The 6th grade is studying the topic “Optical phenomena in the atmosphere” at school. However, it is of interest not only to the inquisitive mind of a child. Optical phenomena in the atmosphere, on the one hand, combine the rainbow, the change in the color of the sky during sunrises and sunsets, seen more than once by everyone. On the other hand, they include mysterious mirages, false Moons and Suns, impressive halos that in the past terrified people. The mechanism of formation of some of them remains unclear to the end today, however, the general principle by which optical phenomena "live" in nature has been well studied by modern physics.
Air shell
The Earth's atmosphere is a shell consisting of a mixture of gases and extending for about 100 km above sea level. The density of the air layer changes with distance from the earth: its highest value is at the surface of the planet, with height it decreases. The atmosphere cannot be called a static formation. Layers of the gaseous envelopeconstantly moving and mixing. Their characteristics change: temperature, density, speed of movement, transparency. All these nuances affect the sun's rays rushing to the surface of the planet.
Optical system
The processes occurring in the atmosphere, as well as its composition, contribute to the absorption, refraction and reflection of light rays. Some of them reach the target - the earth's surface, the other is scattered or redirected back into outer space. As a result of the curvature and reflection of light, the decay of part of the rays into a spectrum, and so on, various optical phenomena are formed in the atmosphere.
Atmospheric optics
At the time when science was in its infancy, people explained optical phenomena based on the prevailing ideas about the structure of the Universe. The rainbow connected the human world with the divine, the appearance of two false Suns in the sky testified to the approaching catastrophes. Today, most of the phenomena that frightened our distant ancestors have received a scientific explanation. Atmospheric optics is engaged in the study of such phenomena. This science describes optical phenomena in the atmosphere based on the laws of physics. She is able to explain why the sky is blue during the day, but changes color during sunset and dawn, how a rainbow is formed and where mirages come from. Numerous studies and experiments today make it possible to understand such optical phenomena in nature as the appearance of luminous crosses, Fata Morgana, rainbow halos.
Blue sky
Color of the skyso familiar that we rarely think about why it is so. Nevertheless, physicists know the answer well. Newton proved that under certain conditions a beam of light can be decomposed into a spectrum. When passing through the atmosphere, the part corresponding to the blue color is scattered better. The red section of visible radiation is characterized by a longer wavelength and is 16 times inferior to the violet in terms of the degree of scattering.
At the same time, we see the sky not purple, but blue. The reason for this lies in the peculiarities of the structure of the retina and the ratio of parts of the spectrum in sunlight. Our eyes are more sensitive to blue, and the violet portion of the sun's spectrum is less intense than blue.
Scarlet sunset
When people figured out what the atmosphere is, optical phenomena ceased to be for them evidence or an omen of terrible events. However, the scientific approach does not interfere with aesthetic pleasure from colorful sunsets and gentle sunrises. Bright reds and oranges, along with pinks and blues, gradually give way to night darkness or morning light. It is impossible to observe two identical sunrises or sunsets. And the reason for this lies in the same mobility of atmospheric layers and changing weather conditions.
During sunsets and sunrises, the sun's rays travel a longer path to the surface than during the day. As a result, diffused violet, blue and green go to the sides, and direct light turns red and orange. Clouds, dust or particles of ice contribute to the picture of sunset and dawn,suspended in the air. The light is refracted as it passes through them, and colors the sky in a variety of shades. On the part of the horizon opposite from the Sun, one can often observe the so-called Belt of Venus - a pink band separating the dark night sky and the blue day sky. The beautiful optical phenomenon, named after the Roman goddess of love, is visible before dawn and after sunset.
Rainbow Bridge
Perhaps, no other light phenomena in the atmosphere evoke so many mythological plots and fairy-tale images as those associated with the rainbow. The arc or circle, consisting of seven colors, is known to everyone since childhood. A beautiful atmospheric phenomenon that occurs during rain, when the sun's rays pass through the drops, fascinates even those who have thoroughly studied its nature.
And the physics of the rainbow today is no secret to anyone. Sunlight, refracted by drops of rain or fog, splits. As a result, the observer sees seven colors of the spectrum, from red to violet. It is impossible to define the boundaries between them. Colors blend smoothly into each other through several shades.
When observing a rainbow, the sun is always behind the person. The center of Irida's smile (as the ancient Greeks called the rainbow) is located on a line passing through the observer and the daylight. A rainbow usually appears as a semicircle. Its size and shape depend on the position of the Sun and the point at which the observer is located. The higher the luminary above the horizon, the lower the circle of possible appearance falls.rainbows. When the Sun passes 42º above the horizon, an observer on the Earth's surface cannot see the rainbow. The higher above sea level a person who wants to admire the smile of Irida is, the more likely that he will see not an arc, but a circle.
Double, narrow and wide rainbow
Often, along with the main one, you can see the so-called secondary rainbow. If the first is formed as a result of a single reflection of light, then the second is the result of a double reflection. In addition, the main rainbow is distinguished by a certain order of colors: red is located on the outside, and purple is on the inside, which is closer to the surface of the Earth. The side "bridge" is the spectrum reversed in sequence: violet is at the top. This happens because the rays from a raindrop are reflected from a double reflection at different angles.
Rainbows vary in color intensity and width. The brightest and rather narrow ones appear after a summer thunderstorm. Large drops, characteristic of such rain, give rise to a highly visible rainbow with distinct colors. Small droplets give a more blurry and less noticeable rainbow.
Optical phenomena in the atmosphere: aurora borealis
One of the most beautiful atmospheric optical phenomena is the aurora. It is characteristic of all planets with a magnetosphere. On Earth, auroras are observed at high latitudes in both hemispheres, in zones surroundingplanet's magnetic poles. Most often, you can see a greenish or blue-green glow, sometimes supplemented by flashes of red and pink along the edges. The intense aurora borealis is shaped like ribbons or folds of fabric, turning into spots as it fades. Stripes several hundred kilometers high stand out well along the lower edge against the dark sky. The upper limit of the aurora is lost in the sky.
These beautiful optical phenomena in the atmosphere still keep their secrets from people: the mechanism of the occurrence of certain types of luminescence, the cause of crackling during sharp flashes, has not been fully studied. However, the general picture of the formation of auroras is known today. The skies above the north and south poles are adorned with a greenish-pink glow as charged particles from the solar wind collide with atoms in Earth's upper atmosphere. The latter, as a result of the interaction, receive additional energy and emit it in the form of light.
Halo
The sun and moon often appear before us surrounded by a glow resembling a halo. This halo is a highly visible ring around the light source. In the atmosphere, most often it is formed due to the smallest particles of ice that make up cirrus clouds high above the Earth. Depending on the shape and size of the crystals, the characteristics of the phenomenon change. Often the halo takes the form of a rainbow circle as a result of the decomposition of the light beam into a spectrum.
An interesting variety of the phenomenon is called parhelion. As a result of the refraction of light in ice crystals onAt the level of the Sun, two bright spots are formed, resembling a daylight. In historical chronicles one can find descriptions of this phenomenon. In the past, it was often considered a harbinger of terrible events.
Mirage
Mirages are also optical phenomena in the atmosphere. They arise as a result of the refraction of light at the boundary between layers of air that differ significantly in density. The literature describes many cases when a traveler in the desert saw oases or even cities and castles that could not be nearby. Most often these are "lower" mirages. They arise over a flat surface (desert, asph alt) and represent a reflected image of the sky, which seems to the observer to be a body of water.
The so-called superior mirages are less common. They form over cold surfaces. Superior mirages are straight and inverted, sometimes they combine both positions. The most famous representative of these optical phenomena is Fata Morgana. This is a complex mirage that combines several types of reflections at once. Real-life objects appear before the observer, repeatedly reflected and mixed.
Atmospheric electricity
Electrical and optical phenomena in the atmosphere are often mentioned together, although the causes of their occurrence are different. The polarization of clouds and the formation of lightning are associated with processes occurring in the troposphere and ionosphere. Giant spark discharges are usually formed during a thunderstorm. Lightning occurs inside clouds and can strike the ground. They are life threateningpeople, and this is one of the reasons for the scientific interest in such phenomena. Some properties of lightning are still a mystery to researchers. Today, the cause of ball lightning is unknown. As with some aspects of aurora and mirage theory, electrical phenomena continue to intrigue scientists.
Optical phenomena in the atmosphere, briefly described in the article, are becoming more and more understandable for physicists every day. At the same time, they, like lightning, never cease to amaze people with their beauty, mystery and sometimes grandiosity.
