What are light phenomena in physics. Unique light phenomena. Phenomenon in life
You've probably seen a rainbow and perhaps know what a mirage is on a hot road. Some of us have been luckier and have seen natural phenomena such as the northern lights, white or inverted rainbows and star trails with our own eyes.
In this post, I have selected a little more than a dozen natural phenomena that appear as a result of refraction or other action of light. In short, these are light phenomena that make for stunning photographs and unforgettable experiences. 
1. Rainbow wall
A rare atmospheric phenomenon, also known as a “fire rainbow,” occurs when the horizontal rays of the rising or setting sun are refracted through horizontal ice crystals in clouds. The result is a kind of wall painted in different colors of the rainbow. The photo was taken in the skies of Washington in 2006. 
2. Halo
The sun's rays are reflected from ice crystals located at an angle of 22° relative to the Sun in high-altitude clouds. Different positions of ice crystals can cause halo modifications. On frosty days, a “diamond dust” effect can be observed, in which case the sun’s rays are repeatedly reflected from ice crystals. 
3. Airplane contrails
Aircraft exhaust and eddy currents at high altitudes turn ice particles into water. The long white streaks high in the sky are nothing more than suspended water droplets. 
4. Crepuscular rays
The setting sun's rays passing through gaps in the clouds form clearly visible individual beams of sunlight. Very often such sun rays can be seen in various science fiction films. This photo was taken in one of Utah's national parks. 
5. Northern Lights
The Northern Lights are nothing more than a collision in the upper layers of the atmosphere of solar rays with charged particles of gases from the Earth's magnetic field. 
6. Star trails
A visual demonstration of the rotation of the Earth. This phenomenon is invisible to the naked eye. To get such a photograph, you need to set the camera to a long shutter speed. In the picture, only the only North Star, located almost above the Earth’s axis, remains almost motionless. 
7. White rainbow
Photo taken on the Golden Gate Bridge in San Francisco. The small size of airy water droplets makes it impossible to decompose the sun's rays into spectra of colors, so the rainbow is only white. 
8. Buddha Light
This photo was taken in China. The phenomenon is similar to the “Ghost of Brocken”. The sun's rays are reflected from atmospheric droplets of water over the sea, the shadow in the middle of the rainbow circle of reflected rays is the shadow of an airplane. 
9. Inverted Rainbow
Such an unusual rainbow also appears as a result of the refraction of sunlight through ice crystals located only in certain parts of the clouds. 
10. Mirage
A very common atmospheric phenomenon. It can be observed not only in the desert, but also on the road in the sultry heat. This phenomenon is formed as a result of the refraction of sunlight through a “lens” formed by layers of colder (near the surface of the earth) and warmer (located above) air. This kind of lens reflects objects located above the horizon, in this case the sky. Photo taken in Thuringia (Germany). 
11. Iridescent clouds
The rays of the setting sun at right angles “bump into” the water droplets of the clouds. As a result of diffraction (the bending of water droplets by the sun's rays) and the interference of sun rays (the decomposition of sun rays into spectra), the cloud figure is filled with a gradient fill, as in Photoshop. 
12. Rocket exhaust trail
The trail of a Minotaur missile fired by the US Air Force in California. Air currents blowing at different altitudes at different speeds cause distortion in the wake of rocket exhaust. Atmospheric water droplets from melted ice crystals also cause sunlight to split into different colors of the rainbow. 
13. Ghost of Brocken, Germany
This phenomenon occurs on a foggy morning. The rainbow solar disk appears opposite the sun as a result of the reflection of the sun's rays from droplets of water in the fog. The curious triangular shadow breaking the iridescent disk of reflected sunlight is nothing more than a projection of the upper surface of the clouds. 
14. Zodiacal light
Zodiacal light often masks moonlight and artificial city light. On a quiet, moonless night in nature, the likelihood that you will see the zodiacal light is quite high. This phenomenon is observed as a result of the reflection of solar rays from particles of cosmic dust surrounding the Earth.
bird phenomena in nature.
Phenomena associated with the reflection of light. The object and its reflection.
The fact that the landscape reflected in the 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.
Rainbow. 
Rainbow is a beautiful celestial phenomenon that has always attracted human attention.
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.
A rainbow is observed in the direction opposite to the Sun, against the background of rain clouds or rain. A 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 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.
Most often we see one rainbow. There are often cases when two rainbow stripes appear simultaneously in the sky, located one after the other; They also observe an even larger number of celestial arcs - three, four and even five at the same time.
Polar lights.
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 spots.
Based on the brightness of the aurora, they are divided into four classes, differing from each other by an order of magnitude. Class 1 includes auroras that are barely noticeable and approximately equal in brightness to the Milky Way, while class 4 auroras illuminate the Earth as brightly as the full Moon.
Light beam in geometric optics, a line along which light energy is transferred. Less clearly, but more clearly, a beam of light of small transverse size can be called a light ray.
The concept of a light ray is a cornerstone approximation of geometric optics. This definition implies that the direction of the flow of radiant energy (path of the light beam) does not depend on the transverse dimensions of the light beam. Because light is a wave phenomenon, diffraction occurs, and as a result, a narrow beam of light does not travel in any one direction, but has a finite angular distribution.
Law of rectilinear propagation of light: In a transparent, homogeneous medium, light travels in straight lines.
In connection with the law of rectilinear propagation of light, the concept of a light ray appeared, which has a geometric meaning as a line along which light propagates. Light beams of finite width have a real physical meaning. The light beam can be considered as the axis of the light beam. Since light, like any radiation, transfers energy, we can say that a light beam indicates the direction of energy transfer by the light beam. Also, the law of rectilinear propagation of light allows us to explain how solar and lunar eclipses occur (The figure shows a solar eclipse. During a lunar eclipse, the Moon and Earth “change” places).
Light dispersion(decomposition of light) is the phenomenon of the dependence of the absolute refractive index of a substance on the wavelength (or frequency) of light (frequency dispersion), or, which is the same, the dependence of the phase speed of light in a substance on the wavelength (or frequency). It was discovered experimentally by Newton around 1672, although theoretically quite well explained much later.
Color- a qualitative subjective characteristic of electromagnetic radiation in the optical range, determined on the basis of the emerging physiological visual sensation and depending on a number of physical, physiological and psychological factors.
The sensation of color occurs in the brain through excitation and inhibition of color-sensitive cells - receptors in the retina of a person or other animal, cones. It is believed (although no one has proven it to date) that in humans and primates there are three types of cones differing in spectral sensitivity - conventionally “red”, conventionally “green” and conventionally “blue”. The light sensitivity of cones is low, so sufficient illumination or brightness is necessary for good color perception. The central parts of the retina are richest in color receptors.
Each color sensation in a person can be represented as the sum of the sensations of these three colors (the so-called “three-component theory of color vision”). It has been established that reptiles, birds and some fish have a wider range of perceived optical radiation. They perceive near ultraviolet (300-380 nm), blue, green and red parts of the spectrum. When the brightness necessary for color perception is reached, the most highly sensitive receptors of twilight vision - the rods - are automatically turned off.
Reflection- the phenomenon of partial or complete return of waves (electromagnetic) reaching the interface between two media (obstacles) into the medium from which they approach this boundary.
Law of Light Reflection- establishes a change in the direction of travel of a light ray as a result of a meeting with a reflecting (mirror) surface: the incident and reflected rays lie in the same plane with the normal to the reflecting surface at the point of incidence, and this normal divides the angle between the rays into two equal parts. The widely used but less precise formulation “the angle of reflection is equal to the angle of incidence” does not indicate the exact direction of reflection of the beam.
A universal concept in physics is the speed of light. c. Its value in a vacuum represents not only the maximum speed of propagation of electromagnetic oscillations of any frequency, but also, in general, the maximum speed of propagation of any impact on material objects. When light propagates in various media, the speed of light v decreases: v=c/n, Where n is the refractive index of a medium, characterizing its optical properties and depending on the frequency of light n = n(v).
Refraction- a change in the direction of propagation of waves of electromagnetic radiation that occurs at the interface between two media transparent to these waves or in the thickness of a medium with continuously changing properties.
The refraction of light at the boundary of two media gives a paradoxical visual effect: straight objects crossing the interface in a denser medium appear to form a larger angle with the normal to the interface (that is, refracted “upwards”); while a ray entering a denser medium propagates in it at a smaller angle to the normal (that is, it is refracted “down”). The same optical effect leads to errors in visually determining the depth of a reservoir, which always seems smaller than it actually is.
The refraction of light in the Earth's atmosphere leads to the fact that we observe the sunrise a little earlier, and the sunset a little longer than would be the case in the absence of an atmosphere. For the same reason, near the horizon, the disk of the Sun looks noticeably flattened along the vertical.
Snell's Law refraction of light describes the refraction of light at the boundary of two media. It is also applicable to describe the refraction of waves of a different nature, such as sound.
The angle of incidence of light on a surface is related to the angle of refraction by the relation
Here:
n 1- refractive index of the medium from which light falls on the interface;
A 1- angle of incidence of light - the angle between the beam incident on the surface and the normal to the surface;
n 2- refractive index of the medium into which light enters after passing the interface;
A 2- angle of refraction of light - the angle between the ray passing through the surface and the normal to the surface.
Lens- a part made of an optically transparent homogeneous material, limited by two polished refractive surfaces of rotation, for example, spherical or flat and spherical. Currently, “aspherical lenses”, the surface shape of which differs from a sphere, are increasingly being used. Optical materials such as glass, optical glass, optically transparent plastics and other materials are commonly used as lens materials.
Depending on the shape, a distinction is made between converging (positive) and diverging (negative) lenses. The group of collecting lenses usually includes lenses whose middle is thicker than their edges, and the group of diverging lenses includes lenses whose edges are thicker than the middle. It should be noted that this is only true if the refractive index of the lens material is greater than that of the surrounding medium. If the refractive index of the lens is lower, the situation will be reversed. For example, an air bubble in water is a biconvex diverging lens.
Lenses are typically characterized by their optical power (measured in diopters), or focal length.
If light from a very distant source, the rays of which can be imagined as coming in a parallel beam, falls on the lens, then when leaving it the rays will refract at a large angle, and point F, the point of intersection of these rays, will move on the optical axis closer to the lens. Under these conditions, the point of intersection of the rays emerging from the lens is called the focus F, and the distance from the center of the lens to the focus is focal length.
Optical power- a quantity characterizing the refractive power of axisymmetric lenses and centered optical systems made from such lenses. The optical power is measured in dioptres(in the SI system) and is inversely proportional to the focal length:
Construction of images produced by a thin lens.
Let us consider a ray SA of an arbitrary direction incident on a lens at point A. Let us construct a line of its propagation after refraction in the lens. To do this, we construct a ray OB parallel to SA and passing through the optical center O of the lens. According to the first property of the lens, the ray OB will not change its direction and will intersect the focal plane at point B. According to the second property of the lens, the parallel ray SA after refraction must intersect the focal plane at the same point. Thus, after passing through the lens, the ray SA will follow the path AB.
Other beams, such as the SPQ beam, can be constructed in a similar way.
Let us denote the distance SO from the lens to the light source by u, the distance OD from the lens to the point of focusing of the rays by v, and the focal length OF by f. Let us derive a formula connecting these quantities.
Let's consider two pairs of similar triangles: 1) SOA and OFB; 2) DOA and DFB. Let's write down the proportions
Dividing the first proportion by the second, we get
After dividing both sides of the expression by v and rearranging the terms, we arrive at the final formula
Photometry. Luminous intensity and illumination.
Photometry is a scientific discipline common to all branches of applied optics, on the basis of which quantitative measurements of the energy characteristics of the radiation field are made.
The power of light is the quantitative value of the radiation flux per unit solid angle of its propagation limit. In other words, this is the amount of light (in lumens) per 1 steradian.
The solid angle must be chosen in such a way that the flow limited by it can be considered the most uniform. Then a unit of solid angle in this direction from the source will contain a luminous intensity numerically equal to the luminous flux
SI unit: candela (cd) = lumen (lm) / steradian (sr)
Illumination- a physical quantity numerically equal to the luminous flux incident on a unit surface:
The SI unit of illumination is the lux (1 lux = 1 lumen/sq. meter).
Light flow- a physical quantity characterizing the “amount” of light energy in the corresponding radiation flux. In other words, this is the power of such radiation that is perceptible to the normal human eye (F).
Eye- a sensory organ of humans and animals that has the ability to perceive electromagnetic radiation in the light wavelength range and provides the function of vision. 90 percent of information from the outside world comes through the eye.
Myopic is an eye in which the focus, when the eye muscle is calm, lies inside the eye. Myopia can be caused by a greater distance between the retina and the lens compared to a normal eye. If an object is located at a distance of 25 cm from a myopic eye, then the image of the object will not be on the retina, but closer to the lens, in front of the retina. In order for the image to appear on the retina, you need to bring the object closer to the eye. Therefore, in a myopic eye, the distance of best vision is less than 25 cm. A farsighted eye is an eye whose focus, when the eye muscle is at rest, lies behind the retina. Farsightedness can also be caused by the fact that the retina is located closer to the lens compared to a normal eye and the image of an object is obtained behind the retina of such an eye. If an object is removed from the eye, the image will fall on the retina, hence the name of this defect - farsightedness.
Myopia and farsightedness are corrected by using lenses. The invention of glasses was a great boon for people with visual impairments.
In a nearsighted eye, the image is obtained inside the eye in front of the retina. In order for it to move to the retina, the optical power of the refractive system of the eye must be reduced. For this purpose, a diverging lens is used.
The optical power of the farsighted eye system, on the contrary, must be strengthened in order for the image to fall on the retina. For this purpose, a collecting lens is used.
Optical instruments.
Optical instruments- devices in which radiation from any region of the spectrum (ultraviolet, visible, infrared) is transformed (transmitted, reflected, refracted, polarized). They can increase, decrease, improve (in rare cases worsen) the quality of the image, and make it possible to see the desired object indirectly.
The term "Optical devices" is a special case of the more general concept of optical systems, which also includes biological organs capable of converting light waves.
Spotting scope- an optical device for observing distant objects, consists of a lens that creates a real image of objects, and an eyepiece for magnifying this image.
Microscope- a device designed to obtain magnified images, as well as measure objects or structural details invisible to the naked eye. It is a collection of lenses.
Magnifier- an optical system consisting of a lens or several lenses, designed to magnify and observe small objects located at a finite distance.
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The nature of light. Interference and diffraction of light. Diffraction grating. X-ray diffraction analysis and its use. Natural and polarized light. Optically active substances. Polarimetry. Study of biological systems in polarized light. Dispersion of light. Absorption and scattering of light. Scattering of light in the atmosphere.
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Optics (from the Greek word optikos - visual) is a branch of physics that studies the nature of light, the laws of light phenomena and the processes of interaction of light with matter.
Over the past three centuries, the understanding of the nature of light has undergone a very significant change. At the end of the 17th century. Two fundamentally different theories about the nature of light have emerged: corpuscular theory, developed by Newton, and wave theory, developed by Huygens. According to the corpuscular theory, light is a flow of material particles (corpuscle), flying at high speed from a light source.
According to the wave theory, light is a wave emanating from a light source and propagating at high speed in the “world ether” - a stationary elastic medium that continuously fills the entire Universe. Thus, the wave theory viewed light as mechanical waves propagating in a special medium (like sound waves in air).
Until the end of the 18th century. the overwhelming majority of physicists preferred Newton's corpuscular theory. At the beginning of the 19th century, thanks to research cabin boy And Fresnel wave theory was significantly developed and improved. The wave theory successfully explained almost all light phenomena known at that time, including interference, diffraction and polarization of light, due to which this theory received universal acceptance, and Newton's corpuscular theory was rejected.
The weak point of the wave theory was the hypothetical “world ether”, the reality of whose existence remained very doubtful (in 1881, the American physicist Michelson experimentally proved that the world ether does not exist). In the 60s of the 19th century, when Maxwell developed the theory of a unified electromagnetic field, the need for the “world ether” as a special carrier of light waves disappeared: it turned out that light is electromagnetic waves and, therefore, their carrier is the electromagnetic field.
Visible Light corresponds to electromagnetic waves with a length of 0.77 to 0.38 microns, created by vibrations of the charges that make up atoms and molecules. Thus the wave theory of the nature of light evolved into electromagnetnew theory of light.
The idea of the wave (electromagnetic) nature of light remained unshakable until the end of the 19th century. However, by this time quite extensive material had accumulated that was not consistent with this idea and even contradicted it.
The study of data on the luminescence spectra of chemical elements, on the distribution of energy in the spectrum of thermal radiation of a black body, on the photoelectric effect and some other phenomena led to the need to assume that the emission and absorption of electromagnetic energy is discrete(intermittent) nature, i.e. light is emitted and absorbed not continuously (as followed from the wave theory), but portions (quanta).
Based on this assumption, the German physicist Planck in 1900 he created the quantum theory of electromagnetic processes, and Einstein developed in 1905 quantum theory of light, according to which light is a stream light particles- photons. However, photons differ significantly (qualitatively) from ordinary material particles: all photons move at a speed equal to the speed of light, while possessing ultimate mass (“rest mass” of the photon is zero).
An important role in the further development of the quantum theory of light was played by theoretical studies carried out by Borom, Schrödinger, Dirac, Feynman, Focom etc. According to modern views, light- complex electromagnetic process with both wave and corpuscular propertiesyou.
In some phenomena (interference, diffraction, polarization of light) the wave properties of light are revealed; these phenomena are described by wave theory. In other phenomena (photoelectric effect, luminescence, atomic and molecular spectra) the corpuscular properties of light are revealed; such phenomena are described by quantum theory.
Thus, wave (electromagnetic) and corpuscular (quantum) theories do not reject, but complement each other, thereby reflecting dual nature of the properties of light. Here we encounter a clear example of the dialectical unity of opposites: light is both a wave and a particle. It is appropriate to emphasize that such dualism is inherent not only to light, but also to microparticles of substances.
Modern physics strives to create single a theory about the nature of light, reflecting the dual corpuscular-wave nature of light; the development of such a unified theory has not yet been completed.
Light interference is the phenomenon of amplification or weakening of vibrations that occurs as a result of the addition of two or more waves converging at a certain point in space. A necessary condition for the interference of waves is their coherence: the equality of their frequencies and a constant phase difference over time. This condition satisfy monochromatic light waves (from the Greek (monos) - one, (chroma) - color, i.e. monochromatic light corresponds to any one wavelength). If this condition is met, interference of other waves (for example, sound) can also be observed.
For light waves, as well as for any others, the principle of superposition is valid. Since light has an electromagnetic nature, the application of this principle means that the resulting electric (magnetic) field strength of two light waves passing through one point is equal to the vector sum of the electric (magnetic) field strengths of each wave separately.
In the particular case when the strengths of the component fields are equal but opposite in direction, the strength of the resulting field will be zero (the light is extinguished by the light). If they are directed in one direction, maximum light amplification occurs.
The result of interference is an interference pattern - a time-stable distribution in space of interference maxima and minima (for example, alternating dark and light stripes on the screen; in nature, the rainbow coloring of the wings of insects and birds, soap bubbles, an oil film on water, etc.).
A special case of the interference pattern are the so-called Newton rings (Figure 4.1)
Figure 4.1
They are observed in a system formed by a plane-parallel plate and a plano-convex lens with a large radius of curvature in contact with it.
The result of the interference of two light waves (in the same medium) depends on the path difference Δl=l 1 -l 2 (Figure 4.2).
Figure 4.2
If the difference in the path of the rays contains an even number of half-waves, i.e. If
(4.1.1)
then at point A there will be a maximum of light on the screen (λ is the wavelength, S 1 and S 2 are monochromatic light sources, n = 0,1,2,3,...). If the path difference of the rays contains an odd number of half-waves, i.e. If
(4.1.2)
then at point A there will be a minimum of light. The interference pattern created by two coherent light sources on the screen is an alternation of dark and light stripes.
The interference pattern is very sensitive to the magnitude of the path difference between the interfering waves. Based on this interferometer device a device used to determine small lengths, angles, refractive index of a medium, and light wavelengths.
Diffraction is the deflection of light from linear propagation near an obstacle (light bending around an obstacle). So, for example, if another screen B with a hole is placed between the light source S and screen A, on screen A you can observe a diffraction pattern consisting of alternating light and dark rings and capturing the area of the geometric shadow (especially noticeable when the size of the hole is much smaller than the distance between the screens).
Figure 4.3
When white (non-monochromatic light) is used, the diffraction pattern becomes rainbow-colored.
The phenomenon of diffraction is explained using the Huygens–Fresnel principle. According to this principle, each point of the wave surface reaching the hole becomes a secondary light source. These sources are coherent, so the light rays emanating from them will interfere with each other. Depending on the magnitude of the path difference, maximums and minimums of illumination will appear on screen A. In laboratory practice, the diffraction pattern is usually obtained from narrow luminous slits. A set of a large number of parallel narrow slits transparent to light, separated by opaque spaces, is called diffraction grating. Diffraction gratings are made by applying fine lines to the surface of a glass plate (transparent grating) or a metal mirror (reflective). The sum of the slit width a and the gap b between the slits is called the period or lattice constant: d = a + b. Diffraction gratings produce a clear diffraction pattern and are used to determine wavelength, as well as in spectral analysis to decompose light into a spectrum and draw conclusions about the chemical composition of a substance. Diffraction patterns often occur in nature. For example, colored rings surrounding a light source when the air is saturated with water droplets (fog) or dust are the result of light diffraction on these particles. Diffraction explains the color of mother-of-pearl and the iridescent color of the eyes of many insects, whose eyes are a kind of diffraction gratings.
In chemistry, X-ray diffraction analysis, a method for studying the structure of a substance by the spatial distribution and intensity of X-ray radiation scattered on the analyzed object, has become widely used. It is based on the interaction of X-ray radiation with electrons of a substance, which results in X-ray diffraction. The diffraction pattern depends on the wavelength of the x-rays used and the structure of the object. To study atomic structure, radiation with a wavelength on the order of the size of atoms is used. X-ray diffraction analysis methods are used to study metals, alloys, minerals, inorganic and organic compounds, polymers, amorphous materials, liquids and gases, protein molecules, nucleic acids, etc. It is most successfully used to establish the atomic structure of crystalline bodies. This is due to the fact that crystals have a strictly periodic structure and represent a diffraction grating for x-rays created by nature itself.
Light represents the total electromagnetic radiation of many atoms. As is known, an electromagnetic wave can be represented in the form of oscillations of two mutually perpendicular intensities of electric E and magnetic H. Since the electromagnetic wave is transverse, both vectors oscillate in planes perpendicular to the velocity vector - the direction of propagation of the beam. An electromagnetic wave in which only one of these vectors oscillates is impossible. The electric field in which E changes inevitably generates a magnetic field in which H changes according to the same law, and vice versa. The phenomena of polarization are considered relative to the intensity vector E, but one should remember about the obligatory existence of the intensity vector H perpendicular to it. The plane in which the electric field intensity vector oscillates is called the oscillation plane. The plane in which the magnetic field strength vector oscillates is called the plane of polarization.
Natural light from this point of view can be schematically represented as follows (Figure 4.4):
Figure 4.4
The uniform arrangement of vectors E is due to the large number of atomic emitters. This kind of light is called unpolarized. In such light waves, the vectors have different orientations of vibrations, and all orientations are equally probable. If, due to the influence of external influences on light or internal features of the light source, the preferred, most probable direction of oscillation appears, then such light is called partially polarized(Figure 4.5) .
Figure 4.5
Using special devices, it is possible to select a beam from a beam of natural light in which the oscillations of vector E will occur in one specific plane (Figure 4.6)
Figure 4.6
Such light will be completely polarized. Unlike natural light, polarized light is characterized in addition to intensity and wavelength by the position of the plane of polarization. The human eye does not distinguish between natural and polarized light. In practice, polarized light is usually produced by passing natural light through crystals, which are known to be anisotropic (physical properties dependent on direction in the crystal). Polarized light is widely used in chemical and biological research. For example, some substances, called optically active, rotate the plane of polarization of polarized light passing through them. Moreover, the angle of rotation depends on the thickness of the layer of substance. Thus, it is possible to determine the concentration of substances in a solution, which underlies the method of studying substances - polarimetry. Using optical polarimeters, the amount of rotation of the plane of polarization of light is determined when it passes through optically active media (solids or solutions). Polarimetry is widely used in analytical chemistry to quickly measure the concentration of optically active substances for the identification of essential oils and in other studies. Almost all biologically functional molecules are optically active.
An important optical characteristic of the medium is absolute refractive index n (or simply refractive index). It shows how many times the speed of light in a given medium is less than the speed of light in a vacuum
(4.1.3)
The value of the refractive index of a medium is mainly determined by the properties of this medium. However, to some extent it also depends on the wavelength (frequency) of the light. Therefore, the same medium refracts light rays of different wavelengths differently. The dependence of the refractive index of a medium on the wavelength of light is called light dispersion (from the Latin dispersio - scattering).
The dispersion is called normal if the refractive index increases with decreasing light wave, otherwise it is anomalous. Thanks to dispersion, a beam of white light passing through a refractive medium is split into various monochromatic beams (red, orange, yellow, green, cyan, indigo, violet). When these rays hit the screen, they form a dispersion spectrum - a collection of multi-colored stripes. The dispersion spectrum is most clearly revealed when light is refracted in a prism (Figure 4.7).
Figure 4.7
The angle D between the rays corresponding to the extreme colors of the dispersion spectrum is called the dispersion angle. The width of the spectrum depends on it. By the type of spectrum one can judge the chemical composition of the refractive medium. The so-called spectral analysis is based on this.
When light passes through a substance, it is partially absorbed due to the conversion of the electromagnetic energy of the light wave into other types of energy (for example, thermal energy). Substances that weakly absorb light are called transparent. Strongly absorbing light - opaque. This division is relative, since transparency depends not only on the type of substance, but also on the thickness of its layer. In addition, the absorption of light by a substance is selective. Different substances absorb light of different wavelengths differently. This is what determines the color of the body. From a stream of white color, a given body absorbs only rays of a certain wavelength, the rest are transmitted, reflected or scattered and perceived by the human eye. For example, the leaves of living plants have significant absorption in the entire visible spectrum, except for the green and dark red parts.
When light propagates in a homogeneous medium, as shown by the studies of Bouguer and Lambert, the intensity of light changes according to the following law:
(4.1.4)
where I 0 is the intensity of light at the entrance to the layer of matter, I is the intensity of light at the exit from it, x is the thickness of the layer of matter, k is the absorption coefficient, depending on the type of substance and wavelength. Absorption of light ultimately determines all types of effects of light on matter. It is as a result of the action of light that photosynthesis occurs (the transformation of inorganic substances into organic substances accompanied by the release of oxygen).
Passing through a turbid medium (a medium in which many particles of some foreign substance are suspended), light diffracts from its randomly located microhomogeneities and spreads in all directions (scatters). In this case, the environment acquires a blue tint. This phenomenon is explained by Rayleigh's law:
I~1/λ 4 (4.1.5)
those. The intensity of the scattered light is inversely proportional to the fourth power of the wavelength. From formula (4.1.4) it is clear that rays with a shorter wavelength are scattered more strongly (blue light has the shortest wavelength). Light scattering also occurs in media cleared of foreign particles (so-called molecular scattering). In this case, light diffracts from random compactions of the medium caused by the random thermal movement of molecules. In this case, the intensity of the scattered light is low and becomes noticeable when the medium is thick. Molecular scattering explains the blue color of the sky and the yellow color of the solar disk. Because the light passing through the atmosphere consists primarily of long waves.
Near-horizontal arc. Known as the "fire rainbow". Colored bands appear directly in the sky as a result of light passing through ice crystals in cirrus clouds, covering the sky with a “rainbow film”. This natural phenomenon is very difficult to see, as both the ice crystals and sunlight must be at a certain angle to each other to create the "fire rainbow" effect.
“The Ghost of Brocken.” In some areas of the Earth you can observe an amazing phenomenon: a person standing on a hill or mountain, behind whom the sun rises or sets, discovers that his shadow falling on the clouds becomes incredibly huge. This happens because tiny drops of fog refract and reflect sunlight in a special way. The phenomenon got its name from the Brocken peak in Germany, where, due to frequent fogs, this effect can be regularly observed.
Near-zenith arc. A near-zenith arc is an arc centered at the zenith point, located approximately 46° above the Sun. It is rarely visible and only for a few minutes, has bright colors, clear outlines and is always parallel to the horizon. To an outside observer, it will resemble the smile of the Cheshire Cat or an inverted rainbow.
"Foggy" rainbow. The hazy halo looks like a colorless rainbow. Like a regular rainbow, this halo is formed by the refraction of light through water crystals. However, unlike the clouds that form an ordinary rainbow, the fog that creates this halo consists of smaller particles of water, and the light, refracted in tiny droplets, does not color it.
Gloria. When light undergoes backscattering (the diffraction of light previously reflected in the water crystals of a cloud), it returns from the cloud in the same direction in which it fell, creating an effect called "Gloria". This effect can only be observed on clouds that are directly in front of the viewer or below him, at a point that is on the opposite side to the light source. Thus, Gloria can only be seen from a mountain or from an airplane, and the light sources (Sun or Moon) must be directly behind the observer. Gloria's rainbow circles are also called Buddha Light in China. In this photo, a beautiful rainbow halo surrounds the shadow of a hot air balloon as it falls on the cloud below.
Halo at 22?. White circles of light around the Sun or Moon that result from the refraction or reflection of light by ice or snow crystals in the atmosphere are called halos. There are small water crystals in the atmosphere, and when their faces form a right angle with the plane passing through the Sun, the one observing the effect and the crystals will see a characteristic white halo surrounding the Sun in the sky. So the faces reflect light rays with a deviation of 22°, forming a halo. During the cold season, halos formed by ice and snow crystals on the surface of the earth reflect sunlight and scatter it in different directions, creating an effect called “diamond dust”.
Rainbow clouds. When the Sun is positioned at a certain angle to the water droplets that make up the cloud, these droplets refract sunlight and create an unusual “rainbow cloud” effect, coloring it in all the colors of the rainbow. Clouds, like rainbows, owe their colors to different wavelengths of light.
Lunar arc. Dark night skies and the bright light of the Moon often produce a phenomenon called a "lunar rainbow" - a rainbow that appears in the light of the Moon. Such rainbows are located on the opposite side of the sky from the Moon and most often appear completely white. However, sometimes they can be seen in all their glory.
Parhelion. "Parhelium" translated from Greek means "false sun." This is one of the forms of a halo (see point 6): one or more additional images of the Sun are observed in the sky, located at the same height above the horizon as the real Sun. Millions of ice crystals with a vertical surface, reflecting the Sun, form this beautiful phenomenon.
Rainbow. Rainbow is the most beautiful atmospheric phenomenon. Rainbows can take different forms, but the common rule for all of them is the arrangement of colors - in the sequence of the spectrum (red, orange, yellow, green, blue, indigo, violet). Rainbows can be observed when the Sun illuminates part of the sky and the air is saturated with droplets of moisture, for example, during or immediately after rain. In ancient times, the appearance of a rainbow in the sky was given a mystical meaning. Seeing a rainbow was considered a good omen; driving or walking under it promised happiness and success. The double rainbow was said to bring good luck and fulfill wishes. The ancient Greeks believed that the rainbow was a bridge to heaven, and the Irish believed that at the other end of the rainbow was the legendary gold of leprechauns.
Northern Lights. The glow observed in the sky in the polar regions is called the northern, or aurora, as well as the southern - in the Southern Hemisphere). It is assumed that this phenomenon also exists in the atmospheres of other planets, such as Venus. The nature and origin of auroras is the subject of intense research, and numerous theories have been developed in this regard." Auroras, according to scientists, arise from the bombardment of the upper atmosphere by charged particles moving towards the Earth along geomagnetic field lines from the region of near-Earth space, called the plasma layer. The projection of the plasma layer along the geomagnetic field lines onto the earth's atmosphere has the shape of rings surrounding the north and south magnetic poles (auroral ovals).
Condensation trail. Condensation trails are white streaks left in the sky by airplanes. By their nature they are condensed fog, consisting of moisture found in the atmosphere and engine exhaust gases. Most often, these traces are short-lived - under the influence of high temperatures they simply evaporate. However, some of them descend into the lower layers of the atmosphere, forming cirrus clouds. Environmentalists believe that the condensation trails of airplanes transformed in this way have a negative impact on the planet’s climate. Thin high-altitude cirrus clouds, which are obtained from modified aircraft trails, prevent the passage of sunlight and, as a result, lower the temperature of the planet, unlike ordinary cirrus clouds, which are able to retain the heat of the earth.
Rocket exhaust trail. Air currents in high layers of the atmosphere deform the contrails of space rockets, and particles of exhaust gases refract sunlight and paint the contrails in all the colors of the rainbow. Huge multi-colored curls stretch for several kilometers across the sky before evaporating.
Polarization. Polarization is the orientation of electromagnetic oscillations of a light wave in space. Light polarization occurs when light strikes a surface at a certain angle, is reflected, and becomes polarized. Polarized light also travels freely through space, just like regular sunlight, but the human eye is generally unable to detect the change in color shades resulting from the increased polarization effect. This image, taken with a wide-angle lens and a polarizing filter, shows the intense blue color the electromagnetic charge gives to the sky. We can only see such a sky through a camera filter.
Star trail. The “star trail”, invisible to the naked eye, can be captured on a camera. This photo was taken at night, using the camera mounted on a tripod, with the lens aperture wide open and a shutter speed of over an hour. The photograph shows the “movement” of the starry sky - the natural change in the position of the Earth as a result of rotation causes the stars to “move”. The only fixed star is Polaris, which points to the astronomical North Pole.
Zodiacal light. The diffuse glow of the night sky created by sunlight reflected from interplanetary dust particles is also called zodiacal light. The zodiacal light can be observed in the evening in the west or in the morning in the east.
Crown. Coronas are small rings of color around the Sun, Moon or other bright objects that are seen from time to time when the light source is behind translucent clouds. A corona occurs when light is scattered by small water droplets, forming a cloud. Sometimes the corona appears as a luminous spot (or halo) surrounding the Sun (or Moon), which ends in a reddish ring. During eclipses, it is the corona that surrounds the darkened sun.
Twilight rays. Crepuscular rays are diverging beams of sunlight that become visible due to their illumination of dust in the high layers of the atmosphere. The shadows of the clouds form dark stripes, and rays spread between them. This effect occurs when the Sun is low on the horizon before sunset or after dawn.
Mirage. The optical effect caused by the refraction of light when passing through layers of air of different densities is expressed in the appearance of a deceptive image - a mirage. Mirages can be observed in hot climates, especially in deserts. The smooth surface of the sand in the distance looks like an open source of water, especially when viewed in the distance from a dune or hill. A similar illusion occurs in the city on a hot day, on the asphalt heated by the rays of the sun. In fact, the “water surface” is nothing more than a reflection of the sky. Sometimes mirages show entire objects located at a great distance from the observer.
Columns of light. Flat ice crystals reflect light in the upper atmosphere and form vertical columns of light, as if emerging from the earth's surface. Light sources can be the Moon, the Sun or artificial lights.
And this phenomenon, which the inhabitants of the island of Madeira, in the Atlantic Ocean, once observed, defies any classification.
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Abstract on physics
on the topic: “Light phenomena in nature”
students of 8th grade "L 1st"
Introduction
Why is the sky blue and the sunset red?
Tyndall's experience
Light Scattering
Air fluctuation
Green beam
"Blind" strip
Refraction
Ice crystals in the clouds
Halo in Antarctica
Upper mirages
"Ghost" lands
"Flying Dutchman"
Inferior Mirages
Side mirages
Fata Morgana
Misty Rainbow
Moon Rainbow
Auroras
Types of auroras
The influence of the aurora
Conclusion
Bibliography
Introduction
There are so many amazing things in nature! Light phenomena look especially unusual and fascinating. Since ancient times, people have perceived this as a miracle, associating the inexplicable with mystical forces or with the gods.
I became interested: there is an explanation for all these unusual phenomena. And I decided to take a new look, from a physical point of view, at some light phenomena and find answers to many questions of interest.
The sun is the source of energy for the life of plants and animals. It creates winds, heating vast land masses and the air masses above them, and serves as the driving force for the water cycle in nature, lifting water vapor into the atmosphere. The sun is a vital component of the environment, without which life on Earth would be impossible.
The sun's rays illuminate the entire globe. The world of sunlight is beautiful. He brings joy to everyone living on Earth. The world of sunlight is huge, diverse, inexhaustible.
The firmament is infinitely beautiful, and light phenomena also look beautiful and amazing: sunset, “blind streak”, green beam, rainbow, northern lights, halo, mirages. In this essay, phenomena that are inextricably linked with Sunlight will be considered, many wonders of nature will be explained.
Whythe sky is blue and the sunset is red
The sun... Already in ancient times, people understood that without the sun's rays life on Earth would be impossible. They called the sun “the beginning of life,” deified it, and worshiped it. At all times, sunset has evoked sadness, fear, and anxiety in people, but more often a sunset evokes a slight sadness bordering on peace. The observed picture of a sunset depends each time on the state of the atmosphere and is largely determined by the type and shape of the clouds illuminated by the rays of the setting sun. That's why one sunset is so different from another. And sunsets are always extraordinarily beautiful.
First of all, what catches your eye is the reddish color of the setting Sun and the same color of the sky near it. Near the horizon line it is redder, and in the upper part of the disk it turns into a lighter color.
Tyndall's experience
The sky is blue and the color of the setting sun turns red. In both cases, the reason is the same - the scattering of sunlight in the earth's atmosphere. This can be explained by assuming that blue light is scattered more than red light. This was proven in 1869 when J. Tyndall performed his famous experiment. This experience is not at all difficult to reproduce. Let's take a rectangular aquarium, fill it with water and direct a weakly diverging narrow beam of light from an overhead projector onto the wall of the aquarium. The experiment should be carried out in a darkened room. To enhance the scattering of the light beam as it passes through the aquarium, add a little milk to the water. The fat particles contained in milk do not dissolve in water; they are in suspension and contribute to the scattering of light. You can observe a bluish tint in diffused light. The light passing through the aquarium acquires a reddish tint. So, if you look at the light beam in the aquarium from the side, it appears bluish, and from the exit end it appears reddish. This can be explained by the fact that when a white light beam passes through a scattering medium, mainly the “blue component” is scattered from it, so the “red component” begins to predominate in the beam emerging from the medium.
Light Scattering
In 1871, J. Strett explained the results of Tyndall’s experiments in exactly this way. He developed a theory of scattering of light waves by particles whose dimensions are much smaller than the wavelength of light. The law established by Rayleigh states: The intensity of scattered light is proportional to the fourth power frequency of light, or, in other words, is inversely proportional to the fourth power of the light wavelength.
If we apply Rayleigh's law to the scattering of sunlight in the Earth's atmosphere, then it is not difficult to explain the blue color of the daytime sky and the red color of the sun at sunrise and sunset. Since light waves with higher frequencies are scattered more intensely, then, consequently, the spectrum of the scattered light will be shifted towards higher frequencies, and the spectrum of the light remaining in the beam after the light that has experienced scattering has left the beam will be shifted in the opposite direction - to higher frequencies. low frequencies. In the first case, the white color becomes blue, and in the second, reddish. Looking at the daytime sky, the observer perceives light scattered in the atmosphere; According to Rayleigh's law, the spectrum of this light is shifted towards higher frequencies, hence the blue color of the sky. Looking at the sun, the observer perceives light that has passed through the atmosphere without scattering; the spectrum of this color will be shifted to lower frequencies. The closer the sun is to the horizon, the longer the path in the atmosphere light rays travel before reaching the observer, the more their spectrum shifts. As a result, we see the setting and rising sun in red tones. It is also understandable why the lower part of the setting solar disk appears redder than its upper part.
The main role is played by the dependence of the intensity of light scattering on its frequency. But what is the nature of those centers on which light waves are scattered? Initially, it was thought that the role of such centers was played by tiny specks of dust and droplets of water, but this does not explain the wonderful blue color of the sky in high mountain areas, where the air is very clean and dry.
Air fluctuation
In 1899, Rayleigh put forward a hypothesis according to which the centers that scatter light are the air molecules themselves. In the first half of the twentieth century, thanks to the work of M. Smoluchowski, A. Einstein and L. I. Mandelstam, it was established that in fact light scattering occurs not on the air molecules themselves, but on somewhat unusual objects that arise as a result of the chaotic movement of the thermal movement of molecules , - on fluctuations in air density, i.e., randomly occurring microscopic condensations and rarefactions of air. We see that some cells turn out to be almost empty, and some are relatively densely populated with molecules. This is a consequence of the chaotic thermal movement of air molecules. As a result, the density of atmospheric air will randomly change (fluctuate) from one cell to another. It is clear that at a different moment in time other cells will be more or less populated, but the air density will still change randomly. The concept of air density fluctuations can be explained in another way. Let us focus our attention not on any specific moment in time, but on some arbitrarily chosen cell of space. Over time, the number of molecules in a cell will fluctuate, where several different times are considered. Simply put, the density of the air at a given point will vary randomly over time. These local inhomogeneities in air density are the scattering centers that determine the blue color of the daytime sky and the red color of the setting sun. The presence of fine dust and water droplets in the air leads to additional scattering and to some extent affects the color of the sky and sunset. However, the root cause is the scattering of light by air density fluctuations. The nature of these fluctuations largely depends on the state of the atmosphere: the temperature of various layers of air, the nature and strength of the wind. That is why in calm, clear weather the sunset is golden, and in windy weather it is purple.
Green beam
An amazing sight - a green ray. A bright green light flashes for a few seconds when almost the entire solar disk has disappeared beyond the horizon. This can be seen on such evenings when the Sun shines brightly until sunset and almost does not change its color. It is important that the horizon has a distinct line without any irregularities: forests, buildings, etc. These conditions are easiest to achieve at sea.
The appearance of the green ray can be explained by taking into account the change in refractive index with the frequency of light. Typically, the refractive index increases with increasing frequency. Higher frequency rays are refracted more strongly. This means that blue-green rays undergo stronger refraction compared to red rays
Let us assume that there is refraction of light in the atmosphere, but there is no scattering of light. In this case, the upper and lower edges of the solar disk near the horizon line would have to be colored in the colors of the rainbow. For simplicity, let there be only two colors in the spectrum of sunlight - green and red; The “white” solar disk can be considered in this case in the form of green and red disks superimposed on each other. The refraction of light in the atmosphere raises the green disk above the horizon to a greater extent than the red one. The upper edge of the solar disk would be green and the lower edge red; in the central part of the disk a mixture of colors would be observed, i.e., a white color would be observed.
In reality, one cannot ignore the scattering of light in the atmosphere. As we already know, it leads to the fact that rays with a higher frequency are eliminated more efficiently from the light beam coming from the sun. So we won’t see the green border on top of the disk, and the entire disk will look reddish rather than white. If, however, almost the entire solar disk has gone beyond the horizon, only its very upper edge remains, and the weather is clear and calm, the air is clean (so light scattering is minimal), then in this case we can see the bright green edge of the sun along with a scattering of bright, green rays. And yet we will see green, because blue has scattered in the atmosphere.
"Blind» band
Another amazing phenomenon: sometimes the Sun seems to set not behind a clearly visible horizon line, but behind some invisible line located above the horizon. Interestingly, this phenomenon is observed in the absence of any cloudiness. If you quickly climb to the top of the hill, you can observe an even stranger picture: now the sun sets behind the horizon, but at the same time the solar disk appears to be cut off by a horizontal blind stripe. The sun gradually sinks lower and lower, and the position of the blind strip in relation to the horizon remains unchanged.
The sunset pattern is observed if the air near the earth's surface is quite cold, and above there is a layer of relatively warm air. In this case, the refractive index of air changes with altitude a) The transition from the lower cold layer of air to the warm layer above it can lead to a rather sharp decrease in the refractive index. For simplicity, we assume that this decline occurs abruptly, therefore, between the cold and warm layers there is a clearly defined interface located at a certain height h0 above the earth's surface. The mentioned jump b) where nx denotes the refractive index of air in the cold layer, and nt - in the warm layer near the border with the cold one.
Refraction
The time of sunrise and sunset anywhere on the globe on any day of the year is calculated quite accurately using astronomical formulas. But in fact, the calculated time of sunrise and sunset and the actual time do not always coincide. The fact is that the atmosphere surrounding the Earth makes its “adjustments”.
Air density decreases rapidly with altitude. Along with density, the refractive index and the speed of propagation of electromagnetic waves in the atmosphere change.
Refraction is called the refraction of electromagnetic waves in the atmosphere due to the inhomogeneity of air density, both in the horizontal and, especially strongly, in the vertical directions. The trajectories of electromagnetic waves in the atmosphere are complex curves.
A direct consequence of the refraction of sunlight is an increase in the length of the day. When the Sun sets, when its disk has already sunk below the horizon, refraction lifts it, and the day still continues. Similarly at sunrise: the Sun is still below the horizon, but due to refraction we already see it, that is, the day begins before the actual sunrise.
The increase in day length depends on the latitude of the place and the declination of the Sun on a given day. In middle latitudes, due to refraction, the day usually increases by no more than 8 - 12 minutes. If we move along the earth's surface towards the poles, the lengthening of the day becomes more and more significant. At the poles of the globe, where the polar day and polar night should last exactly six months, it turns out that the polar day is 14 days longer than the polar night.
Halo
When the Sun or Moon shines through thin cirrostratus clouds made of ice crystals, light phenomena called halos often appear in the sky. Halo phenomena are very diverse.
At moments close to sunset or sunrise, pillars of light appear above the Sun, and sometimes below it.
The frequency of the halo is determined by the frequency of occurrence of cirrostratus clouds. Often several halo forms are observed in the sky at the same time. A complex complex of various halos was observed in St. Petersburg on July 18, 1794. 12 different circles and arcs were simultaneously observed in the sky, 9 of them were colored. Other complex halos have been described that have been observed in different places around the globe.
The appearance in the sky at the same time of several suns, light crosses, oblique arcs, which, especially during dawn, seemed like “bloody swords”, in former times caused fear in people, gave rise to superstition, and was perceived as a harbinger of great trouble - war, famine.
Ice crystals in the clouds
How do halos arise? All halo shapes are the result of the refraction of solar or lunar rays in the ice crystals of the cloud or their reflection from the side faces or bases of crystals shaped like hexagonal columns or plates. Strictly speaking, diffraction of solar or lunar rays occurs on crystals.
Halo in Antarctica
Most often, various halos appear at inland stations located on the ice dome of Antarctica and on its slope at altitudes of 2700 - 3500 m above sea level.
In the absence of dense snow clouds, when the Sun shines, unusually bright colored and white halos appear. Often only the lower halves of the halo circles are visible.
Halos in Antarctica are often observed throughout the whole day; only their shape and brightness of colors change.
Another interesting light phenomenon that has only been seen in the depths of the Antarctic continent is rainbow, or colored, drifting snow. It is observed only when the Sun is low, and in order to see it better, you need to lie down on the snow and look towards the Sun. The drifts of drifting snow quickly moved by the wind, encountering sastrugi of snow on their way, fly up, forming small and large multi-colored fountains, flashing with all the colors of the rainbow.
Colored drifting snow occurs as a result of the refraction of sunlight in the hollow ice crystals that make up the drifting snow and in the crystals that settle from clouds. The origin of colored drifting snow is similar to the “play” of light in crystal chandeliers, pendants, and diamond jewelry.
Mirages
The word mirage is of French origin and has two meanings: “reflection” and “deceptive vision.” Both meanings of this word well reflect the essence of the phenomenon. A mirage is an image of an object that actually exists on Earth, often enlarged and greatly distorted. A mirage can be sketched, photographed, filmed, which has been done many times. There are several types of mirages depending on where the image is located in relation to the object. Mirages are: upper, lower, lateral and complex. refraction solar fluctuation drifting snow
The most frequently observed upper and lower mirages occur with an unusual distribution of density over height, when at a certain height or near the very surface of the Earth there is a relatively thin layer of very warm air in which rays coming from ground objects experience complete internal reflection.
Upper mirages
In superior mirages, the image is located above the object. Such mirages occur when air density and refractive index rapidly decrease with altitude.
Over cold seas or over cooled land surfaces, an expansion of the horizon is often observed. The earth seems to straighten out a little, and very distant objects rise from the horizon and become visible.
"Ghostly"heat
Apparently, the number of upper mirages should include at least part of the so-called ghostly lands, which were searched for decades in the Arctic and were never found. These are the Lands of Andreev, Gilles, Oscar, Sannikov and others. They searched for Sannikov Land for a particularly long time.
In 1811, Sannikov set off on dogs across the ice to the group of New Siberian Islands and from the northern tip of Kotelny Island saw an unknown island in the ocean. He was unable to reach it - huge ice holes were in the way. Sannikov reported the discovery of a new island to the tsarist government. In August 1886 E.V. Tol, during his expedition to the New Siberian Islands, also saw Sannikov Island.
Tol gave 16 years of his life to the search for Sannikov Land. He organized and conducted three expeditions to the New Siberian Islands area. During the last expedition on the schooner "Zarya", Tolya's expedition died without finding Sannikov Land. No one saw Sannikov Land again. Perhaps it was a mirage that appears in the same place at certain times of the year. Both Sannikov and Tol saw a mirage of the same island located in this direction, only much further in the ocean.
English polar explorer Robert Scott suggested in 1902 that there was a mountain range further beyond the horizon. Indeed, the mountain range was later discovered by the Norwegian polar explorer Roald Amundsen and exactly where Scott expected it to be.
"Flying Dutchman"
The Flying Dutchman is a ghostly sailing ship of unusually large size with no visible crew on board. It suddenly appeared, walked silently, not responding to signals, and just as suddenly disappeared. A meeting with the Flying Dutchman was considered fatal; one had to wait for a storm or other disaster.
It was, without a doubt, a superior mirage, that is, an image of some ordinary sailing ship that was calmly sailing somewhere far beyond the horizon, and its enlarged and distorted image, in the form of a superior mirage, rose into the air, and was mistaken for “ The Flying Dutchman." Mirage, naturally, did not respond to any signals from other ships. Now the “Flying Dutchman” in the form of a sailing ship has disappeared from the seas and oceans, since sailing ships have become rare. You can see mirages of ships sailing beyond the visible horizon quite often.
Inferior Mirages
Inferior mirages occur when temperature decreases very quickly with height. A mirage is called an inferior mirage because the image of an object is placed under the object. In lower mirages, it seems as if there is a water surface under the object, and all objects are reflected in it.
Reflection in a thin layer of air heated from the earth's surface is completely similar to reflection in water. Only the air itself plays the role of a mirror. The air condition in which inferior mirages occur is extremely unstable. After all, below, near the ground, lies highly heated, and therefore lighter, air, and above it lies colder and heavier air. Jets of hot air rising from the ground penetrate layers of cold air. Due to this, the mirage changes before our eyes, the surface of the “water” seems to be agitated. A small gust of wind or a push is enough and collapse will occur, that is, the air layers will turn over. Heavy air will rush down, destroying the air mirror, and the mirage will disappear.
Favorable conditions for the occurrence of inferior mirages are a homogeneous, flat underlying surface of the Earth, which occurs in steppes and deserts, and sunny, windless weather.
The apparent surface of water or lake seen in a mirage is actually a reflection of the sky. Parts of the sky are reflected in the air mirror and create the complete illusion of a shiny water surface. Such mirages are visible in the summer, on sunny days over asphalt roads or a flat sandy beach.
Side mirages
Lateral mirages can occur when layers of air of the same density are located obliquely or even vertically in the atmosphere. Such conditions are created in the summer, in the morning shortly after sunrise, on the rocky shores of the sea or lake, when the shore is already illuminated by the Sun, and the surface of the water and the air above it are still cold. A side mirage can appear near a stone wall of a house heated by the Sun, and even on the side of a heated stove.
Fata Morgana
Complex types of mirages, or Fata Morgana, occur when there are simultaneously conditions for the appearance of both an upper and lower mirage. The air density first increases with height and then also quickly decreases. With such a distribution of air density, the state of the atmosphere is very unstable and subject to sudden changes. Therefore, the appearance of the mirage changes before our eyes. The most ordinary rocks and houses, due to repeated distortions and magnification, turn into the wonderful castles of the fairy Morgana before our eyes.
Rainbow
A commonly observed rainbow is an arc of color visible against a curtain of rain showers or streaks of falling rain, often not reaching the surface of the earth. A rainbow is visible in the direction of the sky opposite the Sun, and always when the Sun is not covered by clouds. Such conditions are most often created during summer rainfall.
Most people who have observed a rainbow many times do not see, or rather do not notice, additional arcs in the form of the most delicate colored arches inside the first and outside the second rainbow. These color arcs are incorrectly called supplementary - in reality they are as basic as the first and second rainbows. These arcs do not form a whole semicircle or large arc and are only visible in the very top parts of the rainbow. It is in these arcs, and not in the main ones, that the greatest wealth of pure color tones is concentrated.
All rainbows are sunlight broken down into its components and moved across the sky in such a way that it appears to come from the part of the sky opposite to where the Sun is located.
The entire appearance of the rainbow - the width of the arcs, the presence, location and brightness of individual color tones, the position of additional arcs very much depend on the size of the raindrops.
By the appearance of the rainbow, you can approximately estimate the size of the raindrops that formed this rainbow. In general, the larger the raindrops, the narrower and brighter the rainbow is; large drops are especially characterized by the presence of a rich red color in the main rainbow. Numerous additional arcs also have bright colors and are directly adjacent to the main rainbows, without gaps. The smaller the droplets, the wider and fainter the rainbow becomes, with an orange or yellow edge. From the surface of the Earth, we can observe a rainbow in the best case in the form of a half circle when the Sun is on the horizon. From an airplane you can see a rainbow in the form of a whole circle.
Misty Rainbow
White rainbows occur in nature. They appear when the sun illuminates a weak fog consisting of droplets with a radius of 0.025 mm or less. They are called misty rainbows. In addition to the main rainbow in the form of a brilliant white arc with a barely noticeable yellowish edge, sometimes colored additional arcs are observed: a very weak blue or green arc, and then a whitish-red one. A similar type of white rainbow can be seen when a spotlight behind you illuminates intense haze or light fog in front of you. Even a street lamp can create, albeit a very faint, white rainbow, visible against the dark background of the night sky.
Moon Rainbow
Similar to solar ones, lunar rainbows can also appear. They are weaker and appear during the full moon. Lunar rainbows are a rarer phenomenon than solar rainbows. For their occurrence, a combination of two conditions is necessary: a full Moon, not covered by clouds, and heavy rain. Moonbows can be observed anywhere on the globe where the above two conditions are met.
Daytime, solar rainbows, even those formed by the smallest drops of rain or fog, are quite whitish and light, and yet their outer edge is at least faintly colored orange or yellow. Rainbows formed by moon rays do not live up to their name at all, since they are not iridescent and look like light, completely white arcs.
The absence of red color in the lunar arcs, even with large drops of heavy rain, is explained by the low level of illumination at night, at which the sensitivity of the eye to red rays is completely lost. The remaining colored rays of the rainbow also lose much of their color tone due to the lack of color in human night vision.
Auroras
Aurora borealis are flashes of light in the form of bright colored stripes. Auroras occur when electrons and protons flying from space collide with atoms and molecules in the upper atmosphere. The collision results in the emission of light - sometimes white, but more often green and red. After a solar flare, auroras are always brighter and can be observed at latitudes closer to the equator.
The ancient Romans called the goddess of the dawn Aurora. They also associated auroras, occasionally observed at mid-latitudes, with her name. After all, like the morning dawn, these lights were colored pink and red. With the light hand of the Romans, the term “aurora” subsequently began to be applied to the auroras. Currently, this term has become established in the scientific literature; all phenomena associated with auroras are now commonly called auroral phenomena.
Types of auroras
The polar lights are always an unusually majestic spectacle. Polar lights are very diverse. But despite all the diversity, several specific forms can be distinguished. There are usually four main forms.
The simplest form is homogeneous arc (uniform stripe). It has a fairly even glow, brighter at the bottom of the arc and gradually disappearing at the top. The arc usually extends across the entire sky in the east-west direction; its length reaches thousands of kilometers, while its thickness is only a few kilometers. The length of the luminous stripe in the vertical direction is measured in hundreds of kilometers; the lower edge of the strip is, as a rule, at altitudes of 100-150 km. Uniform arcs (stripes) are whitish-green, as well as reddish or purple.
The next form of aurora -- rays . In the sky, narrow vertical luminous lines closely lined up one after another are visible, as if many powerful searchlights placed in a row are shining upward. For an observer who looks at the aurora not from the side, but directly from below, the rays appear to be converging in the heights (perspective effect). Starting from an altitude of approximately 100 km, the rays extend upward for hundreds and even thousands of kilometers. Together they form a radiant stripe. It is usually greenish in color; below the stripe often has a pinkish-orange border.
Particularly impressive are the glows that have the shape tapes , which can form folds or twist into peculiar spirals. Giant curtains hang high in the sky, they sway, wave, change shape and brightness. The thickness of these curtains is about a kilometer; in height they range from approximately 100 to 400 km. The color of the ribbons is mainly greenish-blue, with a transition to pinkish and red tones in the lower part.
Finally, we should note the auroras that have the shape of blurry spots , similar to giant glowing clouds; they are called diffuse spots. An individual spot of this type has an area of about 100 km². As a rule, the spots are whitish or reddish in color. They are formed at altitudes of about 100 km, as well as at altitudes of 400...500 km. Different forms of auroras can occur simultaneously, overlapping one another.
Rays, ribbons, spots are not stationary at all: they move and at the same time the intensity of their glow changes over time. The speed of movement of rays and ribbons can reach tens of kilometers per second. During the night, one can observe the gradual transformation of some forms of auroras into others. For example, a uniform arc can suddenly break into rays or turn into folds of a ribbon, and the latter can then disintegrate into cloud-like spots.
Influencepolarradiance
At one time, the appearance of auroras was associated with tragic phenomena in nature and society. Is it only fear of incomprehensible, impressive natural phenomena that underlies these superstitions? It is now well known that solar rhythms with different periods (27 days, 11 years, etc.) affect various aspects of life on Earth. Solar and magnetic storms (and associated auroras) can cause an increase in various diseases, including diseases of the human cardiovascular system. Solar cycles are associated with climate changes on Earth, the occurrence of droughts and floods, earthquakes, etc. All this makes us once again seriously think about the connection between the auroras and earthly cataclysms and misfortunes. Maybe the old ideas about such a connection are not so stupid?
Auroras signal the place and time of the influence of the Cosmos on earthly processes. The incursion of charged particles that causes them affects many aspects of our lives. The ozone content and the electrical potential of the ionosphere change, and the heating of the ionospheric plasma excites waves in the atmosphere. All this affects the weather. Due to additional ionization, significant electric currents begin to flow in the ionosphere, the magnetic fields of which distort the Earth's magnetic field, which directly affects the health of many people. Thus, through auroras and related processes, the Cosmos influences the nature around us and its inhabitants.
Conclusion
Writing the essay was entertaining and interesting: I not only presented information, but also learned interesting things with interest.
After writing my essay, I learned about some phenomena that I had never seen. Now I will watch the sky more often: I really want to see some phenomena for which I already know the explanation. I was especially interested in such things as the green beam, the “blind” stripe and mirages. And some phenomena are no longer incomprehensible to me: after all, everything has an explanation from a physical point of view, it’s just that not everything has been studied yet.
I learned why the sky is blue, how and where light is scattered in the atmosphere, what fluctuation is, how a rainbow is formed and much more. But there are still many mysteries in nature, no less interesting.
Bibliography
1. Tarasov "Physics in Nature"
2. Ian Nicholson translated by V. N. Mikhailov Encyclopedia "Universe"
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