The variety of optical phenomena in the atmosphere is due to for various reasons. The most common phenomena include lightning and the very picturesque northern and southern auroras. In addition, the rainbow, halo, parhelium (false sun) and arcs, corona, halos and Brocken ghosts, mirages, St. Elmo's fire, luminous clouds, green and crepuscular rays are especially interesting. 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 spectral sequence (red, orange, yellow, green, blue, indigo, violet), but the colors are almost never pure because the stripes overlap each other. As a rule, the physical characteristics of rainbows vary significantly, and therefore appearance they are very diverse. Their common feature is that the center of the arc is always located on a straight line drawn from the Sun to the observer. a lava rainbow is an arc consisting of the most bright colors- red on the outside and purple on the inside. Sometimes only one arc is visible, but often with outside The main rainbow appears as a secondary one. It has not as bright colors as the first one, and the red and purple stripes in it change places: the red one is located with inside.
The formation of the main rainbow is explained by double refraction and single internal reflection of sunlight rays. Penetrating inside a drop of water (A), a ray of light is refracted and decomposed, as if passing through a prism. Then it reaches the opposite surface of the drop, is reflected from it and leaves the drop outside. In this case, the light ray is refracted a second time before reaching the observer. The original white beam is decomposed into rays different colors with a divergence angle of 2?. When a secondary rainbow is formed, double refraction and double reflection of the sun's rays occur. In this case, light is refracted, penetrating into the drop through its lower part, and reflected from inner surface drops first at point B, then at point C. At point D, the light is refracted, leaving the drop towards the observer. When rain or spray forms a rainbow, the full optical effect is achieved by the combined effect of all the water droplets crossing the surface of the rainbow cone with the observer at the apex. The role of every 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 intersect 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. Halos are white or iridescent light arcs and circles around the disk of the Sun or Moon. They arise due to 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 an axis directed from the observer (from the top of the cone) to the Sun. Under certain conditions, the atmosphere can be 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 faces 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 edges of the crystals forming 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 shares a common center with two other halos. If it is colored, it will have a red color on the outside of the ring. The mechanism by which this type of halo appears is not fully understood. Parhelia and arcs. The parhelic circle (or circle of false suns) is 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 complete circle becomes visible. Parhelia, or false suns, are brightly luminous spots reminiscent of the Sun, which are formed at the points of intersection of the parhelic circle with a halo having angular radii of 22?, 46? and 90?. The most frequently occurring and brightest parhelium forms at the intersection with the 22-degree halo, usually colored in almost every color 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 (anti-sun) is also visible - a bright spot located on the parhelium ring exactly opposite the Sun. It is assumed that the cause of this phenomenon is the double internal reflection of sunlight. The reflected ray follows the same path as the incident ray, but in the opposite direction. The near-zenith arc, sometimes incorrectly called the upper tangent arc of the 46-degree halo, is an arc of 90? or less, centered at the zenith point, located approximately 46° above the Sun. It is rarely visible and only for a few minutes, has bright colors, with the red color confined to the outer side of the arc. The near-zenith arc is remarkable for its color, brightness and clear outlines. Another interesting and very rare optical effect of the halo type is the Lowitz arc. They arise as a continuation of the parhelia at the intersection with the 22-degree halo, extend from the outer side of the halo and are slightly concave towards the Sun. Columns of whitish light, like 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 (a ring around the Moon) having an angular radius of 22?. Just like false suns, false moons can arise. Coronas, or crowns, are small concentric rings of color around the Sun, Moon or other bright objects that are observed from time to time when the light source is behind translucent clouds. The radius of the corona is less than the radius of the halo and is approx. 1-5?, the blue or violet ring is closest to the Sun. 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. In other cases, at least two concentric rings of larger diameter, very faintly colored, are visible outside the halo. This phenomenon is accompanied by rainbow clouds. Sometimes the edges of very high clouds have bright colors. Gloria (halos). Under special conditions, unusual atmospheric phenomena. 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. Typically, such a halo is formed due to the reflection of light from dew drops on a grassy lawn. Glorias are also quite often found around the shadow cast by the aircraft on the underlying clouds. Ghosts of Brocken. In some areas of the globe, when the shadow of an observer located on a hill at sunrise or sunset falls behind him on clouds located at a short distance, a striking effect is discovered: the shadow takes on colossal dimensions. This occurs due to the reflection and refraction of light by tiny water droplets in the fog. The described phenomenon is called the “Ghost of 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 expressed in the appearance of a virtual image. In this case, distant objects may appear 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 distant, almost flat surface The desert takes on the appearance of open water, especially if viewed from a small elevation or simply located above a layer of heated air. This illusion usually occurs on a heated asphalt road, which looks like a water surface far ahead. In reality, this surface is a reflection of the sky. Below eye level, objects may appear in this “water,” usually upside down. An “air” is formed over the heated land surface. layer cake“, and the layer closest to the ground is the hottest and is so rarefied that light waves passing through it are distorted, since the speed of their propagation changes depending on the density of the medium. The upper mirages are less common and more picturesque than the lower ones. Distant objects (often located beyond the sea horizon) appear upside down in the sky, and sometimes an upright image of the same object also appears above. This phenomenon is typical in cold regions, especially when there is a significant temperature inversion, when there is a warmer layer of air above a colder layer. This optical effect manifests itself as a result of complex patterns of propagation of the front of light waves in layers of air with inhomogeneous 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 are visible more clearly in the upper mirages than in the lower ones. When the boundary of two air masses is a vertical plane, lateral mirages are sometimes observed. St. 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 St. Elmo's lights - luminous pale blue or purple brushes from 30 cm to 1 m or more in length, usually on the tops of masts or the ends of yards of ships at sea. Sometimes it seems that the entire rigging of the ship is covered with phosphorus and glows. St. Elmo's Fire sometimes appears on mountain peaks, as well as on the spiers and sharp corners of tall buildings. This phenomenon represents brush electrical discharges at the ends of electrical conductors when the tension in the atmosphere around them greatly increases electric field. Will-o'-the-wisps are a faint bluish or greenish glow that is sometimes observed in swamps, cemeteries and crypts. They often look like a candle flame raised about 30 cm above the ground, quietly burning, giving no heat, and hovering for a moment over the object. The light seems completely elusive and, when 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 swamp gas methane (CH 4) or phosphine (PH 3). Will-o'-the-wisps have different shapes, sometimes even spherical. Green ray - a flash of emerald green sunlight at the moment when the last ray of the Sun disappears behind the horizon. The red component of sunlight disappears first, all the others follow in order, and the last one remains is emerald green. This phenomenon occurs only when only the very edge of the solar disk remains above the horizon, otherwise a mixture of colors occurs. 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 dawn or after sunset.
In ancient times, mirages, auroras, mysterious glowing lights and ball lightning frightened superstitious people. Today scientists have managed to uncover the secrets of these mysterious phenomena, understand the nature of their occurrence.
Phenomena associated with the reflection of sunlight
Everyone has seen many times how, after rain or near a stormy water stream, a colored bridge appears in the sky - a rainbow. The rainbow owes its colors to the sun's rays and droplets of moisture suspended in the air. When light hits a drop of water, it seems to split into various colors. In most cases, the drop reflects light only once, but sometimes light reflects off the drop twice. Then two rainbows flash in the sky.
Many desert travelers have witnessed another atmospheric phenomenon, the mirage. In the middle of the desert, an oasis with palm trees appeared, a caravan or ship moving across the sky. This happens when hot air above the surface rises. Its density begins to increase with height. Then the image of a distant object can be seen above its actual position.
In frosty weather, pronounced halo rings appear around the Sun and Lupus. They form when light is reflected by ice crystals that are quite high in the atmosphere, such as cirrus clouds. On the inside, the halo may have a bright color and a reddish tint. Ice crystals sometimes reflect so bizarrely sunlight that other illusions appear in the sky: two suns, vertical pillars of light or solar arcs. Around the Sun and Moon, halos sometimes form - crowns. The crowns look like several rings nested inside each other. They occur in altocumulus and altostratus clouds. A crown of color may appear around a shadow cast, for example, by an airplane on the underlying clouds.
Phenomena related to electricity
Tiny particles from space often fall into the upper layers. Due to their collision with particles of gases and dust, the aurora appears - a glow of the sky with flashes in the polar latitudes of the Northern and Southern Hemispheres. The shapes and colors of the aurora are varied. Its duration can range from tens of minutes to several days.
Drops and ice crystals moving in cumulonimbus clouds accumulate electrical charges. This causes a giant spark to appear between the clouds or between the cloud and the ground - lightning, which is accompanied by thunder. The accumulation of electricity in the atmosphere sometimes forms a luminous ball with a diameter of tens of centimeters - this is ball lightning. It moves with the movement of air and can explode upon contact with individual objects, especially metal ones. Having penetrated the house, ball lightning quickly moves through the room, leaving behind scorched areas. Ball lightning can cause serious burns and death. An exact explanation of the nature of this phenomenon does not yet exist.
Another phenomenon associated with the electric glow of the atmosphere is St. Elmo's fire. This glow can be observed in thunderstorms on high tower spiers, as well as around ship masts. It frightened superstitious sailors, who considered it a bad sign.
Prepared by a student of grade 11 “B”
Lukyanenko Anastasia
Optical phenomena in the atmosphere
Mirages
There are three classes of mirages. The first class is the lower mirages. With this type of mirage, bottom part deserts, i.e. a small strip of sand optically turns into a kind of pond. This can be seen if it is a level above this band. Such mirages are the most common. The second type of mirages is superior mirages. This is a rarer phenomenon, and also less picturesque. Superior mirages appear at great distances and at great heights above the horizon. The third class of mirages defies any explanation, and for many years scientists have been puzzling over the solution to this mystery.
What is the reason for the appearance of such amazing phenomena? This happens thanks to the amazing plays of light and air. Here's how to understand it. When the air temperature is quite high, and it is higher at the surface of the earth than in higher layers, favorable conditions for the occurrence of mirages. The density of air decreases as its temperature increases, and vice versa. And, as you know, the denser the air, the better it refracts light. The rays falling from the sky have a blue spectrum, and some of them are refracted, while others reach human vision and form the overall picture of the visible sky. That part of the rays that is refracted reaches the ground in front of the person, and, refracting on its surface, also falls into the person’s field of vision. We see these rays in the blue spectrum, which is why it seems that there is a blue body of water ahead of us. This impression is reinforced by the heated air oscillating in front of us.
If a mirage appears above the surface of the sea, then everything happens exactly the opposite. Below, above the surface of the water, the air temperature is lower, and with height it is higher. With this combination of circumstances, upper mirages arise, in which we observe the image of one or another object in the sky.
Rainbow.
Rainbow is a beautiful celestial phenomenon that has always attracted human attention. In earlier times, when people still knew very little about the world around them, the rainbow was considered a “heavenly sign.” So, the ancient Greeks thought that a hundred rainbows were the smile of the goddess Iris. A rainbow is observed in the direction opposite to the Sun, against the background of rain clouds or rain. A multi-colored arc is usually located at a distance of 1-2 km from the observer, 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.
Parhelia.
"Parhelium" translated from Greek means "false sun." This is a form of halo in the sky where one or more additional images of the Sun are observed, located at the same height above the horizon as the real Sun. Millions of ice crystals with vertical surface, reflecting the Sun, and form this beautiful phenomenon.
Parhelia can be observed in calm weather with a low position of the Sun, when a significant number of prisms are located in the air so that their main axes are vertical, and the prisms slowly descend like small parachutes. In this case, the brightest refracted light enters the eye at an angle of 220 from the faces located vertically, and creates vertical pillars on both sides of the Sun along the horizon. These pillars can be particularly bright in some places, giving the impression of a false Sun.
Auroras
One of the most beautiful optical phenomena of nature is the aurora. It is impossible to convey in words the beauty of the auroras, iridescent, flickering, flaming against the background of the dark night sky in the polar latitudes.
In most cases, auroras have a green or blue-green hue with occasional spots or a border of pink or red.
The aurora is visible from space. And it’s not just visible, but visible much better than from the surface of the Earth, since in space, neither the sun, nor clouds, nor the distorting influence of the lower dense layers of the atmosphere interfere with observing the aurora. According to the astronaut, from the ISS orbit, the auroras look like huge green constantly moving amoebas.
The aurora can last for days. Or maybe just a few tens of minutes.
The aurora can be observed not only on Earth. It is believed that the atmospheres of other planets (for example, Venus) also have the ability to generate auroras. The nature of the auroras on Jupiter and Saturn, according to the latest scientific data, is similar to the nature of their terrestrial counterparts.
A person constantly encounters light phenomena. Everything that is associated with the emergence of light, its propagation and interaction with matter is called light phenomena. Vivid examples optical phenomena can be: a rainbow after rain, lightning during a thunderstorm, the twinkling of stars in the night sky, the play of light in a stream of water, the variability of the ocean and sky, and many others.
Schoolchildren receive a scientific explanation of physical phenomena and optical examples in 7th grade, when they start studying physics. For many, optics will become the most fascinating and mysterious section in the school physics curriculum.
What does a person see?
Human eyes are designed in such a way that he can only perceive the colors of the rainbow. Today it is already known that the spectrum of the rainbow is not limited to red on one side and violet on the other. After red comes infrared, after violet comes ultraviolet. Many animals and insects are able to see these colors, but people, unfortunately, cannot. But a person can create devices that receive and emit light waves of the appropriate length.
Refraction of rays
Visible light is a rainbow of colors, and light white, for example, sunny, is a simple combination of these colors. If you place a prism in a beam of bright white light, it will break down into the colors or wavelengths of which it is composed. Red with a longer wavelength will appear first, then orange, yellow, green, blue and finally violet, which has the shortest wavelength in visible light.
If you take another prism to catch the light of the rainbow and turn it upside down, it will merge all the colors into white. There are many examples of optical phenomena in physics; let’s consider some of them.
Why is the sky blue?
Young parents are often perplexed by the simplest, at first glance, questions of their little whys. Sometimes they are the hardest to answer. Almost all examples of optical phenomena in nature can be explained by modern science.
The sunlight that illuminates the sky during the day is white, which means, in theory, the sky should also be bright white. In order for it to look blue, some processes are necessary with the light as it passes through the Earth's atmosphere. Here's what happens: Some of the light passes through the free space between gas molecules in the atmosphere, reaching the earth's surface and remaining the same white color as when it started. But sunlight encounters gas molecules, which, like oxygen, are absorbed and then scattered in all directions.
The atoms in the gas molecules are activated by the light they absorb and again emit photons of light in wavelengths ranging from red to violet. Thus, some of the light is directed towards the earth, the rest is sent back to the Sun. The brightness of the emitted light depends on the color. Eight photons of blue light are released for every photon of red light. Therefore, blue light is eight times brighter than red. Intense blue light is emitted from all directions from billions of gas molecules and reaches our eyes.
Multicolored arch
Once upon a time, people thought that rainbows were signs sent to them by the gods. Indeed, beautiful multi-colored ribbons always appear in the sky out of nowhere, and then just as mysteriously disappear. Today we know that a rainbow is one of the examples of optical phenomena in physics, but we never cease to admire it every time we see it in the sky. The interesting thing is that each observer sees a different rainbow, created by the rays of light coming from behind him and from the raindrops in front of him.
What are rainbows made of?
The recipe for these optical phenomena in nature is simple: water droplets in the air, light and an observer. But it is not enough for the sun to appear when it rains. It should be low, and the observer should stand so that the sun is behind him, and look at the place where it is raining or has just rained.
A sunbeam coming from distant space catches a raindrop. Acting like a prism, a raindrop refracts every color hidden in the white light. Thus, when a white ray passes through a raindrop, it suddenly splits into beautiful multi-colored rays. Inside the drop, they encounter its inner wall, which acts like a mirror, and the rays are reflected in the same direction from which they entered the drop.
The end result is that the eyes see a rainbow of colors arching across the sky - light bent and reflected by millions of tiny raindrops. They can act like small prisms, splitting white light into a spectrum of colors. But rain is not always necessary to see a rainbow. Light can also be refracted by fog or sea vapors.
What color is the water?
The answer is obvious - the water is blue. If you pour clean water into a glass, everyone will see its transparency. This is because there is too little water in the glass and the color is too pale to see.
When filling a large glass container, you can see the natural blue tint of the water. Its color depends on how the water molecules absorb or reflect light. White light is made up of a rainbow of colors, and water molecules absorb most of the colors of the red to green spectrum that pass through them. And the blue part is reflected back. So we see blue.
Sunrises and sunsets
These are also examples of optical phenomena that humans observe every day. When the sun rises and sets, it directs its rays at an angle to the place where the observer is located. They have a longer path than when the sun is at its zenith.
Layers of air above the Earth's surface often contain a lot of dust or microscopic moisture particles. The sun's rays pass at an angle to the surface and are filtered. Red rays have the longest wavelength of radiation and therefore penetrate more easily to the ground than blue rays, which have short waves that are reflected by particles of dust and water. Therefore, during the morning and evening dawn, a person observes only part of the sun's rays that reach the earth, namely red ones.
Planet light show
A typical aurora is a colorful display of light in the night sky that can be seen every night at the North Pole. Changing in bizarre shapes, huge bands of blue-green light with orange and red spots sometimes reach more than 160 km in width and can extend 1,600 km in length.
How to explain this optical phenomenon, which is such a breathtaking spectacle? Auroras appear on Earth, but they are caused by processes occurring on the distant Sun.
How is everything going?
The Sun is a huge ball of gas consisting mainly of hydrogen and helium atoms. They all have protons with a positive charge and electrons with a negative charge orbiting around them. A halo of hot gas constantly spreads into space in the form solar wind. This countless number of protons and electrons rushes at a speed of 1000 km per second.
When solar wind particles reach Earth, they are attracted by a strong magnetic field planets. The Earth is a giant magnet with magnetic lines that converge at the North and South Poles. The attracted particles flow along these invisible lines near the poles and collide with the nitrogen and oxygen atoms that make up the Earth's atmosphere.
Some of the earth's atoms lose their electrons, others are charged with new energy. After colliding with protons and electrons from the Sun, they release photons of light. For example, nitrogen that has lost electrons attracts violet and blue light, while charged nitrogen glows dark red. Charged oxygen gives off green and red light. Thus, charged particles cause the air to shimmer in many colors. This is the aurora.
Mirages
It should be immediately determined that mirages are not a figment of human imagination, they can even be photographed, they are almost mystical examples of optical physical phenomena.
There is a lot of evidence of the observation of mirages, but science can provide a scientific explanation for this miracle. They can be as simple as a patch of water among the hot sands, or they can be stunningly complex, constructing visions of pillared hanging castles or frigates. All of these examples of optical phenomena are created by the play of light and air.
Light waves bend when they pass through first warm and then cold air. Hot air more rarefied than cold, so its molecules are more active and disperse over longer distances. As the temperature decreases, the movement of molecules also decreases.
Visions seen through the lenses of the earth's atmosphere may be greatly altered, compressed, expanded, or inverted. This is because light rays bend as they pass through warm and then cold air, and vice versa. And those images that the light stream carries with it, for example the sky, can be reflected on the hot sand and seem like a piece of water, which always moves away when approaching.
Most often, mirages can be observed at long distances: in deserts, seas and oceans, where hot and cold layers of air with different densities. It is the passage through different temperature layers that can twist the light wave and ultimately result in a vision that is a reflection of something and is presented by fantasy as a real phenomenon.
Halo
For most optical illusions that can be observed with the naked eye, the explanation is the refraction of sunlight in the atmosphere. One of the most unusual examples of optical phenomena is the solar halo. Essentially, a halo is a rainbow around the sun. However, it differs from an ordinary rainbow both in appearance and in its properties.
This phenomenon has many varieties, each of which is beautiful in its own way. But for any type of optical illusion to occur, certain conditions are necessary.
A halo appears in the sky when several factors coincide. Most often it can be seen in frosty weather when high humidity. There are a large number of ice crystals in the air. Making its way through them, sunlight is refracted in such a way that it forms an arc around the Sun.
And although the last 3 examples of optical phenomena are easily explained modern science, for the ordinary observer they often remain mystical and enigmatic.
Having examined the main examples of optical phenomena, we can confidently believe that many of them can be explained by modern science, despite their mysticism and mystery. But scientists still have a lot of discoveries ahead, clues to the mysterious phenomena that occur on planet Earth and beyond.
The atmosphere of our planet is a rather interesting optical system, the refractive index of which decreases with altitude due to a decrease in air density. Thus, earth's atmosphere can be considered as a “lens” of gigantic size, repeating the shape of the Earth and having a monotonically changing refractive index.
This circumstance leads to the emergence of a whole a number of optical phenomena in the atmosphere, caused by refraction (refraction) and reflection (reflection) of rays in it.
Let us consider some of the most significant optical phenomena in the atmosphere.
Atmospheric refraction
Atmospheric refraction- phenomenon curvature light rays as light passes through the atmosphere.
With height, the density of air (and therefore the refractive index) decreases. Let us imagine that the atmosphere consists of optically homogeneous horizontal layers, the refractive index of which varies from layer to layer (Fig. 299).
Rice. 299. Change in the refractive index in the Earth's atmosphere
When a light beam propagates in such a system, in accordance with the law of refraction, it will be “pressed” perpendicular to the layer boundary. But the density of the atmosphere does not decrease abruptly, but continuously, which leads to a smooth curvature and rotation of the beam by an angle α as it passes through the atmosphere.
As a result of atmospheric refraction, we see the Moon, Sun and other stars slightly higher than where they actually are.
For the same reason, the length of the day increases (in our latitudes by 10-12 minutes), and the disks of the Moon and Sun at the horizon shrink. Interestingly, the maximum angle of refraction is 35" (for objects near the horizon), which exceeds the visible angular size Sun (32").
From this fact it follows: at the moment when we see that the lower edge of the star has touched the horizon, in fact the solar disk is already below the horizon (Fig. 300).
Rice. 300. Atmospheric refraction of rays at sunset
Twinkling stars
Twinkling stars also related to astronomical refraction of light. It has long been noted that flickering is most noticeable in stars located near the horizon. Air currents in the atmosphere change the density of the air over time, which leads to the apparent flickering of the heavenly body. Astronauts in orbit do not observe any flickering.
Mirages
In hot desert or steppe regions and in polar regions, strong heating or cooling of air near the earth's surface leads to the appearance mirages: Thanks to the curvature of the rays, objects that are actually located far beyond the horizon become visible and appear close.
Sometimes similar phenomenon called terrestrial refraction. The occurrence of mirages is explained by the dependence of the refractive index of air on temperature. There are inferior and superior mirages.
Inferior Mirages can be seen on a hot summer day on a well-heated asphalt road: it seems to us that there are puddles ahead, which in fact are not there. In this case, we take for “puddles” the specular reflection of rays from non-uniformly heated layers of air located in close proximity to the “hot” asphalt.
Upper mirages They are distinguished by significant diversity: in some cases they give a direct image (Fig. 301, a), in others - an inverted image (Fig. 301, b), they can be double and even triple. These features are associated with different dependences of air temperature and refractive index on height.
Rice. 301. Formation of mirages: a - direct mirage; b - reverse mirage
Rainbow
Atmospheric precipitation leads to the appearance of spectacular optical phenomena in the atmosphere. Thus, during the rain, an amazing and unforgettable sight is the formation rainbows, which is explained by the phenomenon of different refraction (dispersion) and reflection of solar rays on the smallest droplets in the atmosphere (Fig. 302).
Rice. 302. Formation of a Rainbow
In particularly successful cases, we can see several rainbows at once, the order of the colors in which is reversed.
The light ray involved in the formation of a rainbow undergoes two refractions and multiple reflections in each raindrop. In this case, somewhat simplifying the mechanism of rainbow formation, we can say that spherical raindrops play the role of a prism in Newton’s experiment on the decomposition of light into a spectrum.
Due to spatial symmetry, the rainbow is visible in the form of a semicircle with an opening angle of about 42°, while the observer (Fig. 303) should be between the Sun and raindrops, with his back to the Sun.
The variety of colors in the atmosphere is explained by patterns light scattering on particles of various sizes. Due to the fact that blue color is scattered more strongly than red, during the day, when the Sun is high above the horizon, we see the sky blue. For the same reason, near the horizon (at sunset or sunrise), the Sun becomes red and not as bright as at the zenith. The appearance of colored clouds is also associated with the scattering of light by particles of various sizes in the cloud.
Literature
Zhilko, V.V. Physics: textbook. allowance for 11th grade. general education institutions with Russian language training with a 12-year period of study (basic and advanced) / V.V. Zhilko, L.G. Markovich. - Minsk: Nar. Asveta, 2008. - pp. 334-337.
