1. Optical phenomena in the atmosphere were the first optical effects that were observed by man. With the understanding of the nature of these phenomena and the nature of human vision, the formation of the problem of light began.

The total number of optical phenomena in the atmosphere is very large. Only the most famous phenomena will be considered here - mirages, rainbows, halos, crowns, twinkling stars, blue sky and scarlet dawn. The formation of these effects is associated with such properties of light as refraction at the interfaces between media, interference and diffraction.

2. atmospheric refraction – is the curvature of light rays as they pass through the planet's atmosphere. Depending on the sources of rays, there are astronomical and terrestrial refraction. In the first case, the rays come from celestial bodies (stars, planets), in the second case, from terrestrial objects. As a result of atmospheric refraction, the observer sees an object not where it is, or not in the shape that it has.

3. Astronomical refraction was already known in the time of Ptolemy (2nd century AD). In 1604, I. Kepler suggested that the earth's atmosphere has a height-independent density and a certain thickness h(Fig. 199). Ray 1 coming from the star S straight to the observer A in a straight line, will not fall into his eye. Refracted at the boundary of vacuum and atmosphere, it will hit the point AT.

Ray 2 will hit the observer's eye, which, in the absence of refraction in the atmosphere, would have to pass by. As a result of refraction (refraction), the observer will see the star not in the direction S, but on the continuation of the beam refracted in the atmosphere, that is, in the direction S 1 .

Injection γ , which deviates to the zenith Z apparent position of the star S 1 compared to true position S, called refractive angle. At the time of Kepler, the angles of refraction were already known from the results of astronomical observations of some stars. Therefore, Kepler used this scheme to estimate the thickness of the atmosphere h. According to his calculations, h» 4 km. If we count by the mass of the atmosphere, then this is about half the true value.

In fact, the density of the Earth's atmosphere decreases with altitude. Therefore, the lower layers of air are optically denser than the upper ones. Rays of light traveling obliquely to the Earth are not refracted at one point of the boundary between vacuum and atmosphere, as in Kepler's diagram, but are bent gradually along the entire path. This is similar to how a beam of light passes through a stack of transparent plates, the refractive index of which is the greater, the lower the plate is located. However, the total effect of refraction manifests itself in the same way as in the Kepler scheme. We note two phenomena due to astronomical refraction.

a. The apparent positions of celestial objects are shifting towards the zenith to the angle of refraction γ . The lower the star is to the horizon, the more noticeably its apparent position in the sky rises compared to the true one (Fig. 200). Therefore, the picture of the starry sky, observed from the Earth, is somewhat deformed towards the center. Only the dot does not move S located at the zenith. Due to atmospheric refraction, stars that are slightly below the geometric horizon line can be observed.

Refraction angle values γ decrease rapidly as the angle increases. β the height of the luminary above the horizon. At β = 0 γ = 35" . This is the maximum angle of refraction. At β = 5º γ = 10" , at β = 15º γ = 3" , at β = 30º γ = 1" . For luminaries whose height β > 30º, refractive shift γ < 1" .

b. The sun illuminates more than half of the earth's surface.. Rays 1 - 1, which in the absence of an atmosphere should touch the Earth at the points of the diametrical section DD, thanks to the atmosphere, they touch it a little earlier (Fig. 201).

The surface of the Earth is touched by rays 2 - 2, which would pass by without the atmosphere. As a result, the terminator line BB, separating light from shadow, shifts to the region of the night hemisphere. Therefore, the area of ​​the day surface on Earth is greater than the area of ​​the night.

4. Earth refraction. If the phenomena of astronomical refraction are due global refractive effect of the atmosphere, then the phenomena of terrestrial refraction are due local atmospheric changes usually associated with temperature anomalies. The most remarkable manifestations of terrestrial refraction are mirages.

a. superior mirage(from fr. mirage). It is usually observed in arctic regions with clear air and low surface temperatures. The strong cooling of the surface here is due not only to the low position of the sun above the horizon, but also to the fact that the surface covered with snow or ice reflects most of the radiation into space. As a result, in the surface layer, as it approaches the Earth's surface, the temperature decreases very quickly and the optical density of air increases.

The curvature of the rays towards the Earth is sometimes so significant that objects are observed that are far beyond the line of the geometric horizon. Beam 2 in Fig. 202, which in an ordinary atmosphere would have gone into its upper layers, in this case is bent towards the Earth and enters the observer's eye.

Apparently, just such a mirage is the legendary "Flying Dutchmen" - the ghosts of ships that are actually hundreds or even thousands of kilometers away. What is surprising in superior mirages is that there is no noticeable decrease in the apparent size of the bodies.

For example, in 1898 the crew of the Bremen ship "Matador" observed a ghost ship, the apparent dimensions of which corresponded to a distance of 3-5 miles. In fact, as it turned out later, this ship was at that time at a distance of about a thousand miles. (1 nautical mile equals 1852 m). Surface air not only bends light rays, but also focuses them as a complex optical system.

Under normal conditions, the air temperature decreases with increasing altitude. The reverse course of temperature, when the temperature rises with increasing altitude, is called temperature inversion. Temperature inversions can occur not only in the Arctic zones, but also in other, lower latitude places. Therefore, superior mirages can occur wherever the air is sufficiently clean and where temperature inversions occur. For example, distant vision mirages are sometimes observed on the Mediterranean coast. Temperature inversion is created here by hot air from the Sahara.

b. inferior mirage occurs during the reverse course of temperature and is usually observed in deserts during hot weather. By noon, when the sun is high, the sandy soil of the desert, consisting of particles of solid minerals, warms up to 50 degrees or more. At the same time, at a height of several tens of meters, the air remains relatively cold. Therefore, the refractive index of the above air layers is noticeably greater compared to the air near the ground. This also leads to the curvature of the rays, but in the opposite direction (Fig. 203).

Rays of light coming from the parts of the sky located low above the horizon, which are opposite the observer, are constantly bent upward and enter the eye of the observer in the direction from the bottom up. As a result, on their continuation on the surface of the earth, the observer sees a reflection of the sky, resembling a water surface. This is the so-called "lake" mirage.

The effect is even more enhanced when there are rocks, hills, trees, buildings in the direction of observation. In this case, they are visible as islands in the middle of a vast lake. Moreover, not only the object is visible, but also its reflection. By the nature of the curvature of the rays, the ground layer of air acts as a mirror of the water surface.

5. Rainbow. It's colorful an optical phenomenon observed during rain, illuminated by the sun and representing a system of concentric colored arcs.

The first theory of the rainbow was developed by Descartes in 1637. By this time, the following experimental facts related to the rainbow were known:

a. The center of the rainbow O is on the straight line connecting the Sun with the observer's eye.(fig.204).

b. Around the line of symmetry Eye - the Sun is a colored arc with an angular radius of about 42° . The colors are arranged, counting from the center, in the order: blue (d), green (h), red (k)(line group 1). This is main rainbow. Inside the main rainbow there are faint multi-colored arcs of reddish and greenish hues.

in. The second system of arcs with an angular radius of about 51° called the secondary rainbow. Its colors are much paler and go in reverse order, counting from the center, red, green, blue (a group of lines 2) .

G. The main rainbow appears only when the sun is above the horizon at an angle of no more than 42 °.

As Descartes established, the main reason for the formation of the primary and secondary rainbows is the refraction and reflection of light rays in raindrops. Consider the main provisions of his theory.

6. Refraction and reflection of a monochromatic beam in a drop. Let a monochromatic beam with intensity I 0 falls on a spherical drop of radius R on distance y from the axis in the plane of the diametrical section (Fig. 205). At the point of fall A part of the beam is reflected, and the main part of the intensity I 1 passes inside the drop. At the point B most of the beam passes into the air (in Fig. 205 AT beam not shown), and a smaller part is reflected and falls to a point With. Stepped out at the point With beam intensity I 3 is involved in the formation of the main bow and weak secondary bands within the main bow.

Let's find the corner θ , under which the beam comes out I 3 with respect to the incident beam I 0 . Note that all the angles between the ray and the normal inside the drop are the same and equal to the angle of refraction β . (Triangles OAB and OVS isosceles). No matter how much the beam “circles” inside the drop, all angles of incidence and reflection are the same and equal to the angle of refraction β . For this reason, any ray emerging from the drop at the points AT, With etc., exits at the same angle equal to the angle of incidence α .

To find an angle θ beam deflection I 3 from the original, it is necessary to sum the deviation angles at points BUT, AT and With: q = (α – β) + (π – 2β) + (α - β) = π + 2α – 4β . (25.1)

It is more convenient to measure an acute angle φ \u003d π - q \u003d 4β – 2α . (25.2)

Having performed the calculation for several hundred rays, Descartes found that the angle φ with growth y, that is, as the beam moves away I 0 from the drop axis, first grows in absolute value, at y/R≈ 0.85 takes on a maximum value and then begins to decrease.

Now this is the limit value of the angle φ can be found by examining the function φ to the extreme at. Since sin α = yçR, and sin β = yçR· n, then α = arcsin( yçR), β = arcsin( yçRn). Then

, . (25.3)

Expanding the terms into different parts of the equation and squaring, we get:

, Þ (25.4)

For yellow D-sodium lines λ = 589.3 nm refractive index of water n= 1.333. Point distance BUT occurrences of this ray from the axis y= 0,861R. The limiting angle for this ray is

Interesting that the point AT the first reflection of the beam in the drop is also the maximum distance from the drop axis. Exploring at an extreme angle d= p– α – ε = p– α – (p– 2β ) = 2β – α in size at, we get the same condition at= 0,861R and d= 42.08°/2 = 21.04°.

Figure 206 shows the dependence of the angle φ , under which the beam leaves the drop after the first reflection (formula 25.2), on the position of the point BUT beam entry into the drop. All rays are reflected inside a cone with an apex angle of ≈ 42º.

It is very important for the formation of a rainbow that the rays entering the drop in a cylindrical layer of thickness uçR from 0.81 to 0.90, come out after reflection in the thin wall of the cone in the angular range from 41.48º to 42.08º. Outside, the wall of the cone is smooth (there is an extremum of the angle φ ), from the inside - loose. The angular thickness of the wall is ≈ 20 arc minutes. For transmitted rays, the drop behaves like a lens with a focal length f= 1,5R. Rays enter the drop over the entire surface of the first hemisphere, are reflected back by a diverging beam in the space of a cone with an axial angle of ≈ 42º, and pass through a window with an angular radius of ≈ 21º (Fig. 207).

7. The intensity of the rays emerging from the drop. Here we will only talk about the rays that emerged from the drop after the first reflection (Fig. 205). If a beam incident on a drop at an angle α , has intensity I 0 , then the beam that has passed into the droplet has an intensity I 1 = I 0 (1 – ρ ), where ρ is the intensity reflection coefficient.

For unpolarized light, the reflection coefficient ρ can be calculated using the Fresnel formula (17.20). Since the formula includes the squares of the functions of the difference and the sum of the angles α and β , then the reflection coefficient does not depend on whether the beam enters the droplet or from the droplet. Because the corners α and β at points BUT, AT, With are the same, then the coefficient ρ at all points BUT, AT, With the same. Hence, the intensity of the rays I 1 = I 0 (1 – ρ ), I 2 = I 1 ρ = I 0 ρ (1 – ρ ), I 3 = I 2 (1 – ρ ) = I 0 ρ (1 – ρ ) 2 .

Table 25.1 shows the values ​​of the angles φ , coefficient ρ and intensity ratios I 3 cI 0 calculated at different distances uçR beam entry for yellow sodium line λ = 589.3 nm. As can be seen from the table, when at≤ 0,8R into the beam I 3, less than 4% of the energy from the beam incident on the drop falls. And only starting from at= 0,8R and more up to at= R output beam intensity I 3 is multiplied.

Table 25.1
y/R	α ,º	β ,º	φ ,º	ρ	I 3 /I 0
0	0	0	0	0,020	0,019
0,30	17,38	12,94	16,99	0,020	0,019
0,50	29,87	21,89	27,82	0,021	0,020
0,60	36,65	26,62	33,17	0,023	0,022
0,65	40,36	29,01	35,34	0,025	0,024
0,70	44,17	31,52	37,73	0,027	0,025
0,75	48,34	34,09	39,67	0,031	0,029
0,80	52,84	36,71	41,15	0,039	0,036
0,85	57,91	39,39	42,08	0,052	0,046
0,90	63,84	42,24	41,27	0,074	0,063
0,95	71,42	45,20	37,96	0,125	0,095
1,00	89,49	48,34	18,00	0,50	0,125

So, the rays emerging from the drop at the limiting angle φ , have a much greater intensity compared to other beams for two reasons. Firstly, due to the strong angular compression of the beam of rays in the thin wall of the cone, and secondly, due to lower losses in the droplet. Only the intensity of these rays is sufficient to evoke in the eye a sensation of the brilliance of a drop.

8. Formation of the main rainbow. When light falls on a drop, the beam splits due to dispersion. As a result, the wall of the cone of bright reflection is stratified by colors (Fig. 208). purple rays ( l= 396.8 nm) exit at an angle j= 40°36", red ( l= 656.3 nm) - at an angle j= 42°22". In this angular interval D φ \u003d 1 ° 46 "encloses the entire spectrum of rays emerging from the drop. Violet rays form an inner cone, red ones form an outer cone. If the raindrops illuminated by the sun are seen by the observer, then those of them whose cone rays enter the eye are seen as the brightest. As a result, all drops that are in relation to the sun's ray passing through the observer's eye, at an angle of a red cone, are seen as red, at an angle of green - green (Fig. 209).

9. Secondary rainbow formation occurs due to the rays emerging from the drop after the second reflection (Fig. 210). The intensity of the rays after the second reflection is about an order of magnitude less than that of the rays after the first reflection and has approximately the same path with a change in uçR.

The rays emerging from the drop after the second reflection form a cone with an apex angle of ≈ 51º. If the primary cone has a smooth side on the outside, then the secondary cone has a smooth side on the inside. There are practically no rays between these cones. The larger the raindrops, the brighter the rainbow. With a decrease in the size of the droplets, the rainbow turns pale. When rain turns into drizzle R≈ 20 - 30 microns the rainbow degenerates into a whitish arc with almost indistinguishable colors.

10. Halo(from Greek. halōs- ring) - an optical phenomenon, which is usually iridescent circles around the disk of the sun or moon with an angular radius 22º and 46º. These circles are formed as a result of the refraction of light by ice crystals in cirrus clouds, which have the shape of hexagonal regular prisms.

Snowflakes falling to the ground are very diverse in shape. However, the crystals formed as a result of vapor condensation in the upper atmosphere are mainly in the form of hexagonal prisms. Of all the possible options for the passage of a beam through a hexagonal prism, three are most important (Fig. 211).

In case (a), the beam passes through opposite parallel faces of the prism without splitting or deflecting.

In case (b), the beam passes through the faces of the prism, which form an angle of 60º between them, and is refracted as in a spectral prism. The intensity of the beam emerging at the angle of least deviation of 22º is maximum. In the third case (c), the beam passes through the side face and base of the prism. Refractive angle 90º, angle of least deviation 46º. In the latter two cases, the white rays are split, the blue rays deviate more, the red rays less. Cases (b) and (c) cause the appearance of rings observed in the transmitted rays and having angular dimensions of 22º and 46º (Fig. 212).

Usually the outer ring (46º) is brighter than the inner one and both of them have a reddish tint. This is explained not only by the intense scattering of blue rays in the cloud, but also by the fact that the dispersion of blue rays in the prism is greater than that of red ones. Therefore, blue rays leave the crystals in a strongly divergent beam, due to which their intensity decreases. And the red rays come out in a narrow beam, which has a much greater intensity. Under favorable conditions, when it is possible to distinguish colors, the inside of the rings is red, the outside is blue.

10. crowns- bright foggy rings around the disk of the star. Their angular radius is much smaller than the halo radius and does not exceed 5º. Crowns arise due to diffraction scattering of rays by water droplets forming a cloud or fog.

If the drop radius R, then the first diffraction minimum in parallel beams is observed at an angle j = 0,61∙lçR(see formula 15.3). Here l is the wavelength of the light. The diffraction patterns of individual drops in parallel beams coincide; as a result, the intensity of the light rings is enhanced.

The diameter of the crowns can be used to determine the size of the droplets in the cloud. The larger the drops (more R), the smaller the angular size of the ring. The largest rings are observed from the smallest droplets. At distances of several kilometers, diffraction rings are still visible when the droplet size is at least 5 µm. In this case j max = 0.61 lçR≈ 5 ¸ 6°.

The color of the light rings of the crowns is very weak. When it is noticeable, the outer edge of the rings has a reddish color. That is, the distribution of colors in the crowns is inverse to the distribution of colors in the halo rings. In addition to the angular dimensions, this also makes it possible to distinguish between the crowns and the halo. If there are droplets of a wide range of sizes in the atmosphere, then the rings of the crowns, superimposed on each other, form a general bright glow around the star's disk. This glow is called halo.

11. Blue sky and scarlet dawn. When the Sun is above the horizon, a cloudless sky appears blue. The fact is that from the rays of the solar spectrum, in accordance with the Rayleigh law I rass ~ 1 /l 4, short blue, cyan and violet rays are scattered most intensively.

If the Sun is low above the horizon, then its disk is perceived as crimson red for the same reason. Due to the intense scattering of short-wavelength light, mainly weakly scattered red rays reach the observer. Scattering of rays from the rising or setting Sun is especially great because the rays travel a long distance near the surface of the Earth, where the concentration of scattering particles is especially high.

Morning or evening dawn - the coloring of the part of the sky close to the Sun in pink - is explained by the diffraction scattering of light on ice crystals in the upper atmosphere and the geometric reflection of light from crystals.

12. twinkling stars- These are rapid changes in the brightness and color of stars, especially noticeable near the horizon. The twinkling of stars is due to the refraction of rays in rapidly running jets of air, which, due to different densities, have a different refractive index. As a result, the layer of the atmosphere through which the beam passes behaves like a lens with a variable focal length. It can be both gathering and scattering. In the first case, the light is concentrated, the brilliance of the star is enhanced, in the second, the light is scattered. Such a sign change is recorded up to hundreds of times per second.

Due to dispersion, the beam is decomposed into rays of different colors, which follow different paths and can diverge the more, the lower the star is to the horizon. The distance between the violet and red rays from one star can reach 10 meters near the surface of the Earth. As a result, the observer sees a continuous change in the brightness and color of the star.

Optical phenomena in the atmosphere

The atmosphere is a complex mixture of gases. Molecules, atoms of gases, products of condensation and sublimation of water vapor, various solid particles suspended in the air participate in the process of light scattering. As a result, the atmosphere is a kind of optical system with constantly changing parameters. Optical phenomena in the atmosphere arise as a result of reflection,

refraction and dispersion(white light is decomposed into a spectrum),

atmosphere scattering halo refraction

diffraction ( deviation of a light wave from a rectilinear direction when passing through small holes or when bending around small obstacles) and interference(overlay) waves

The blue color of the sky is scientifically explained Rayleigh theory based on the law of molecular scattering. It states: "the intensity of the scattered light varies inversely with the fourth power of the wavelength of the light incident on the scattering particle." Since the wavelength of violet rays is half that of red rays, they scatter 16 times more. All other colored rays of the visible spectrum will be included in the scattered light in an amount inversely proportional to the fourth power of the wavelength of each of them. A mixture of all scattered rays gives a blue color.

Molecular Rayleigh scattering is a special case of aerosol dispersion. If the particle size exceeds 1/10 of the incident wavelength, then it passes into aerosol scattering Mie(whitish, reddish sky). At noon, predominantly long-wave rays reach the Sun - red, orange, yellow rays. When the Sun descends towards the horizon, the rays have to travel a longer path in the atmosphere. Losses of short-wavelength rays become noticeable. And the color of the Sun at sunset becomes orange or red.

The golden, orange or reddish hue of the sky above the horizon is called dawn. The color of the sky depends on the impurities of aerosols in the air. Golden hues indicate a small amount of aerosols in the air that scatter sunlight. The presence of water vapor increases the scattering of red rays in the atmosphere.

twilight rays- this phenomenon is due to the contrast between the light of the Sun, scattered water vapor in the air and the shadow cast by clouds located below the horizon or not high above the horizon.

Rainbow and halo- phenomena associated with the refraction and reflection of light rays in drops and crystals of clouds.

Rainbow observed in the direction opposite to the Sun, usually at a distance of 1-2 km from the observer. Sometimes it can be observed at a distance of several meters against the background of water drops. The center of the rainbow is on the same line with the eye of the observer and with the center of the solar disk. Refracted in a drop, the beam decomposes into primary colors. The inner color of the rainbow is purple, the outer color is red. The type of arc, the brightness of colors, the width of the stripes depend on the number, size and deformation of raindrops. Large drops create a narrower and brighter rainbow, small ones create an arc that is blurry, faded and even white.

The formation of the main rainbow (with an angular radius of about 42°) is explained by double refraction and single internal reflection sunlight to which they are exposed in water drops.

Often a second, less bright rainbow appears, with an angular radius of about 52° with the colors reversed. This rainbow is formed as a result double refraction and reflections rays in a drop. Much less often, weakly colored secondary arcs are observed on the inner side of the first rainbow.

Multiple forms halo can be divided into two main groups:

Halo, slightly tinged with iridescent colors. These are circles, arcs tangent to them, light spots (false suns);

Colorless halos are white. This is a horizontal circle, pillars and crosses.

The phenomenon of the first group is obtained as a result of the refraction of rays in ice crystals, and the phenomenon of the second group - as a result of reflection from their faces. These crystals are located between the observer and the light source in summer in the form of cirrus clouds, and in winter, also in the form of ice dust, haze or fog. The diversity of the halo depends on the shape of the ice crystals, their orientation, movement, and the height of the Sun above the horizon.

The most frequently observed halo with a radius of 22 °, the inner part of which is reddish, the outer part is bluish, the sky inside the ring seems darker. A 46° radius halo is a rarer occurrence. Due to its large size, this halo is extremely rarely observed as a full circle, usually only a part of it is visible. The iridescent color of the halo arises from the decomposition of a white light beam in an ice prism.

Even more rarely, complex halo shapes are observed when it consists of several circles, tangent and oblique arcs and false suns or moons. More often observed upper tangent-arcs to the halo at 22 and 46°. They are convexly turned to the sun, they are brightly colored, and the red color is turned to the Sun. They appear when there are crystals in the cloud with different arrangements of faces and refracting edges.

parhelic circle(or circle of false suns) - a white ring centered at the zenith point, passing through the Sun parallel to the horizon. This circle is the result of the reflection of the sun's rays from the side faces of hexagonal ice crystals floating in the air in a vertical position.

parhelia, or false suns, are brightly luminous spots * resembling the Sun, which are formed at the points of intersection of the parhelic * circle with the halo, having angular radii of 22 °, 46 ° and 90 °. Sometimes an antelium (anti-sun) is visible - a bright spot located on the parhelion ring exactly opposite the Sun. It is assumed that the cause of this phenomenon is the double internal reflection of sunlight. The reflected beam follows the same path as the incident beam, but in the opposite direction.

circumzenithal arc is an arc of 90° or less, centered on the zenith, approximately 46° above the Sun. It has bright colors, the outer side of the arc is painted red.

solar pole very common occurrence, reminiscent of sword. It arises as a result of the reflection of light rays from horizontal faces, ice plates floating in the air. Cross. This phenomenon is obtained as a result of the intersection of the pillars with a white horizontal circle.

3) Crowns, glories, Broken ghosts, halos, cloud iridescence arise as a result diffraction and interference sun rays.

crowns light, slightly colored rings, the inner side of which is blue, the outer side is red. They surround the Sun or the Moon, which shine through thin water clouds. The crown can be one adjacent to the luminary (halo), or several "additional rings" separated by gaps. Crowns are formed by extreme tangent rays incident on the surface of a spherical particle (cloud or fog droplets, dew, grains of sand). The reason for the appearance of crowns is the diffraction of light as it passes between the droplets and crystals of the cloud. Passing through small holes, the light beam goes around the edges of the droplet and at the same time decomposes into colored rays, which are deflected in different ways when the beam is bent at the edge of the hole. The dimensions of the crown depend on the size of the drops and crystals: the larger the drops (crystals), the smaller the crown, and vice versa. If cloud elements become larger in the cloud, the crown radius gradually decreases, and when the size of cloud elements decreases (evaporation), it increases.

When the rays pass inside the particle and at certain angles (tangents), the bulk of the rays are almost completely reflected and directed backward, almost parallel to the incident rays. These rays create a diffraction pattern in the opposite direction. So gloria also called "anti-crown" or "anti-corona". Broken Ghost formed in rough terrain when the sun is behind the observer around the shadow of a person falling on a vertical wall of fog. In the early morning, as soon as the sun rises, in a meadow abundantly covered with dew, a nimbus, it forms around the shadow of a person's head.

Sometimes during the day, separate parts of the clouds of cirrocumulus or altocumulus clouds glow with rainbow colors, and these colors shimmer like mother-of-pearl. The coloration is especially intense at the thin edges of the clouds. Cloud iridescence . The play of colors is obtained because the cloud moves and changes its density.

The optical phenomena observed in the atmosphere are closely related to the processes taking place in it, therefore crowns and halos are one of the main local signs of weather.

Phenomena astronomical and terrestrial refraction, due to the refraction of light rays in the atmosphere due to the uneven distribution of temperature and air density. refraction is called astronomical, if the light source is outside the atmosphere. Its consequences: the twinkling of stars, the distortion of the shape of the solar disk at sunrise and sunset, an increase in the length of the day. In middle latitudes (Moscow, St. Petersburg), due to refraction, the day usually increases by no more than 8-12 minutes, at the poles more. At sunset or sunrise, when the Sun is below the horizon, refraction raises it, and the day continues. The increase in the length of the day depends on the height of the luminary, on the latitude of the place of temperature and air pressure at the surface of the Earth.

Due to the refraction of the sun's rays, at sunrise and sunset the shape of the solar disk is distorted. The flattening of the Sun is explained by the fact that its lower edge, touching the horizon, experiences stronger refraction than the upper one. twinkling stars It is explained by the refraction and partial dispersion of the rays coming from the star in jets of either warm or cold air, which are constantly encountered in the path of its rays in the atmosphere.

Earth refraction arises as a result of the passage and refraction of rays from objects located inside the atmosphere in layers of air of different densities. The manifestation of terrestrial refraction is caused by large temperature gradients (more than 3°C per 100 m) in the atmosphere. In this case, distant objects may turn out to be raised or lowered relative to their actual position, and may also be distorted and acquire irregular, fantastic shapes. There are several types of mirages depending on where the image is located in relation to the subject: upper, lower, lateral and complex.

inferior mirage: It is formed as a result of the reflection of objects or the sky from the strongly heated air near the surface of the earth. They are observed in the steppes and deserts.

Superior mirage. They are formed as a result of the reflection of objects located beyond the horizon line from a warm layer of air located above a very cold surface of the Earth or the sea. Favorable conditions for them are created in the polar regions or over cold seas.

Side mirage. It occurs when air layers of the same density are located in the atmosphere not horizontally, but obliquely or even vertically. Such conditions are created in summer, in the morning after sunrise near the rocky shores of the sea or lake, when the shore is already illuminated by the Sun, and the surface of the water and air above it is still cold.

A complex type of mirage, or Fata Morgana, arise when conditions are simultaneously present for the appearance of both an upper and lower mirage, for example, with a significant temperature inversion at a certain height above warm water, a layer of cold air is formed. As a result of air flowing from the coastal mountains. Magic castles appear above the sea, changing, growing, disappearing.

Unusual atmospheric phenomena have inspired and continue to inspire fear in mystically inclined people. Therefore, in order to form an objective worldview in a student, these issues can be considered in optional classes. The study of the nature of optical phenomena will help explain the scientific foundations of physical processes, satisfy the cognitive interest of students in the study of selected areas of knowledge. Photos of phenomena can be used for demonstration purposes in geography lessons at school. Without a doubt, every student will be interested in expanding their knowledge in the field of studying optical phenomena in nature.

The vault of heaven made a lot of mysteries for a person, in the process of solving these problems, the same many new discoveries were made. A light beam, passing through the atmosphere of our planet, not only illuminates it, it gives it a unique look, making it beautiful.

The first attempt to explain the rainbow as a natural phenomenon was made in 1611 by Archbishop Antonio Dominis, for which he was excommunicated and sentenced to death, and his manuscripts were burned.

The scientific explanation of the rainbow was first given by René Descartes in 1637. Descartes built a picture for 10,000 rays. It turned out that with a single reflection, only a small group of rays (they are highlighted by solid lines) emerge from the drop in a compact beam, forming an angle of about 42° with the direction of the incident solar rays, and with a double reflection, 52°. All the rest (indicated by dotted lines) diverge in a wide fan, dissipate. In honor of the discoverer, this compact beam is called beam of Descartes.

Less than 5% of the energy of the solar flux falling on a drop is spent on a rainbow. At the same time, about 4% goes to the formation of the first rainbow.

Each person sees his own rainbow. Calculations showed that the rainbows of the 3rd, 4th, 7th and 8th internal reflections are located around the Sun, and the 5th, 6th - around the antisolar point. The angular dimensions of such rainbows can decrease to 30º 14º and 16º 51º. However, we hardly see them.

Rice. 5.

Various optical (light) phenomena in the atmosphere are due to the fact that the light rays of the sun and other celestial bodies, passing through the atmosphere, experience scattering and diffraction. In this regard, a number of amazingly beautiful optical phenomena occur in the atmosphere:

the color of the sky, the color of the dawn, twilight, the twinkling of stars, circles around the apparent location of the sun and moon, a rainbow, a mirage, etc. All of them, reflecting certain physical processes in the atmosphere, are very closely related to the change and state of the weather and therefore can add up as good local signs for her prediction.

As you know, the spectrum of sunlight consists of seven primary colors, red, orange, yellow, green, blue, indigo and violet. Various colors of white light rays are mixed in a strictly defined proportion. With any violation of this proportion, the light turns from white to colored. If rays of light fall on particles whose dimensions are smaller than the wavelengths of the rays, then, according to Rayleigh's law, they are scattered by these particles in inverse proportion to the wavelengths to the fourth power. These particles can be both molecules of gases that make up the atmosphere, and the smallest particles of dust.

The same particles scatter rays of different colors in different ways. Violet, blue and blue rays are scattered most strongly, red ones are weaker. That is why the sky is colored blue: at the horizon it has a light blue tone, and at the zenith it is almost blue.
Blue rays, passing through the atmosphere, are strongly scattered, while red rays reach the surface of the earth almost completely unscattered. This explains the red color of the solar disk at sunset or immediately after sunrise.

When light falls on particles whose diameter is almost equal to or greater than the wavelengths, then the rays of all colors are scattered equally. In this case, the scattered and incident light will be the same color.
Therefore, if larger particles are suspended in the atmosphere, then white will be added to the blue color of the sky, due to the scattering of gas molecules, and the sky will become blue with a whitish tint, increasing as the number of particles suspended in the atmosphere increases.
This color of the sky is observed when there is a lot of dust in the air.
The color of the sky becomes whitish, and if there are large amounts of condensation products of water vapor in the air in the form of water droplets, ice crystals, the sky acquires a reddish and orange tint.
This phenomenon is usually observed during the passage of fronts or cyclones, when moisture is carried high up by powerful air currents.

When the sun is near the horizon, the rays of light have to travel a long way to the surface of the earth in a layer of air, often containing a large amount of large particles of moisture and dust. In this case, blue light is scattered very weakly, red and other rays are more strongly scattered, coloring the lower layer of the atmosphere in various bright and brown shades of red, yellow and other colors, depending on the dust content, humidity and dryness of the air.

Closely related to the color of the sky is a phenomenon called opalescent haze. The phenomenon of opalescent turbidity of the air consists in the fact that distant earthly objects seem to be shrouded in a bluish haze (scattered violet, blue, blue colors).
This phenomenon is observed in those cases when the air is in a suspended state (a lot of tiny dust particles with a diameter of less than 4 microns.

Numerous studies of the color of the sky using a special device (cyanometer) and visually established the relationship between the color of the sky and the nature of the air mass. It turned out that there is a direct relationship between these two phenomena.
Deep blue color indicates the presence of an arctic air mass in the area, and whitish - dusty continental and tropical. When, as a result of the condensation of water vapor in the air, particles of water or ice crystals larger than air molecules are formed, they reflect all the rays equally, and the sky becomes whitish or grayish in color.

Solid and liquid particles in the atmosphere cause significant haze in the air and therefore greatly reduce visibility. The visibility range in meteorology is understood as the limiting distance at which, under a given state of the atmosphere, the objects under consideration cease to be distinguishable.

Therefore, the color of the sky and visibility, which depend largely on the size of particles in the air, make it possible to judge the state of the atmosphere and the upcoming weather.

A number of local signs of weather prediction are based on this:

Dark bluish skies during the day (only near the sun can be slightly whitish), moderate to good visibility, and calm weather result in little water vapor in the troposphere, so anticyclone weather can be expected to last 12 hours or more.

A whitish sky during the day, average or poor visibility indicate the presence of a large amount of water vapor, condensation products and dust in the troposphere, i.e., the periphery of the anticyclone passes here, in contact with the cyclone: ​​we can expect a transition to cyclonic weather in the next 6-12 hours.

The color of the sky, which has a greenish tint, indicates the great dryness of the air in the troposphere; In summer, it portends hot weather, and in winter, frosty.

An even gray sky in the morning precedes clear good weather, a gray evening and a red morning precede stormy windy weather.

The whitish hue of the sky near the horizon at low altitude (while the rest of the sky is blue) has a slight dampness in the troposphere and portends good weather.

A gradual decrease in the brightness and blueness of the sky, an increase in a whitish spot near the sun, clouding of the sky near the horizon, deterioration in visibility are a sign of the approach of a warm front or a warm-type occlusion front.

If distant objects are clearly visible and do not seem closer than they really are, anticyclonic weather can be expected.

If distant objects are clearly visible, but the distance to them seems closer than the actual one, then there is a large amount of water vapor in the atmosphere: you need to wait for the weather to worsen.

Poor visibility of distant objects on the coast indicates the presence of a large amount of dust in the lower air layer and is a sign that precipitation should not be expected in the next 6-12 hours.

High air transparency with a visibility range of 20-50 km or more is a sign of the presence of an arctic air mass in the area

The clear visibility of the moon with an apparent bulging disk indicates high air humidity in the troposphere and is a sign of worsening weather.

A well-visible ashy moonlight portends bad weather. Ash light is a phenomenon when, in the first days after the new moon, in addition to the narrow bright crescent of the moon, its entire full disk is visible, dimly illuminated by light reflected from the earth.

Dawn

Dawn is the color of the sky at sunrise and sunset.

The variety of colors of dawn is caused by different conditions of the atmosphere. The colored stripes of dawn, counting from the horizon, are always observed in the order of the colors of the spectrum red, orange, yellow, blue.
Individual colors may be completely absent, but the order of distribution never changes. The horizon below red may sometimes have a gray dirty purple that appears lilac. The upper part of the dawn is either whitish or blue.

The main factors affecting the appearance of dawn are the products of water vapor condensation and dust contained in the atmosphere:

The more moisture in the air, the more pronounced the red color of the dawn. An increase in air humidity is usually observed before the approach of a cyclone, a front that brings inclement weather. Therefore, with bright red and orange dawns, wet weather with strong winds can be expected. The predominance of yellow (golden) tones of dawn indicates a small amount of moisture and a large amount of dust in the air, which indicates the upcoming dry and windy weather.

Bright and purple-red dawns, similar to the glow of a distant fire with cloudy hues, indicate high air humidity and are a sign of worsening weather - the approach of a cyclone, a front in the next 6-12 hours.

The predominance of bright yellow, as well as golden and pink tones of the evening dawn, indicates a low humidity of the air; dry, often windy weather can be expected.

Light red (pink) sky in the evening indicates light windy weather without precipitation.

A ruddy evening and a gray morning portend a clear day and an evening with light winds.

The more tender the red color of the clouds at evening dawn, the more favorable the upcoming weather will be.

A yellowish-brown dawn in winter during frost indicates their persistence and possible intensification.

A cloudy yellowish pink evening dawn is a sign of a likely deterioration in the weather.

If the sun, approaching the horizon, little changes its usual whitish-yellow color and sets very bright, which is due to the high transparency of the atmosphere, low moisture and dust content, then good weather will continue.

If the sun, before setting to the horizon, or at sunrise at the moment when its edge appears, gives a flash of a bright green ray, then we must expect the preservation of stable, clear, calm weather; if you managed to notice a blue beam at the same time, then you can expect it. Especially quiet and clear weather. The duration of the flash of the green beam is no more than 1-3 seconds.

The predominance of greenish shades during the evening dawn indicates a long dry clear weather.

A light silvery strip without any sharp boundaries, visible for a long time at the horizon in a cloudless sky after sunset, portends a long calm anticyclonal weather.

The gentle pink illumination of motionless cirrus clouds during the setting of the salt in the absence of other clouds is a reliable sign of established anticyclonic weather.

The predominance of a bright red color in the evening dawn, which persists for a long time as the sun further sinks below the horizon, is a sign of the approach of a warm front or a warm-type occlusion front; one should expect prolonged inclement windy weather.

A gently pink dawn in the form of a circle above the sun that has set beyond the horizon is good stable weather. If the color of the circle turns pink-red, precipitation and increased wind are possible.

The color of the dawn is closely related to the nature of the air mass. The table compiled for the temperate latitudes of the European part of the CIS shows the relationship between the colors of dawn and air masses according to N. I. Kucherov:

Sunset

Since cyclones move mainly from the western points, the appearance of clouds in the western half of the sky is usually a sign of the approach of a cyclone, and if this happens in the evening, then the sun sets into the clouds. But at the same time, it is necessary to take into account the sequence of cloud forms, which is associated with cyclones, atmospheric fronts.

If the sun sets behind a low solid cloud that stands out sharply against the background of a greenish or yellowish sky, then this is a sign of upcoming good (dry, calm and clear) weather.

If the sun sets with continuous low cloudiness and if layers of cirrus or cirrostratus clouds are observed on the horizon and above the cloudiness, then precipitation will fall, windy cyclonic weather will occur in the next 6-12 hours.

Sunset behind dark dense clouds with a red color at the edges heralds cyclonic weather.

If, after sunset, a dark cone gradually spreading upwards with a wide blurred orange border is clearly visible in the east - the shadow of the earth, then a cyclone is approaching from the sunset side.

The shadow of the earth in the east after sunset is grey-gray, with no edge color or with a pale pink color - a sign of the persistence of anticyclonic weather.

This is the name given to a beam of individual light rays or bands coming out from behind the clouds covering the sun. The rays of the sun pass through the gaps between the clouds, illuminate the water droplets floating in the air in suspension, and give a bunch of light bands in the form of ribbons (Buddha rays).

Since this radiance is observed due to the presence of a large number of small water droplets in the air, it portends rainy, windy cyclonic weather.

The radiance emerging from behind a dark cloud, behind which the sun is located, is a sign of the onset of windy weather with rain in the next 3-6 hours.

The radiance due to yellow clouds, observed immediately after the last rain, portends the imminent resumption of rain and increased wind.

The red color of the sun, moon and other celestial bodies indicates a high humidity in the atmosphere, i.e. establishment in the next 6-10 hours of cyclonic weather with strong winds and precipitation.

The reddish color of the darkened disk of the sun, together with the bluish color of distant objects (mountains, etc.) is a sign of the spread of dusty tropical air, and a significant increase in air temperature should be expected soon.

Observing the vault of heaven from an open place (for example, in the sea), you can see that it has the shape of a hemisphere, but flattened in the vertical direction. It often seems that the distance from the observer to the horizon is three to four times greater than to the zenith.

This is explained as follows. When looking up, without tilting the head back, objects appear to us shortened compared to those that are in a horizontal position.

For example, fallen poles or trees appear longer than vertical ones. In the horizontal direction, atmospheric perspective acts, due to which objects shrouded in haze (from dust and ascending currents) seem less illuminated and therefore more distant.

The apparent oblateness of the firmament varies depending on the weather conditions. Great transparency of the atmosphere and high humidity increase the flattening of the sky.

A flattened, low vault of heaven is seen before cyclonic weather.

A high vault of heaven is observed in the central regions of anticyclones; it can be expected that good anticyclonic weather will persist for 12 hours or more.

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

This circumstance gives rise to a whole a number of optical phenomena in the atmosphere due to 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 air density (and hence the refractive index) decreases. Imagine that the atmosphere consists of optically homogeneous horizontal layers, the refractive index in 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, it will, in accordance with the law of refraction, “press” against the perpendicular to the layer boundary. But the density of the atmosphere does not decrease in jumps, but continuously, which leads to a smooth curvature and rotation of the beam through an angle α when passing through the atmosphere.

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

For the same reason, the duration of the day increases (in our latitudes by 10-12 minutes), the disks of the Moon and the Sun near the horizon are compressed. Interestingly, the maximum refraction angle 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 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 associated with the astronomical refraction of light. It has long been noted that twinkling is most noticeable in stars near the horizon. Air currents in the atmosphere change the density of the air over time, resulting in an apparent twinkling of the heavenly body. Astronauts in orbit do not observe any flicker.

Mirages

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

Sometimes this phenomenon is called terrestrial refraction. The appearance 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 on it, which in fact are not. In this case, we take for "puddles" the specular reflection of rays from non-uniformly heated layers of air located in the immediate vicinity of the "hot" asphalt.

superior mirages differ in considerable variety: in some cases they give a direct image (Fig. 301, a), in others they are inverted (Fig. 301, b), they can be double and even triple. These features are associated with different dependences of air temperature and refractive index on altitude.

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. So, during the rain, education is an amazing and unforgettable sight. rainbows, which is explained by the phenomenon of different refraction (dispersion) and reflection of sunlight 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 mutually inverse.

The light beam involved in the formation of a rainbow experiences 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) must be between the Sun and the 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 is scattered 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 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 the 11th grade. general education institutions with Russian. lang. training with a 12-year term of study (basic and advanced) / V.V. Zhilko, L.G. Markovich. - Minsk: Nar. Asveta, 2008. - S. 334-337.

The variety of optical phenomena in the atmosphere is due to various reasons. The most common phenomena include lightning and very picturesque northern and southern auroras. In addition, the rainbow, halo, parhelion (false sun) and arcs, crown, halos and ghosts of Brocken, mirages, St. Elmo's fires, luminous clouds, green and twilight rays are of particular interest. Rainbow is the most beautiful atmospheric phenomenon. Usually this is a huge arch, consisting of multi-colored stripes, observed when the Sun illuminates only part of the sky, and the air is saturated with water droplets, for example, during rain. The multi-colored arcs are arranged in a spectrum sequence (red, orange, yellow, green, cyan, indigo, violet), but the colors are almost never pure because the bands overlap. As a rule, the physical characteristics of rainbows vary significantly, and therefore they are very diverse in appearance. Their common feature is that the center of the arc is always located on a straight line drawn from the Sun to the observer. The lava rainbow is an arc consisting of the brightest colors - red on the outside and purple on the inside. Sometimes only one arc is visible, but often a secondary one appears on the outside of the main rainbow. It has not as bright colors as the first one, and the red and purple stripes in it change places: red is located on the inside.

The formation of the main rainbow is explained by double refraction and single internal reflection of the rays of sunlight. Penetrating inside a drop of water (A), a ray of light is refracted and decomposed, as when passing through a prism. Then it reaches the opposite surface of the drop, is reflected from it, and exits the drop to the outside. In this case, the beam of light, before reaching the observer, is refracted a second time. The initial white beam is decomposed into rays of different colors with a divergence angle of 2°. When a side rainbow is formed, double refraction and double reflection of the sun's rays occur. In this case, the light is refracted, penetrating inside the drop through its lower part, and is reflected from the inner surface of the drop, first at point B, then at point C. At point D, the light is refracted, leaving the drop towards the observer. When rain or mist forms a rainbow, the full optical effect is achieved by the combined effect of all the water droplets crossing the surface of the rainbow's cone with the observer at the apex. The role of each drop is fleeting. The surface of the rainbow cone consists of several layers. Quickly crossing them and passing through a series of critical points, each drop instantly decomposes the sun's ray into the entire spectrum in a strictly defined sequence - from red to purple. Many drops cross the surface of the cone in the same way, so that the rainbow appears to the observer as continuous both along and across its arc. Halo - white or iridescent light arcs and circles around the disk of the Sun or Moon. They are caused by the refraction or reflection of light by ice or snow crystals in the atmosphere. The crystals that form the halo are located on the surface of an imaginary cone with the axis directed from the observer (from the top of the cone) to the Sun. Under certain conditions, the atmosphere is saturated with small crystals, many of whose faces form a right angle with the plane passing through the Sun, the observer, and these crystals. Such facets reflect incoming light rays with a deviation of 22°, forming a halo that is reddish on the inside, but it can also consist of all colors of the spectrum. Less common is a halo with an angular radius of 46°, located concentrically around a 22° halo. Its inner side also has a reddish tint. The reason for this is also the refraction of light, which occurs in this case on the crystal faces that form right angles. The width of the ring of such a halo exceeds 2.5?. 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 that has a common center with the other two halos. If it is colored, it has a red color on the outside of the ring. The mechanism of the origin of this type of halo has not been fully elucidated. Parhelia and arcs. Parhelic circle (or circle of false suns) - a white ring centered at the zenith point, passing through the Sun parallel to the horizon. The reason for its formation is the reflection of sunlight from the edges of the surfaces of ice crystals. If the crystals are sufficiently evenly distributed in the air, a full circle becomes visible. Parhelia, or false suns, are brightly luminous spots resembling the Sun, which are formed at the points of intersection of the parhelic circle with the halo, having angular radii of 22?, 46? and 90?. The most frequently formed and brightest parhelion forms at the intersection with a 22-degree halo, usually colored in almost all colors of the rainbow. False suns at intersections with 46- and 90-degree halos are observed much less frequently. Parhelia that occur at intersections with 90-degree halos are called paranthelia, or false countersuns. Sometimes an antelium (counter-sun) is also visible - a bright spot located on the parhelion ring exactly opposite the Sun. It is assumed that the cause of this phenomenon is the double internal reflection of sunlight. The reflected beam follows the same path as the incident beam, but in the opposite direction. The circumzenithal arc, sometimes incorrectly called the upper tangent arc of the 46-degree halo, is the 90? or less, centered on the zenith, about 46° above the Sun. It is rarely visible and only for a few minutes, has bright colors, and the red color is confined to the outer side of the arc. The circumzenithal arc is notable for its coloration, brightness, and clear outlines. Another curious and very rare optical effect of the halo type is the Lovitz arc. They arise as a continuation of parhelia at the intersection with the 22-degree halo, pass from the outer side of the halo and are slightly concave towards the Sun. Pillars of whitish light, as well as various crosses, are sometimes visible at dawn or dusk, especially in the polar regions, and can accompany both the Sun and the Moon. At times, lunar halos and other effects similar to those described above are observed, with the most common lunar halo (ring around the Moon) having an angular radius of 22?. Like false suns, false moons can arise. Crowns, or crowns, are small concentric colored rings around the Sun, Moon or other bright objects that are observed from time to time when the light source is behind translucent clouds. The corona radius is smaller than the halo radius and is approx. 1-5?, the blue or purple ring is closest to the Sun. A corona is formed when light is scattered by small water droplets of water that form a cloud. Sometimes the crown looks like a luminous spot (or halo) surrounding the Sun (or Moon), which ends with a reddish ring. In other cases, at least two concentric rings of larger diameter, very weakly colored, are visible outside the halo. This phenomenon is accompanied by iridescent clouds. Sometimes the edges of very high clouds are painted in bright colors. Gloria (halos). Under special conditions, unusual atmospheric phenomena occur. If the Sun is behind the observer, and its shadow is projected onto nearby clouds or a curtain of fog, under a certain state of the atmosphere around the shadow of a person's head, you can see a colored luminous circle - a halo. Usually such a halo is formed due to the reflection of light by dew drops on a grassy lawn. Glorias are also quite common to be found around the shadow that the plane casts on the underlying clouds. Ghosts of the Brocken. In some regions of the globe, when the shadow of an observer 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 is due to the reflection and refraction of light by the smallest water droplets in the fog. The described phenomenon is called the "ghost of the Brocken" after the peak in the Harz mountains in Germany. Mirages are an optical effect caused by the refraction of light when passing through layers of air of different densities and is expressed in the appearance of a virtual image. In this case, distant objects may turn out to be raised or lowered relative to their actual position, and may also be distorted and acquire irregular, fantastic shapes. Mirages are often observed in hot climates, such as over sandy plains. Inferior mirages are common, when the distant, almost flat desert surface takes on the appearance of open water, especially when viewed from a slight elevation or simply above a layer of heated air. A similar illusion usually occurs on a heated paved road that looks like a water surface far ahead. In reality, this surface is a reflection of the sky. Below eye level, objects, usually upside down, may appear in this "water". An “air puff cake” is formed above the heated land surface, and the layer closest to the earth is the most heated and so rarefied that light waves passing through it are distorted, since their propagation speed varies depending on the density of the medium. Superior mirages are less common and more scenic than inferior mirages. Distant objects (often below the sea horizon) appear upside down in the sky, and sometimes a direct image of the same object also appears above. This phenomenon is typical for cold regions, especially when there is a significant temperature inversion, when a warmer layer of air is above the colder layer. This optical effect is manifested as a result of complex patterns of propagation of the front of light waves in air layers with a non-uniform density. Very unusual mirages occur from time to time, especially in the polar regions. When mirages occur on land, trees and other landscape components are upside down. In all cases, objects in the upper mirages are more clearly visible than in the lower ones. When the boundary of two air masses is a vertical plane, side mirages are sometimes observed. Saint Elmo's fire. Some optical phenomena in the atmosphere (for example, glow and the most common meteorological phenomenon - lightning) are electrical in nature. Much less common are the fires of St. Elmo - 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 the yards of ships at sea. Sometimes it seems that the entire rigging of the ship is covered with phosphorus and glows. Elmo's fires sometimes appear on mountain peaks, as well as on spiers and sharp corners of tall buildings. This phenomenon is brush electrical discharges at the ends of electrical conductors, when the electric field strength is greatly increased in the atmosphere around them. Will-o'-the-wisps are a faint bluish or greenish glow that is sometimes seen in swamps, cemeteries, and crypts. They often appear as a calmly burning, non-heating, candle flame raised about 30 cm above the ground, hovering over the object for a moment. The light seems to be completely elusive and, as the observer approaches, it seems to move to another place. The reason for this phenomenon is the decomposition of organic residues and the spontaneous combustion of marsh gas methane (CH 4) or phosphine (PH 3). Wandering lights have a different shape, sometimes even spherical. Green beam - a flash of emerald green sunlight at the moment when the last ray of the Sun disappears below the horizon. The red component of sunlight disappears first, all the others follow in order, and the emerald green remains last. This phenomenon occurs only when only the very edge of the solar disk remains above the horizon, otherwise there is a mixture of colors. Crepuscular rays are diverging beams of sunlight that become visible when they illuminate dust in the high atmosphere. Shadows from the clouds form dark bands, and rays propagate between them. This effect occurs when the Sun is low on the horizon before dawn or after sunset.