The Gnessin universities listed are generally recognized. Russian Academy of Music named after Gnesins (RAM named after Gnesins)

Farajova Leila

Often we see in the sky unexplained phenomena. this work reveals the essence of the phenomena occurring in the earth's atmosphere.

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Municipal educational institution "Peschanovskaya secondary school"

VI regional scientific and practical conference

Optical phenomena in the atmosphere

6th grade Municipal educational institution "Peschanovskaya secondary school"

Supervisor:

Makovchuk Tatyana Gennadievna

Physics teacher

S. Peschanoye

2010

Introduction 3

Earth's atmosphere as an optical system 4

Types of optical phenomena 5

Conclusion 12

Literature 13

Appendix 14

Introduction

The purpose of this work is to consider optical atmospheric phenomena and their physical nature. The most accessible and at the same time the most colorful optical phenomena are atmospheric ones. Huge in scale, they are the product of the interaction of light and the earth's atmosphere.

On December 31, New Year's Eve, an unusual phenomenon could be observed in the southern part of the sky, not high above the horizon. There is a disk of the sun in the center and two more on the sides, and above them there is a rainbow glow. It was a very beautiful and mesmerizing sight. I immediately became interested in what it is, how it is formed, why and what other phenomena could occur in the atmosphere? This is unusual atmospheric phenomenon and formed the basis of my work.

The Earth's atmosphere as an optical system

Our planet is surrounded by a gaseous shell, which we call the atmosphere. Having its greatest density near the earth's surface and gradually thinning out as it rises, it reaches a thickness of more than a hundred kilometers. And this is not a frozen gaseous medium with homogeneous physical data. On the contrary, the Earth's atmosphere is in constant motion. Under the influence of various factors, its layers mix, change density, temperature, transparency, and move over long distances at different speeds.

For rays of light coming from the Sun or other celestial bodies, the earth's atmosphere is a kind of optical system with constantly changing parameters. Finding itself on their path, it reflects part of the light, scatters it, passes it through the entire thickness of the atmosphere, providing illumination of the earth's surface, under certain conditions, decomposes it into components and bends the course of rays, thereby causing various atmospheric phenomena. The most unusual colorful ones are sunsets, rainbows, northern lights, mirages, solar and lunar haloes and much more.

Types of optical phenomena

There are many types of optical phenomena. Let's look at some of them.

Halo

(from Greekχαλοσ - “circle”, “disk”; Also aura, halo, halo) is a phenomenon of refraction and reflection of light in ice crystals of upper clouds. They are light or rainbow circles around the Sun or Moon, separated from the luminary by a dark gap. Halos are often observed at the front of cyclones and can therefore serve as a sign of their approach. Sometimes you can see lunar halos.

Appearing in the air when water droplets freeze, ice crystals usually take one of three forms of six-sided regular prisms (Fig. 1 A): prisms in which the length is very large compared to their cross-section; These are the well-known ice needles that float in masses in the lowest layers of the atmosphere on frosty winter days.

A B C.

(Fig.1)

Falling freely in the air, such needles are positioned vertically with their long axis. The planes of these crystals, which whirl and gradually fall to the ground, are oriented parallel to the surface most of the time. At sunrise or sunset, the observer's line of sight can pass through this very plane, and each crystal can act as a miniature lens refracting sunlight.

In other types of prisms, the height is very small compared to the cross-section; then six-sided flat tablets are obtained (Fig. 1B.). Sometimes, finally, ice crystals take the form of a prism, the cross-section of which is a six-rayed star (Fig. 1 B.). Falling on ice crystals, a ray of light, depending on the type of crystal and its position relative to the ray, can directly or pass through it without refraction, or the rays must undergo not only refraction in them, but also a whole series of total internal reflections. In reality, it is very rare, of course, to observe a phenomenon, all parts of which would be equally bright and clearly visible: usually one or the other part of it is developed brighter and more characteristic, the rest are either observed very weakly or even absent.

An ordinary circle or small halo is a brilliant circle surrounding a star, its radius is about 22°. It is colored reddish on the inside, then yellow is faintly visible, then the color turns white and gradually merges with the general bluish tone of the sky.Spaceinside the circle appears relatively dark; the inner boundary of the circle is sharply outlined. This circle is formed by the refraction of light in ice needles flying in all sorts of positions in the air. The angle of minimum deviation of rays in an ice prism is approximately 22°, so all rays passing through the crystals should appear to the observer to be deviated from the light source by at least 22°; hence the darkness of the inner space. Red color, as the least refracted, will also seem to be the least deviated from the luminary; followed by yellow; the remaining rays, mixing with each other, give the impression of white color. Less common is a halo with an angular radius of 46°, located concentrically around a 22° halo. His inner side also has a reddish tint. The reason for this is also the refraction of light, which occurs in this case in ice needles facing the body at angles of 90°; This circle is usually paler than the small one, but the colors in it are more sharply separated. The width of the ring of such a halo exceeds 2.5 degrees. Both 46-degree and 22-degree halos tend to be brightest at the top and bottom of the ring. The rare 90-degree halo is a faintly luminous, almost colorless ring with general center with two other halos. If it is colored, it will have a red color on the outside of the ring. The mechanism by which this type of halo appears is not fully understood.

You can often observe the lunar halo.This is a fairly common sight and occurs if the sky is covered with high thin clouds with millions of tiny ice crystals. Each ice crystal acts as a miniature prism. Most crystals have the shape of elongated hexagons. Light enters through one front surface of such a crystal and exits through the opposite one with a refraction angle of 22º .

Watching street lamps in winter, you can see a halo generated by their light, under certain conditions, of course, namely in frosty air saturated with ice crystals or snowflakes. By the way, a halo from the Sun in the form of a large bright column can also appear during a snowfall. There are days in winter when snowflakes seem to float in the air, and sunlight stubbornly breaks through thin clouds. Against the background of the evening dawn, this pillar sometimes looks reddish - like the reflection of a distant fire. In the past, such a completely harmless phenomenon, as we see, terrified superstitious people.

Can see such a halo: a light, rainbow-colored ring around the Sun. This vertical circle occurs when there are many hexagonal ice crystals in the atmosphere that do not reflect, but refract Sun rays like a glass prism. In this case, most of the rays are naturally scattered and do not reach our eyes. But some part of them, having passed through these prisms in the air and refracted, reaches us, so we see a rainbow circle around the Sun. Its radius is about twenty-two degrees. It happens even more - forty-six degrees.

It is noticed that the halo circle is always brighter on the sides. This is because two halos intersect here - vertical and horizontal. And false suns are most often formed precisely at the intersection. Most favorable conditions for the appearance of false suns, they are formed when the Sun is low above the horizon and part of the vertical circle is no longer visible to us.

What crystals are involved in this “performance”?

The answer to the question was given by special experiments. It turned out that false Suns appear due to hexagonal ice crystals, shaped like... nails. They float vertically in the air, refracting light with their side faces.

The third "sun" appears when only one is visible above the real sun. top part halo circle. Sometimes it is a segment of an arc, sometimes a bright spot of indeterminate shape. Sometimes false suns are as bright as the Sun itself. Observing them, the ancient chroniclers wrote about three suns, severed fiery heads, etc.

In connection with this phenomenon, an interesting fact has been recorded in the history of mankind. In 1551, the German city of Magdeburg was besieged by the troops of the Spanish king Charles V. The defenders of the city held out steadfastly, and the siege lasted for more than a year. Finally, the irritated king gave the order to prepare for a decisive attack. But then the unprecedented happened: a few hours before the assault, three suns shone over the besieged city. The mortally frightened king decided that Magdeburg was protected by heaven and ordered the siege to be lifted.

Rainbow is an optical phenomenon that occurs in the atmosphere and has the appearance of a multi-colored arc in the firmament.

In the religious beliefs of ancient peoples, the rainbow was attributed to the role of a bridge between earth and sky. In Greco-Roman mythology, even a special goddess of the rainbow is known - Iris. The Greek scientists Anaximenes and Anaxagoras believed that rainbows were created by the reflection of the Sun in a dark cloud. Aristotle outlined ideas about the rainbow in a special section of his Meteorology. He believed that a rainbow occurs due to the reflection of light, but not just from the entire cloud, but from its drops.

In 1637 the famous French philosopher and the scientist Descartes gave a mathematical theory of the rainbow based on the refraction of light. Subsequently, this theory was supplemented by Newton based on his experiments on the decomposition of light into colors using a prism. Descartes' theory, supplemented by Newton, could not explain the simultaneous existence of several rainbows, their different widths, the obligatory absence of certain colors in the color stripes, or the influence of the size of cloud droplets on the appearance of the phenomenon. The exact theory of the rainbow, based on ideas about the diffraction of light, was given in 1836 by the English astronomer D. Airy. Considering the veil of rain as a spatial structure that ensures the occurrence of diffraction, Airy explained all the features of the rainbow. His theory has fully retained its significance for our time.

A rainbow is an optical phenomenon that appears in the atmosphere and looks like a multi-colored arc in the firmament. It is observed in cases when the sun's rays illuminate a curtain of rain located on the side of the sky opposite the Sun. The center of the rainbow arc is in the direction of a straight line passing through the solar disk (even if hidden from observation by clouds) and the eye of the observer, i.e. at a point opposite to the Sun. The arc of the rainbow is part of a circle described around this point with a radius of 42°30" (in angular dimension).

The arrangement of colors in the rainbow is interesting. It is always constant. The red color of the main rainbow is located on its upper edge, violet - on the lower edge. Between these extreme colors, the remaining colors follow each other in the same sequence as in the solar spectrum. In principle, a rainbow never contains all the colors of the spectrum. Most often, blue, dark blue and rich pure red colors are absent or weakly expressed. As the size of raindrops increases, the color stripes of the rainbow narrow, and the colors themselves become more saturated. The predominance of green tones in the phenomenon usually indicates a subsequent transition to good weather. The overall picture of the colors of the rainbow is blurred, since it is formed by an extended light source.

When artificially reproducing the phenomenon in the laboratory, it was possible to obtain up to 19 rainbows. Additional rainbows may be observed above the reservoir, non-concentrically located relative to each other. For one of them, the source of light is the Sun, for the other - its reflection from the water surface. Under these conditions, rainbows located “upside down” can also occur. At night, under moonlight and foggy weather, a white rainbow can be seen in the mountains and on the shores of the seas. This type of rainbow can also occur when fog is exposed to sunlight. It looks like a shiny white arc, painted yellowish and orange-red on the outside, and blue-violet on the inside. Rainbows are seen not only in the veil of rain. On a smaller scale it can be seen on drops of water near waterfalls, fountains and in sea ​​surf. In this case, not only the Sun and the Moon, but also a spotlight can serve as a light source.

Polar Lights - glow (luminescence) of the upper layers of the atmosphere of a planet with a magnetosphere due to its interaction with charged particles of the solar wind. 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. Intense flashes of radiance are often accompanied by sounds reminiscent of noise and crackling. Auroras cause strong changes in the ionosphere, which in turn affects radio communication conditions. In most cases, radio communications deteriorate significantly. There is strong interference, and sometimes a complete loss of reception.

Mirage - any of us has seen the simplest. For example, when you drive on a heated asphalt road, far ahead it looks like a water surface. And this kind of thing has not surprised anyone for a long time, because a mirage is nothing more than an atmospheric optical phenomenon, due to which images of objects appear in the visual zone that under normal conditions are hidden from observation. This happens because light is refracted when passing through layers of air of different densities. In this case, distant objects may appear to be raised or lowered relative to their actual position, and may also become distorted and acquire irregular, fantastic shapes.

Ghosts of Brocken - In some areas of the globe, when the shadow of an observer located on a hill at sunrise or sunset falls behind him on clouds located at a short distance, a striking effect is revealed: the shadow acquires colossal dimensions. This occurs due to the reflection and refraction of light by tiny water droplets in the fog. The described phenomenon is named after a peak in the Harz Mountains in Germany.

St. Elmo's Fire- luminous pale blue or purple brushes from 30 cm to 1 m or more in length, usually on the tops of masts or the ends of yards of ships at sea. Sometimes it seems that the entire rigging of the ship is covered with phosphorus and glows. St. Elmo's Fire sometimes appears on mountain peaks, as well as on the spiers and sharp corners of tall buildings. This phenomenon represents brush electric discharges at the ends of electrical conductors when the electric field strength in the atmosphere around them greatly increases.

Conclusion

The physical nature of light has interested people since time immemorial. But before I established myself modern look on the nature of light, and the light beam found its application in human life, many optical phenomena were identified, described, scientifically substantiated and experimentally confirmed, occurring everywhere in the Earth’s atmosphere, from the rainbow known to everyone, to complex, periodic mirages. But, despite this, the bizarre play of light has always attracted and attracts people. Neither the contemplation of a winter halo, nor a bright sunset, nor a wide, half-sky strip of northern lights, nor a modest lunar path on the surface of the water leaves anyone indifferent. A light beam passing through the atmosphere of our planet not only illuminates it, but also gives it a unique appearance, making it beautiful.

Of course, much more optical phenomena occur in the atmosphere of our planet, which are discussed in this work. Among them there are those that are well known to us and have been solved by scientists, as well as those that are still waiting for their discoverers. And we can only hope that, over time, we will witness more and more discoveries in the field of optical atmospheric phenomena, indicating the versatility of an ordinary light beam.

Literature

Bludov M.I. “Conversations on Physics, Part II” - M.: Education, 1985

Bulat V.L. “Optical phenomena in nature” - M.: Education, 1974.

Gershenzon E.M., Malov N.N., Mansurov A.N. "General Physics Course"- M.: Enlightenment, 1988

Korolev F.A. “Physics course” M., “Enlightenment” 1988

Myakishev G.Ya. Bukhovtsev B.B. “Physics 10 - M.: Education, 1987

Tarasov L.V. “Physics in Nature” - M.: Education, 1988.

Tarasov L.V. "Physics in Nature"- M.: Enlightenment, 1988

Trubnikov P.R. Pokusaev N.V. “Optics and atmosphere - St. Petersburg: Education, 2002.”

Shakhmaev N.M. Shodiev D.Sh. “Physics 11 - M.: Education, 1991.

Internet resources

Application

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.

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

Lake or lower mirages are the most common

mirage, a long-known natural phenomenon...

photograph, the ghost of Brocken, the shadow of a mountain seen against the background of evening clouds:

Halo is one of the most beautiful and unusual phenomena nature

We all know well that one of the main indicators of the value of the stones used in the manufacture jewelry, are their purity or transparency, as well as brightness and color stability. From ancient times, such expressions as “diamonds” have survived to this day. clean water", "pigeon blood rubies", "cornflower blue sapphires". However there is gems, the main highlight of which is the ability to exhibit unusual optical effects. Some of them can change color depending on the wavelength of the light source (Alexandrite), multi-beam “stars” appear on the surface of others, others shimmer like the irises of the eyes, and in others small inclusions of mica create a golden-silver “aventurine” shimmer. In addition, there are also such natural phenomena as iridescence (opals, moonstones, etc.), refraction of light on crystalline growth faces of minerals (astrophyllite, malachite, eudialyte, charoite), reflection from the surfaces of internal inclusions in transparent quartz (“hairworms”, rock crystal with sericite and chlorite) or chalcedony (fire agate containing hematite flakes), and much more. Even small bubbles of gas-liquid inclusions, arranged layer by layer in volcanic obsidian glass, give it iridescent gray hair.

Now all these phenomena are explained from the point of view of the science of the optical properties of minerals. However, over the years, humanity has attached numerous mystical properties to such stones precisely because of the unusual light effects. Thus, “eye” stones were supposed to protect their owners from the evil eye, aventurines were supposed to bring wealth, “asterics” were supposed to provide communication with other worlds….

ALEXANDRITE EFFECT OR COLOR CHANGE EFFECT
Alexandrite effect is a change in the visible color of a mineral depending on the nature of the lighting. Minerals with this effect show one color shade in natural light and a completely different one in artificial light. Most bright representative This phenomenon is alexandrite (a type of chrysoberyl), changing its color from yellowish, brownish, grayish and bluish-green (in daylight sunlight) to orangeish-red, brownish-red and purple-red (in artificial light). The greater the color change (reverse), the more valuable the stone.
The A.E. Fersman Mineralogical Museum (Moscow) houses the world's largest block of alexandrite. It weighs 5 kilograms and consists of 22 crystals, dark green during the day and bright red in the evening. The largest faceted alexandrite crystal weighing 66 carats is stored in Smithsonian Institution in Washington.
A similar effect is also known for some corundums, spinel, tourmaline, garnets, kyanite, and fluorite.

Photo: www.wiki.web.ru		Photo: www.wiki.web.ru

ASTERISM OR STAR EFFECT
Asterism (name from the Greek aster - star), or star effect, star effect is an optical phenomenon characteristic of some precious stones. The star effect occurs due to the reflection of light from internal inclusions in the stone. The number and direction of the rays depends on the type, location and orientation of the inclusions.
There are two types of asterism:
. diasterism, occurs when light passes through a stone;
. epiasterism occurs when light is reflected back (the light source is located directly above the polished surface), in this case only a 12-rayed star can be observed.
Rubies and sapphires processed in cabochon form are characterized by a 6-rayed star (mainly due to needle-shaped inclusions of rutile and/or hematite), but a 12-rayed star can also appear.
In crystals of diopside and enstatite, the reason for the appearance of a 4-rayed star is inclusions of magnetite. Although rare, 4- and 6-arm star grenades are found. The 6-rayed star can also be seen in rose quartz. There is a star-shaped spinel with a 6-rayed star, and much less often with a 4-rayed star. Its asterism is caused by orderly oriented inclusions of rutile, sillimanite and other minerals. But there are no more than a dozen 6-rayed star-shaped emeralds in the world.
Unfortunately, the popularity of “star stones” has led to a surge in the production of synthetic analogues, mainly rubies and sapphires. In synthetic stones, the stars are very bright, contrasting, the rays are very pronounced and clear. Natural corundum cut into cabochons with an artificially created star is becoming increasingly widespread.

IRISATION
Iridescence (from the Latin “iris” - the iris of the eye), an optical effect that appears in some minerals in the form of an internal rainbow-colored glow in bright light on evenly chipped stones and especially after polishing them. This effect is best seen in precious opal - opalescence .
Adularescence - a special case of iridescence, observed in the iridescent adularia, the actual “moonstone”. Adularia is a translucent to opaque variety of potassium feldspar with a wavy tint in white and blue tones. Currently, stores often sell imitations of moonstone under the guise of moonstone; their mass production has long been established in India and China on the basis of matte translucent tinted glass or plastic. A characteristic difference from natural ones is the absence of specific reflections during rotation; the imitation shines evenly at any angle.
Labradorescence - another special case of iridescence, which can be seen in labradorite (a mineral from the feldspar group) and spectrolite (a beautiful variety of Finnish labradorite), in the form of a rainbow play of colors on the faces and cleavage planes of crystals.

Photo: from the funds of the VO "World of Stone"

The atmosphere of our planet is a rather interesting optical system, the refractive index of which decreases with altitude due to a decrease in air density. Thus, the earth’s atmosphere can be considered as a “lens” of gigantic size, repeating the shape of the Earth and having a monotonically changing refractive index.

This circumstance leads to the emergence of a whole a number of optical phenomena in the atmosphere, caused by refraction (refraction) and reflection (reflection) of rays in it.

Let us consider some of the most significant optical phenomena in the atmosphere.

Atmospheric refraction

Atmospheric refraction- phenomenon curvature light rays as light passes through the atmosphere.

With height, the density of air (and therefore the refractive index) decreases. Let us imagine that the atmosphere consists of optically homogeneous horizontal layers, the refractive index of which varies from layer to layer (Fig. 299).

Rice. 299. Change in the refractive index in the Earth's atmosphere

When a light beam propagates in such a system, in accordance with the law of refraction, it will be “pressed” perpendicular to the layer boundary. But the density of the atmosphere does not decrease abruptly, but continuously, which leads to a smooth curvature and rotation of the beam by an angle α as it passes through the atmosphere.

As a result of atmospheric refraction, we see the Moon, Sun and other stars slightly higher than where they actually are.

For the same reason, the length of the day increases (in our latitudes by 10-12 minutes), and the disks of the Moon and Sun at the horizon shrink. Interestingly, the maximum angle of refraction is 35" (for objects near the horizon), which exceeds the apparent angular size of the Sun (32").

From this fact it follows: at the moment when we see that the lower edge of the star has touched the horizon line, in fact the solar disk is already below the horizon (Fig. 300).

Rice. 300. Atmospheric refraction of rays at sunset

Twinkling stars

Twinkling stars also related to astronomical refraction of light. It has long been noted that flickering is most noticeable in stars located near the horizon. Air currents in the atmosphere change the density of the air over time, which leads to the apparent flickering of the heavenly body. Astronauts in orbit do not observe any flickering.

Mirages

In hot desert or steppe regions and in polar regions, strong heating or cooling of air near the earth's surface leads to the appearance mirages: Thanks to the curvature of the rays, objects that are actually located far beyond the horizon become visible and appear close.

Sometimes this phenomenon is called terrestrial refraction. The occurrence of mirages is explained by the dependence of the refractive index of air on temperature. There are inferior and superior mirages.

Inferior Mirages can be seen on a hot summer day on a well-heated asphalt road: it seems to us that there are puddles ahead, which in fact are not there. IN in this case we take for “puddles” the mirror reflection of rays from non-uniformly heated layers of air located in close proximity from “hot” asphalt.

Upper mirages They are distinguished by significant diversity: in some cases they give a direct image (Fig. 301, a), in others - an inverted image (Fig. 301, b), they can be double and even triple. These features are associated with different dependences of air temperature and refractive index on height.

Rice. 301. Formation of mirages: a - direct mirage; b - reverse mirage

Rainbow

Atmospheric precipitation leads to the appearance of spectacular optical phenomena in the atmosphere. Thus, during the rain, an amazing and unforgettable sight is the formation rainbows, which is explained by the phenomenon of different refraction (dispersion) and reflection of solar rays on the smallest droplets in the atmosphere (Fig. 302).

Rice. 302. Formation of a Rainbow

In particularly successful cases, we can see several rainbows at once, the order of the colors in which is reversed.

The light ray involved in the formation of a rainbow undergoes two refractions and multiple reflections in each raindrop. In this case, somewhat simplifying the mechanism of rainbow formation, we can say that spherical raindrops play the role of a prism in Newton’s experiment on the decomposition of light into a spectrum.

Due to spatial symmetry, the rainbow is visible in the form of a semicircle with an opening angle of about 42°, while the observer (Fig. 303) should be between the Sun and raindrops, with his back to the Sun.

The variety of colors in the atmosphere is explained by patterns light scattering on particles of various sizes. Due to the fact that blue color scatters more than red, during the day, when the Sun is high above the horizon, we see the sky blue. For the same reason, near the horizon (at sunset or sunrise), the Sun becomes red and not as bright as at the zenith. The appearance of colored clouds is also associated with the scattering of light by particles of various sizes in the cloud.

Literature

Zhilko, V.V. Physics: textbook. allowance for 11th grade. general education institutions with Russian language training with a 12-year period of study (basic and advanced) / V.V. Zhilko, L.G. Markovich. - Minsk: Nar. Asveta, 2008. - pp. 334-337.

Volgograd Municipal Gymnasium No. 1

Examination paper

in physics on the topic:

"Optical phenomena in nature"

Completed

9th grade students "B"

Pokusaeva V.O.

Trubnikova M.V.

Plan

1. Introduction

a) What is optics?

b) Types of optics

c) The role of optics in the development of modern physics

2. Phenomena associated with the reflection of light

a) Object and its reflection

b) Dependence of the reflection coefficient on the angle of incidence of light

c) Safety glasses

e) Total reflection of light

e) Cylindrical light guide

g) Diamonds and gems

3. Phenomena associated with the refraction of light

b) Rainbow

4. Auroras

Introduction

What is optics?

The first ideas of ancient scientists about light were very naive. It was believed that special thin tentacles emerge from the eyes and visual impressions arise when they feel objects. At that time, optics was understood as the science of vision. This is the exact meaning of the word “optics”. In the Middle Ages, optics gradually transformed from the science of vision into the science of light, facilitated by the invention of lenses and the camera obscura. IN modern times optics is a branch of physics that studies the emission of light, its propagation in various media, and its interaction with matter. As for issues related to vision, the structure and functioning of the eye, they became a special scientific field called physiological optics.

Types of optics

When considering many optical phenomena, one can use the idea of ​​light rays - geometric lines along which light energy propagates. In this case, we talk about geometric (ray) optics.

Geometric optics is widely used in lighting engineering and in examining the actions of numerous instruments and devices - from magnifying glasses and glasses to the most complex optical microscopes and telescopes.

At the beginning of the 19th century, intensive research began on the previously discovered phenomena of interference, diffraction and polarization of light. These phenomena could not be explained within the framework of geometric optics; it was necessary to consider light in the form of transverse waves. This is how wave optics arose. Initially, it was believed that light is elastic waves in a certain medium (the world's ether), which supposedly fills all of the world's space.

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

Research carried out at the beginning of the 20th century showed that to explain some phenomena, for example the photoelectric effect, it is necessary to imagine a light beam in the form of a stream of peculiar particles - light quanta (photons). As early as 200 years ago, Isaac Newton held a similar point of view on the nature of light in his “theory of the effusion of light.” Now the concept of light quanta is studied by quantum optics.

The role of optics in the development of modern physics.

The role of optics in the development of modern physics is great. The emergence of two of the most important and revolutionary theories of the twentieth century (quantum mechanics and the theory of relativity) is significantly associated with optical research. Optical methods for analyzing matter at the molecular level have given rise to a special scientific field - molecular optics. It is closely related to optical spectroscopy, used in modern materials science, plasma research, and astrophysics. There are also electron and neutron optics; created electron microscope and a neutron mirror. Optical models of atomic nuclei have been developed.

Promoting development different directions modern physics, optics itself is currently experiencing a period of rapid development. The main impetus for this development was the invention of intense sources of coherent light - lasers. As a result, wave optics has risen to a higher level, corresponding to coherent optics. It is difficult to even list all the latest scientific and technical areas that are developing thanks to the advent of lasers. Among them are nonlinear optics, holography, radio optics, picosecond optics, adaptive optics and others. Radio optics arose at the intersection of radio engineering and optics; she studies optical methods for transmitting and processing information. These methods are usually combined with traditional electronic methods; As a result, a scientific and technical direction called optoelectronics emerged. The transmission of light signals through dielectric fibers is the subject of fiber optics. Using the achievements of nonlinear optics, it is possible to correct the wavefront of a light beam, which is distorted when light propagates in a particular medium, for example, in the atmosphere or in water. As a result, so-called adaptive optics arose and is being intensively developed. Closely related to it 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 wide practical use achievements of modern optics are a prerequisite scientific and technological progress. Optics opened the way to the microcosm for the human mind, and it also allowed it to penetrate the secrets of the stellar 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 coefficient reflections from 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 of the sun's rays from the windows of a house at different angles of incidence during the day, at sunset, and 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 most of 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 on 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 responsible for their 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

Mirage

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

Lower (“lake”) mirages appear above a very heated surface. Superior mirages, on the contrary, appear over a very cool surface, for example over 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 classified as one of these 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 in this case be bent 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 such “light guides”, which nature sometimes creates.

Rainbow

Rainbow is a beautiful celestial phenomenon that has always attracted human attention. In earlier 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; They also observe an even larger number of 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 sea bays, large 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 with sunlight 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 spectacular impression 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 additional unstable magnetic fields, so-called magnetic storms. During auroras, the atmosphere emits X-rays, which apparently result from the deceleration of electrons in the atmosphere.

Intense flashes of radiance are often accompanied by sounds reminiscent of noise and crackling. Auroras cause strong changes in the ionosphere, which in turn affects radio communication conditions. In most cases, radio communications deteriorate significantly. There is strong interference, and sometimes a complete loss of reception.

How auroras occur. The Earth is a huge magnet, the south pole of which is located near the north geographic pole, and the north pole is located near the south. Power lines magnetic field Lands called geomagnetic lines extend from the region adjacent to the Earth's north magnetic pole, covering Earth and enter it in the region of the south magnetic pole, forming a toroidal lattice around the Earth.

It has long been believed that the location of magnetic field lines is symmetrical relative to the earth's axis. Now it has become clear that the so-called “solar wind” - a stream of protons and electrons emitted by the Sun, strikes the geomagnetic shell of the Earth from a height of about 20,000 km, pulls it back, away from the Sun, forming a kind of magnetic “tail” on the Earth.

An electron or proton caught in the Earth's magnetic field moves in a spiral, as if winding around a geomagnetic line. Electrons and protons that enter the Earth's magnetic field from the solar wind are divided into two parts. Some of them immediately flow along magnetic lines of force into the polar regions of the Earth; others get inside the teroid and move inside it, as can be done according to the left-hand rule, along the closed curve ABC. These protons and electrons eventually also flow along geomagnetic lines to the region of the poles, where their increased concentration occurs. Protons and electrons produce ionization and excitation of atoms and molecules of gases. For this they have enough energy, 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. To ionize atoms you need: for hydrogen - 13.56 eV, for oxygen - 13.56 eV, for nitrogen - 124.47 eV, and for excitation even less.

Excited gas atoms give back the received energy in the form of light, similar to what happens in tubes with rarefied gas when currents are passed through them.

A spectral study shows that the green and red glow belongs to excited oxygen atoms, while 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. Another weak source of red light is hydrogen atoms, formed in the upper layers of the atmosphere from protons arriving from the Sun. Having captured an electron, such a proton turns into an excited hydrogen atom and emits red light.

Auroral flares usually occur a day or two after solar flares. This confirms the connection between these phenomena. Research using rockets has shown that in places of greater intensity of auroras there is more significant ionization of gases by electrons.

Recently, scientists have found that auroras are more intense near the coasts of oceans and seas.

But the scientific explanation of all phenomena associated with auroras encounters a number of difficulties. For example, the exact mechanism of acceleration of particles to the indicated energies is unknown, their trajectories in near-Earth space are not entirely clear, not everything quantitatively converges in the energy balance of ionization and excitation of particles, the mechanism of luminescence formation is not entirely clear various types, the origin of the sounds is unclear.

Literature:

5. “Encyclopedic Dictionary of a Young Physicist”, compiled by V. A. Chuyanov, Pedagogika Publishing House, Moscow, 1984.

6. “Schoolchildren’s Handbook on Physics”, compiled by - philological society “Slovo”, Moscow, 1995.

7. “Physics 11”, N. M. Shakhmaev, S. N. Shakhmaev, D. Sh. Shodiev, Prosveshchenie Publishing House, Moscow, 1991.

8. “Solving problems in physics”, V. A. Shevtsov, Nizhne-Volzhskoe book publishing house, Volgograd, 1999.

At school, the 6th grade is studying the topic “Optical phenomena in the atmosphere.” However, it is of interest not only to the inquisitive mind of children. Optical phenomena in the atmosphere, on the one hand, combine the rainbow, the change in color of the sky during sunrises and sunsets, which everyone has seen more than once. On the other hand, they include mysterious mirages, false Moons and Suns, impressive halos, which in the past terrified people. The mechanism of formation of some of them remains unclear even today, however general principle The basis by which optical phenomena “live” in nature has been well studied by modern physics.

Air envelope

The Earth's atmosphere is a shell consisting of a mixture of gases and extends approximately 100 km above sea level. The density of the air layer changes with distance from the earth: its greatest value is near the surface of the planet; it decreases with height. The atmosphere cannot be called a static formation. The layers of the gas shell are constantly moving and mixing. Their characteristics change: temperature, density, speed of movement, transparency. All these nuances affect the sun's rays rushing to the surface of the planet.

Optical system

The processes occurring in the atmosphere, as well as its composition, contribute to the absorption, refraction and reflection of light rays. Some of them reach their target - the earth's surface, while others are scattered or redirected back into outer space. As a result of the bending and reflection of light, the disintegration of some rays into a spectrum, and so on, various optical phenomena are formed in the atmosphere.

Video on the topic

Atmospheric optics

At a time when science was just emerging, people explained optical phenomena based on existing ideas about the structure of the Universe. The rainbow connected the human world with the divine; the appearance of two false Suns in the sky testified to approaching catastrophes. Today, most of the phenomena that frightened our distant ancestors have received a scientific explanation. Atmospheric optics studies such phenomena. This science describes optical phenomena in the atmosphere based on the laws of physics. She is able to explain why the sky is blue during the day and changes color during sunset and dawn, how a rainbow is formed and where mirages come from. Numerous studies and experiments today make it possible to understand such optical phenomena in nature as the appearance of luminous crosses, Fata Morgana, and rainbow halos.

Blue sky

The color of the sky is so familiar that we rarely think about why it is that way. Nevertheless, physicists know the answer well. Newton proved that a ray of light certain conditions decomposed into a spectrum. When the atmosphere passes through, the part corresponding to the blue color is scattered better. The red region of visible radiation is characterized by a longer wavelength and is 16 times inferior to the violet region in terms of scattering.

At the same time, we see the sky not violet, but blue. The reason for this lies in the peculiarities of the structure of the retina and the ratio of spectral regions in sunlight. Our eyes are more sensitive to blue, and the violet part of the light's spectrum is less intense than blue.

Scarlet sunset

When people figured out what the atmosphere was, optical phenomena ceased to be evidence or an omen for them terrible events. However, the scientific approach does not interfere with receiving aesthetic pleasure from colorful sunsets and gentle sunrises. Bright red and orange colors together with pink and blue, they gradually give way to night darkness or morning light. It is impossible to observe two identical sunrises or sunsets. And the reason for this lies in the same mobility of atmospheric layers and changes in weather conditions.

During sunsets and sunrises, the sun's rays travel a longer distance to the surface than during the day. As a result, scattered violet, blue and green go to the sides, and direct light turns red and orange. Clouds, dust or ice particles suspended in the air contribute to the picture of sunset and dawn. Light is refracted as it passes through them, and colors the sky in a variety of shades. On the horizon opposite to the Sun, you can often observe the so-called Belt of Venus - a pink stripe separating the dark night sky and the blue daytime sky. The beautiful optical phenomenon, named after the Roman goddess of love, is visible before dawn and after sunset.

Rainbow Bridge

Perhaps no other light phenomena in the atmosphere evokes as many mythological stories and fairy-tale images as are associated with the rainbow. An arc or circle consisting of seven colors is known to everyone since childhood. The beautiful atmospheric phenomenon that occurs during rain, when the sun's rays pass through the drops, fascinates even those who have thoroughly studied its nature.

And the physics of the rainbow is no secret to anyone today. sunlight, when refracted by drops of rain or fog, it splits. As a result, the observer sees seven colors of the spectrum, from red to violet. The boundaries between them are impossible to determine. The colors smoothly transition into each other through several shades.

When observing a rainbow, the sun is always located behind a person's back. The center of Iris’s smile (as the ancient Greeks called the rainbow) is located on a line passing through the observer and the daylight. Usually a rainbow appears in the form of a semicircle. Its size and shape depend on the position of the Sun and the point at which the observer is located. The higher the star is above the horizon, the lower the circumference of the possible appearance of a rainbow falls. When the Sun passes 42º above the horizon, an observer on the Earth's surface cannot see a rainbow. The higher above sea level a person is located who wants to admire Iris’s smile, the more likely it is that he will see not an arc, but a circle.

Double, narrow and wide rainbow

Often, along with the main one, you can see the so-called side rainbow. If the first is formed as a result of a single reflection of light, then the second is the result of a double reflection. In addition, the main rainbow is distinguished by a certain order of colors: red is located on the outer side, and violet is located on the inner side, which is closer to the surface of the Earth. The side “bridge” is a spectrum that is the opposite in sequence: violet is at the top. This happens because during double reflection from a raindrop, the rays come out at different angles.

Rainbows vary in color intensity and width. The brightest and rather narrow ones appear after a summer thunderstorm. The large drops characteristic of such rain give rise to a clearly visible rainbow with clearly distinguishable colors. Small droplets produce a more diffuse and less noticeable rainbow.

Optical phenomena in the atmosphere: aurora

One of the most beautiful atmospheric optical phenomena is the aurora. It is typical for all planets with a magnetosphere. On Earth, auroras are observed at high latitudes of both hemispheres, in zones surrounding the planet's magnetic poles. Most often you can see a greenish or blue-green glow, sometimes supplemented at the edges with flashes of red and pink. The intense aurora is shaped like ribbons or folds of fabric, which turn into spots when they fade. The stripes, several hundred kilometers high, stand out clearly along the lower edge against the dark sky. The upper boundary of the aurora is lost in the heights.

These beautiful optical phenomena in the atmosphere still keep their secrets from people: the mechanism of occurrence of some types of glow and the reason for the crackling noise that occurs during sharp flashes have not been fully studied. However big picture The formation of auroras is known today. The skies above the north and south poles are adorned with a greenish-pink glow as charged particles from the solar wind collide with atoms in the Earth's upper atmosphere. As a result of interaction, the latter receive additional energy and emit it in the form of light.

Halo

The Sun and Moon often appear before us surrounded by a halo-like glow. This halo is a clearly visible ring around the light source. In the atmosphere, it most often forms due to the smallest particles of ice that make up cirrus clouds high above the Earth. Depending on the shape and size of the crystals, the characteristics of the phenomenon change. Often the halo takes on the appearance of a rainbow circle as a result of the decomposition of the light beam into a spectrum.

An interesting type of phenomenon is called parhelia. As a result of the refraction of light in ice crystals at the level of the Sun, two light spots are formed, reminiscent of the daylight. In historical chronicles you can find descriptions of this phenomenon. In the past, it was often considered a harbinger of terrible events.

Mirage

Mirages are also optical phenomena in the atmosphere. They arise as a result of the refraction of light at the boundary between layers of air that differ significantly in density. The literature describes many cases when a traveler in the desert saw oases or even cities and castles that could not be nearby. Most often these are “lower” mirages. They appear over a flat surface (desert, asphalt) and represent a reflected image of the sky, which appears to the observer as a body of water.

So-called superior mirages are less common. They form above a cold surface. Superior mirages can be straight or inverted, sometimes combining both positions. The most famous representative of these optical phenomena is Fata Morgana. This is a complex mirage that combines several types of reflections at once. Really existing objects appear before the observer, repeatedly reflected and moved.

Atmospheric electricity

Electrical and optical phenomena in the atmosphere are often mentioned together, although the reasons for their occurrence are different. Cloud polarization and lightning formation are associated with processes occurring in the troposphere and ionosphere. Giant spark discharges usually form during a thunderstorm. Lightning occurs inside clouds and can strike the ground. They are a threat to human life, and this is one of the reasons for scientific interest in such phenomena. Some properties of lightning still remain a mystery to researchers. Today the cause of ball lightning is unknown. As with some aspects of the theory of auroras and mirages, electrical phenomena continue to intrigue scientists.

Optical phenomena in the atmosphere, briefly described in the article, are becoming more and more understandable to physicists every day. At the same time, they, like lightning, never cease to amaze people with their beauty, mystery and sometimes grandeur.