At school he studies the topic " Optical phenomena in the atmosphere" grade 6. However, it is of interest not only to an inquiring children's mind. Optical phenomena in the atmosphere, on the one hand, combine a rainbow, a change in the color of the sky during sunrises and sunsets, more than once seen by everyone. On the other hand, they include mysterious mirages, false moons and suns, impressive halo, which in the past terrified people. The mechanism of formation of some of them is still incomprehensible today, however, modern physics has well studied the general principle by which optical phenomena in nature “live” in nature.
Air shell
The atmosphere of the Earth is a shell consisting of a mixture of gases and extending about 100 km above sea level. The density of the air layer changes with distance from the earth: its greatest value is at the surface of the planet, it decreases with height. The atmosphere cannot be called a static formation. The layers of the gas shell are constantly moving, mixing. Their characteristics are changing: temperature, density, speed, transparency. All these nuances affect the sun's rays rushing to the surface of the planet.
Optical system
The processes taking place in the atmosphere, as well as its composition contribute to the absorption, refraction and reflection of light rays. Some of them reach the goal - the earth's surface, another 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 a time when science was only in its infancy, people explained optical phenomena based on prevailing ideas about the structure of the Universe. A 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 received a scientific explanation. The study of such phenomena deals with atmospheric optics. This science describes optical phenomena in the atmosphere based on the laws of physics. She is able to explain why the sky is blue during the day, and during sunset and dawn changes color, how a rainbow forms and where mirages come from. Numerous studies and experiments today make it possible to understand such optical phenomena in nature as the appearance of luminous crosses, Fata Morgana, and rainbow halo.
Blue sky
The color of the sky is so familiar that we rarely wonder why it is so. Nevertheless, the answer is well known to physicists. Newton proved that under certain conditions a ray of light is decomposed into a spectrum. With the passage of the atmosphere, its part corresponding to blue color dissipates better. The red portion of visible radiation is characterized by a longer wavelength and is 16 times inferior to the violet in scattering.
Moreover, the sky we see is not purple, but blue. The reason for this lies in the features of the device of the retina and the ratio of the parts of the spectrum in sunlight. Our eyes are more sensitive to blue, and the violet portion in the spectrum of the star is less intense than blue.
Scarlet sunset
When people understood what the atmosphere was, optical phenomena ceased to be evidence or an omen of terrible events for them. However, the scientific approach does not prevent aesthetic pleasure from colorful sunsets and gentle sunrises. Vibrant reds and oranges along with pink and blue 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 the atmospheric layers and the change in weather conditions.
During sunsets and sunrises, the sun's rays travel a longer path to the surface than during the day. As a result, scattered violet, blue and green go to the sides, and direct light turns red and orange. Clouds, dust, or particles of ice suspended in the air contribute to the picture of sunset and dawn. The light is refracted through them, and colors the sky in a variety of shades. On the horizon section opposite the Sun, one can often see the so-called Belt of Venus - a pink strip separating the dark night sky and the blue daylight. A beautiful optical phenomenon, named after the Roman goddess of love, is visible before sunrise and after sunset.
Rainbow bridge
Perhaps, no other light phenomena in the atmosphere evoke as many mythological plots and fairy-tale images as are associated with a 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 droplets, fascinates even those who have thoroughly studied its nature.
And rainbow physics is no secret to anyone today. Sunlight, refracted by raindrops or fog, splits. As a result, the observer sees seven colors of the spectrum, from red to purple. The boundaries between them cannot be determined. Colors smoothly transition into each other through several shades.
When observing a rainbow, the sun is always located behind a person’s back. The center of the smile of Irida (the ancient Greeks called the rainbow) is located on the line passing through the observer and the daylight. Usually a rainbow appears in the form of a semicircle. Its size and shape depend on the position of the Sun and the point at which the observer is located. The higher the luminary above the horizon, the lower the circle of the possible appearance of the rainbow. When the Sun overcomes the 42º mark above the horizon, an observer on the surface of the Earth cannot see the rainbow. The higher the man is located above the sea level who wants to admire the smile of Irida, the more likely he is to see not an arc, but a circle.
Double, narrow and wide rainbow
Often, along with the main one, you can see the so-called side rainbow. If the first is formed as a result of a single reflection of light, then the second is the result of a double. 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 Earth's surface. The secondary “bridge” is a spectrum that is inverse in sequence: purple appears at the top. This happens because when double reflected from a raindrop, the rays come out from different angles.
Rainbows vary in color intensity and width. The brightest and rather narrow appear after a summer thunderstorm. Large drops characteristic of such rain give rise to a clearly visible rainbow with distinctly visible colors. Small droplets give a more vague and less noticeable rainbow.
Optical phenomena in the atmosphere: aurora
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 of both hemispheres, in the zones surrounding the planet’s magnetic poles. Most often you can see a greenish or blue-green glow, sometimes supplemented at the edges with flashes of red and pink. Intense aurora in shape resembles ribbons or folds of fabric that, when damped, turn into spots. Stripes several hundred kilometers high stand out along the lower edge against a dark sky. The upper limit of the aurora is lost at a height.
These beautiful optical phenomena in the atmosphere still keep their secrets from people: the mechanism of the appearance of certain types of luminescence, the cause of cod during sudden flashes, has not been fully studied. However, the general picture of the formation of auroras is known today. The sky above the north and south poles is decorated with a greenish-pink glow when charged particles of the solar wind collide with the atoms of the upper layers of the earth's 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 clearly visible ring around the light source. In the atmosphere, it is most often formed due to the smallest particles of ice making 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 a light beam into a spectrum.
An interesting variation of the phenomenon is called pargelium. As a result of the refraction of light in ice crystals at the level of the Sun, two bright spots are formed, resembling a daylight. In historical chronicles you can find descriptions of this phenomenon. In the past, it was often considered a harbinger of terrible events.
Mirage
Mirages are also optical phenomena in the atmosphere. They arise as a result of the refraction of light at the boundary between layers of air significantly differing in density. The literature describes many cases when a traveler in the desert saw oases or even cities and castles, which could not be nearby. Most often these are “lower” mirages. They arise over a flat surface (desert, asphalt) and are a reflected image of the sky, which seems to the observer to a body of water.
The so-called upper mirages are less common. They form over a cold surface. Upper mirages are straight and inverted, sometimes 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. The observer is presented with real objects, repeatedly reflected and mixed.
Atmospheric electricity
Electrical and optical phenomena in the atmosphere are often referred to together, although the causes of their occurrence are different. Cloud polarization and the formation of lightning are associated with processes occurring in the troposphere and ionosphere. Giant spark discharges usually form during thunderstorms. Lightning occurs inside the clouds, can strike the ground. They are a threat to people's lives, 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 the occurrence of ball lightning is unknown. As is the case with some aspects of the theory of auroras and mirages, electrical phenomena continue to intrigue scientists.
Optical phenomena in the atmosphere, briefly described in the article, are becoming more and more understandable to physicists every day. At the same time, they, like lightning, do not cease to delight people with their beauty, mystery and sometimes grandeur.