a rainbow is not visible from the Earth's surface.

Rainbows occur because sunlight refracted and reflected by droplets of water (rain or fog) floating in the atmosphere. These droplets bend light of different colors differently (the refractive index of water for longer wavelength (red) light is less than for short wavelength (violet), so red light is deflected weakest by 137°30", and violet light most strongly by 139°20"). As a result, white light is decomposed into a spectrum (light dispersion occurs). An observer who stands with his back to the light source sees a multi-colored glow that emanates from space along concentric circles (arcs).

Most often, a primary rainbow is observed, in which the light undergoes one internal reflection. The path of the rays is shown in the figure at the top right. In the primary rainbow, the red color is outside the arc, its angular radius is 40-42°.

Sometimes you can see another, less bright rainbow around the first one. This is a secondary rainbow, which is formed by light reflected twice in drops. In a secondary rainbow, the order of colors is “inverted” - violet is on the outside and red is on the inside. The angular radius of the secondary rainbow is 50-53°. The sky between two rainbows is usually noticeably darker, an area called Alexander's Strip.

The appearance of a third-order rainbow in natural conditions is extremely rare. It is believed that there have been only five scientific sighting reports in the last 250 years. this phenomenon. All the more surprising is the appearance in 2011 of a message that it was possible not only to observe a fourth-order rainbow, but also to register it in a photograph. In laboratory conditions, it is possible to obtain rainbows of much higher orders. Thus, in an article published in 1998, it was stated that the authors, using laser radiation, managed to obtain a rainbow of the two hundredth order.

The light from a primary rainbow is 96% polarized along the arc direction. The light from the secondary rainbow is 90% polarized.

On a bright moonlit night, you can also see a rainbow from the Moon. Because the receptors human eye working in low light - “sticks” - do not perceive colors, the lunar rainbow looks whitish; The brighter the light, the more “colorful” the rainbow (color receptors - “cones”) are included in its perception.

Under certain circumstances, you can see a double, inverted, or even ring rainbow. In fact, these are phenomena of another process - the refraction of light in ice crystals scattered in the atmosphere, and belong to the halo. For an inverted rainbow (near-zenith arc, zenith arc - one of the types of halo) to appear in the sky, specific weather conditions characteristic of the North and South Poles are required. An inverted rainbow is formed due to the refraction of light passing through the ice of a thin curtain of clouds at an altitude of 7 - 8 thousand meters. The colors in such a rainbow are also located in reverse: purple is at the top, and red is at the bottom.

Polar Lights

Aurora (northern lights) is the glow (luminescence) of the upper layers of the atmospheres of planets with a magnetosphere due to their interaction with charged particles of the solar wind.

In a very limited area of the upper atmosphere, auroras can be caused by low-energy charged solar wind particles entering the polar ionosphere through the north and south polar cusps. In the northern hemisphere, caspen auroras can be observed over Spitsbergen during the afternoon hours.

When energetic particles of the plasma layer collide with the upper atmosphere, the atoms and molecules of gases included in its composition are excited. The radiation of excited atoms is in the visible range and is observed as the aurora. The spectra of auroras depend on the composition of the planets' atmospheres: for example, if for Earth the brightest are the emission lines of excited oxygen and nitrogen in the visible range, then for Jupiter - the emission lines of hydrogen in the ultraviolet.

Since ionization by charged particles occurs most effectively at the end of the particle’s path and the density of the atmosphere decreases with increasing altitude in accordance with the barometric formula, the height of the appearance of auroras depends quite strongly on the parameters of the planet’s atmosphere, so for the Earth with its sufficient complex composition In the atmosphere, the red glow of oxygen is observed at altitudes of 200-400 km, and the combined glow of nitrogen and oxygen is observed at an altitude of ~110 km. In addition, these factors determine the shape of the auroras - blurry upper and rather sharp lower boundaries.

Auroras are observed mainly at high latitudes of both hemispheres in oval zones-belts surrounding the Earth's magnetic poles - auroral ovals. The diameter of the auroral ovals is ~ 3000 km during a quiet Sun; on the day side, the zone boundary is 10--16° from the magnetic pole, on the night side - 20--23°. Since the Earth’s magnetic poles are separated from the geographic ones by ~12°, auroras are observed at latitudes of 67--70°, however, during times of solar activity, the auroral oval expands and auroras can be observed at lower latitudes - 20--25° south or north of the boundaries of their usual manifestation. For example, on Stewart Island, which lies only at the 47° parallel, auroras occur regularly. The Maori even called it “Burning Ones”.

In the spectrum of the Earth's auroras, the most intense radiation is from the main components of the atmosphere - nitrogen and oxygen, while their emission lines are observed in both the atomic and molecular (neutral molecules and molecular ions) states. The most intense are the emission lines of atomic oxygen and ionized nitrogen molecules.

The glow of oxygen is due to the emission of excited atoms in metastable states with wavelengths of 557.7 nm (green line, lifetime 0.74 sec.) and a doublet of 630 and 636.4 nm (red region, lifetime 110 sec). As a result, the red doublet is emitted at altitudes of 150-400 km, where, due to the high rarefaction of the atmosphere, the rate of quenching of excited states during collisions is low. Ionized nitrogen molecules emit at 391.4 nm (near ultraviolet) 427.8 nm (violet) and 522.8 nm (green). However, each phenomenon has its own unique range, due to the variability of the chemical composition of the atmosphere and weather factors.

The spectrum of auroras changes with altitude and, depending on the emission lines predominant in the aurora spectrum, auroras are divided into two types: high-altitude auroras of type A with a predominance of atomic lines and auroras of type B at relatively low altitudes (80-90 km) with a predominance of molecular lines in the spectrum due to quenching from collisions of atomic excited states in a relatively dense atmosphere at these altitudes.

Auroras occur noticeably more often in spring and autumn than in winter and summer. The peak frequency occurs during periods closest to the spring and autumn equinoxes. During the aurora, a huge amount of energy is released in a short time. Thus, during one of the disturbances recorded in 2007, 5·1014 joules were released, approximately the same as during an earthquake of magnitude 5.5.

When observed from the surface of the Earth, the aurora appears as a general, rapidly changing glow of the sky or moving rays, stripes, coronas, or “curtains.” The duration of aurora ranges from tens of minutes to several days.

The auroras in the northern and southern hemispheres were believed to be symmetrical. However, the simultaneous observation of the aurora in May 2001 from space from the northern and south poles showed that the northern and southern lights are significantly different from each other.

optical light quantum rainbow

Conclusion

Natural optical phenomena are very beautiful and varied. In ancient times, when people did not understand their nature, they gave them mystical, magical and religious meanings, feared and feared them. But now, when we are even able to produce each of the phenomena with our own hands in laboratory (and sometimes even makeshift) conditions, the primitive horror has gone, and we can happily notice a rainbow flashing in the sky in everyday life, go to the north to admire the aurora and to note with curiosity a mysterious mirage glimpsed in the desert. And mirrors have become an even more significant part of our daily life - both in everyday life (for example, at home, in cars, in video cameras), and in various scientific instruments: spectrophotometers, spectrometers, telescopes, lasers, medical equipment.

1. Ponytail

From the outside it may seem that the waterfall is “burning”. In fact, when light hits the waterfall at right angles, it looks like the Ponytail is lighting up.

2. "False Sun"

This illusion is known as the "false sun". And a similar phenomenon occurs when ice crystals in the atmosphere create the effect of two additional suns on either side of the real sun.

3. “Fata Morgana”

This is a very complex type of mirage that often appears similar to real man-made objects. Fata Morgana occurs due to the fact that air masses with different temperatures distort light waves.

4. "Light pillar"

In this case, ice crystals in the air are also to blame for the illusion. A giant vertical beam appears in the sky above the light sources.

5. Brocken Ghost

It is also called the "mountain ghost". This phenomenon occurs when a person's magnified shadow is cast on the clouds or fog that lies below them.

6. "Atlantic Road"

This bridge in Norway looks like a ramp leading to nowhere. This is actually an optical illusion, as the bridge actually curves and “hides” behind the horizon.

7. Moon Illusion

Everyone has noticed that when the Moon is close to the horizon, it appears much larger. But if you look at it through “binoculars” from clasped hands, the Moon will suddenly become smaller. This happens because the brain adjusts the size of the Moon in relation to some other object on the horizon and (wrongly) decides that the Moon should actually be much larger!

8. "Green Ray"

Sometimes this phenomenon occurs just before or after sunset: a green spot or ray appears on the edge of the solar disk for just a few seconds. Although this is caused by various factors, the general explanation is that light is refracted in the atmosphere and causes this effect.

9. Anti-aircraft arc

The next optical phenomenon is similar to a rainbow, but the colors of such an arc are usually much purer. And it is caused, unlike a rainbow, not by raindrops, but by ice crystals.

10. Halo

Halos can often be seen around the Sun or Moon. It looks like a halo surrounding this celestial body.

11. Alpine glow

This interesting phenomenon occurs when the sun has already set below the horizon. Due to the light bouncing off particles in the atmosphere, the mountains sometimes appear to be illuminated with a reddish glow.

12. Aurora Borealis

In the northern hemisphere, the aurora is known as Aurora Borealis, and in the southern hemisphere it is called Aurora Australis. These phenomena are caused by magnetic rays and solar wind interacting with the upper atmosphere.

13. Salt marshes

Salt marshes are found throughout the world. They can cause unusual, illusory depth perception because the person cannot see any landmarks.

14. "Apache Head"

Apache Head is a rock on the French island of Ebian that looks like an Indian head. This phenomenon is known as pareidolia - illusory images based on the details of a real object.

15. "Warden of the Wasteland"

This rock formation in the Canadian province of Alberta can be seen on Google Earth. From above, the mountains look like the head of a man wearing a Canadian aboriginal headdress. Moreover, the mountains look like an “Indian” either wearing earrings or headphones.

16. Cloud with thunderstorm

A cloud with a thunderstorm is one of the most impressive sights. You can see such clouds along the sea coasts and they look, to put it mildly, ominously.

Fans of travel and natural attractions should pay attention to.

The atmosphere is a turbid, optically inhomogeneous medium. Optical phenomena are the result of reflection, refraction and diffraction of light rays in the atmosphere.

Depending on the causes of occurrence, all optical phenomena are divided into four groups:

1) phenomena caused by the scattering of light in the atmosphere (twilight, dawn);

2) phenomena caused by the refraction of light rays in the atmosphere (refraction) - mirages, twinkling of stars, etc.;

3) phenomena caused by the refraction and reflection of light rays on drops and crystals of clouds (rainbow, halo);

4) phenomena caused by the diffraction of light in clouds and fog - crowns, glory.

Twilight caused by the scattering of sunlight in the atmosphere. Twilight is the transition period from day to night (evening twilight) and from night to day (morning twilight). Evening twilight begins from the moment the sun sets and until complete darkness sets in, morning twilight - vice versa.

The duration of twilight is determined by the angle between the direction of the apparent daily movement of the Sun and the horizon; Thus, the duration of twilight depends on geographic latitude: the closer to the equator, the shorter the twilight.

There are three periods of twilight:

1) civil twilight (the sun's descent below the horizon does not exceed 6°) – light;

2) navigation (immersion of the Sun below the horizon up to 12 o) - visibility conditions are greatly deteriorated;

3) astronomical (immersion of the Sun below the horizon to 18 o) - it is already dark at the earth’s surface, but dawn is still noticeable in the sky.

Zarya - a set of colorful light phenomena in the atmosphere observed before sunrise or during sunset. The variety of colors of dawn depends on the position of the Sun relative to the horizon and on the state of the atmosphere.

The color of the sky is determined by the scattered visible rays of the Sun. In a clean and dry atmosphere, light scattering occurs according to Rayleigh's law. Blue rays are scattered about 16 times more strongly than red ones, so the color of the sky (scattered sunlight) is blue, and the color of the Sun and its rays at the horizon is red, because. In this case, light travels a longer path in the atmosphere.

Large particles in the atmosphere (droplets, dust particles, etc.) scatter light neutrally, which is why clouds and fog are white. With high humidity and dust, the entire sky becomes not blue, but whitish. Consequently, by the degree of blueness of the sky one can judge the purity of the air and the nature of the air masses.

Atmospheric refraction – atmospheric phenomena associated with the refraction of light rays. Refraction is caused by: the twinkling of stars, the flattening of the visible disk of the Sun and Moon at the horizon, an increase in the length of the day by several minutes, as well as mirages. A mirage is a visible imaginary image on the horizon, above the horizon or below the horizon, caused by a sharp violation of the density of air layers. There are lower, upper, and lateral mirages. Moving mirages – “Fata Morgana” – are rarely observed.

Rainbow - this is a light arc, painted in all the colors of the spectrum, against the background of a cloud illuminated by the Sun, from which raindrops fall. The outer edge of the arc is red, the inner edge is purple. If the Sun is low above the horizon, then we see only half of the circle. When the Sun is high, the arc becomes smaller, because the center of the circle falls below the horizon. When the Sun's altitude is greater than 42°, the rainbow is not visible. From an airplane you can see a rainbow in an almost complete circle.

A rainbow is formed by the refraction and reflection of sunlight in water droplets. The brightness and width of the rainbow depends on the size of the droplets. Large droplets produce a smaller but brighter rainbow. With small drops it is almost white.

Halo - these are circles or arcs around the Sun and Moon that appear in upper-level ice clouds (most often in cirrostratus).

Crowns - light, slightly colored rings around the Sun and Moon, appearing in water and ice clouds of the upper and middle tiers, due to the diffraction of light.

Died on June 3. Parachute birthday

Basic Concepts

Unusual processes in the atmosphere

Halo around the Sun

Halo around the Moon and other types

False Sun

Rainbow

Polar Lights

Mirage

Brocken Ghost

St. Elmo's Fire

Designs in optics

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