For a long time, mirages, flickering figures in the air, alarmed and terrified people. Nowadays, scientists have revealed many secrets of nature, including optical phenomena. They are not surprised by natural mysteries, the essence of which has long been studied. In high school today, optical phenomena are taught in physics in the 8th grade, so any student can understand their nature.
Basic concepts
Scientists of antiquity believed that the human eye sees by feeling objects with the thinnest tentacles. Optics at that time was the study of vision.
In the Middle Ages, optics studied light and its essence.
Today, optics is a part of physics that studies the propagation of light through various media and its interaction with other substances. All issues related to vision are studied by physiological optics.
Optical phenomena are manifestations of diverse actions performed by rays of light. They are studied by atmospheric optics.
Unusual processes in the atmosphere
Planet Earth is surrounded by a gaseous shell called the atmosphere. Its thickness is hundreds of kilometers. Closer to the Earth, the atmosphere is denser, in the directionupward is sparse. The physical properties of the atmospheric shell are constantly changing, the layers are mixed. Change temperatures. Density, transparency shift.
Light rays go from the Sun and other celestial bodies towards the Earth. They pass through the Earth's atmosphere, which serves as a specific optical system for them, changing its characteristics. Light rays reflect, scatter, pass through the atmosphere, illuminate the earth. Under certain conditions, the path of the rays is bent, so various phenomena occur. Physicists consider the most original optical phenomena:
- sunshine sunset;
- appearance of the rainbow;
- northern lights;
- mirage;
- halo.
Let's take a closer look at them.
Halo around the Sun
The very word "halo" in Greek means "circle". What optical phenomenon underlies it?
Halo is a process of refraction and reflection of rays that occurs in cloud crystals high in the atmosphere. The phenomenon looks like luminous rays near the Sun, limited by a dark interval. Halos usually form before cyclones and may be their precursors.
Water drops freeze in the air and take the correct prismatic shape with six sides. Everyone is familiar with icicles appearing in the lower atmospheric layers. At the top, such ice needles freely fall in the vertical direction. Crystalline ice floes are spinning, descending to the ground, while they have a parallel arrangement alongrelation to the earth. A person directs vision through crystals, which act as lenses and refract light.
Other prisms are flat or look like stars with six rays. Rays of light falling on crystals may not undergo refraction or experience a number of other processes. It rarely happens that all processes are clearly visible, usually one or another part of the phenomenon appears more clearly, while others are poorly represented.
A small halo is a circle around the sun with a radius of about 22 degrees. The color of the circle is reddish from the inside, then flows into yellow, white and mixes with the blue sky. The inner area of the circle is dark. It is formed as a result of light refraction in ice needles flying in the air. The rays in the prisms are deflected at an angle of 22 degrees, so those that have passed through the crystals appear to the observer deflected by 22 degrees. Therefore, the interior appears dark.
Red color is refracted less, showing the least deflected from the sun. Next up is yellow. The other rays mix and appear white.
There is a 46 degree halo around the 22 degree halo. Its inner region is also reddish because light is refracted in ice needles that are 90 degrees facing the sun.
The 90-degree halo is also known, it glows faintly, has almost no color or is colored red on the outside. Scientists have not yet fully studied this variety.
Halo around the Moonand other species
This optical phenomenon is often seen when there are light clouds and many miniature crystalline ice floes in the sky. Each such crystal is a kind of prism. Basically, their shape is elongated hexagons. Light enters the front crystalline region and, exiting the opposite part, is refracted by 22 degrees.
In the winter, a halo can be seen in the cold air near the street lamps. It appears from the light of a lantern.
A halo around the Sun can also form in frosty snowy air. Snowflakes are in the air, light passes through the clouds. In the evening sunset, this light turns red. In past centuries, superstitious people were horrified by such phenomena.
The halo may look like a rainbow colored circle around the Sun. It appears if there are many crystals with six faces in the atmosphere, but they do not reflect, but refract the rays of the sun. Most of the rays are scattered, not reaching our eyes. The rest of the rays reach the human eye, and we notice an iridescent circle around the Sun. Its radius is approximately 22 degrees or 46 degrees.
False Sun
Scientists have noted that the halo circle is always brighter on the sides. This is explained by the fact that vertical and horizontal halos meet here. False suns may appear at their intersections. This happens especially often when the Sun is close to the horizon, at which time we can no longer see part of the vertical circle.
The false sun is also an optical phenomenon, a kind of halo. It appears due toice crystals with six faces, shaped like nails. Such crystals hover in the atmosphere in a vertical direction, light is refracted in their side faces.
A third "sun" can also form if only the surface part of the halo circle is visible above the true sun. It can be a segment of an arc or a luminous spot of an incomprehensible shape. Sometimes false suns are so bright that they are indistinguishable from the real Sun.
Rainbow
This is an atmospheric optical phenomenon in the form of an incomplete circle with different colors.
Religions of antiquity considered the rainbow as a bridge from heaven to earth. Aristotle believed that the rainbow appears due to the reflection of drops of sunlight. What optical phenomenon can still please a person as much as a rainbow does?
In the 17th century, Descartes studied the nature of the rainbow. Later, Newton experimented with light and supplemented the theory of Descartes, but could not understand the formation of several rainbows, the absence of individual color shades in them.
The complete theory of the rainbow was presented in the 19th century by an astronomer from England, D. Erie. It was he who managed to reveal all the processes of the rainbow. The theory he developed is still accepted today.
A rainbow appears when the light of the sun hits a curtain of rainwater in the region of the sky opposite the Sun. The center of the rainbow is located at a point on the far side of the Sun, that is, it is not visible to the human eye. The arc of the rainbow is the part of the circle around this central point.
The colors in the rainbow are placed in a certain order. He is constant. Red is on the top edge, purple is on the bottom. Between them, the colors go in a strict arrangement. The rainbow does not contain all the existing colors. The predominance of green indicates the transition to favorable weather.
Aurora Borealis
This is a glow in the upper magnetic layers of the atmosphere due to the mutual influence of atoms and elements of the solar wind. Aurora are usually green or blue with hints of pink and red. They may be in the form of a ribbon or a spot. Their bursts are often accompanied by noisy sounds.
Mirage
Simple mirage deceptions are familiar to any person. For example, when driving on heated asph alt, a mirage appears as a water surface. This comes as no surprise to anyone. What optical phenomenon explains the appearance of mirages? Let's dwell on this issue in more detail.
Mirage is an optical physical phenomenon in the atmosphere, as a result of which the eye sees objects that are hidden from view under normal conditions. This is due to the refraction of the light beam as it flows through the air layers. Objects that are at a considerable distance may rise or fall relative to their true location, or may be distorted and take on bizarre shapes.
Brocken Ghost
This is a phenomenon in which, at sunset or sunrise, the shadow of a person who is on an elevation acquires incomprehensible proportions, as it falls on clouds nearby. This is explainedreflection and refraction of light rays by water droplets in foggy conditions. The phenomenon was named after one of the heights of the German Harz mountains.
St. Elmo's Fire
These are luminous brushes of blue or purple color on the masts of sea vessels. Lights can appear on mountainous heights, on buildings of impressive height. This phenomenon occurs due to electric discharges at the ends of the conductors due to the fact that the electrical tension increases.
These are the optical phenomena considered in the 8th grade lessons. Let's talk about optical devices.
Designs in optics
Optical devices are devices that convert light radiation. Usually these devices work in visible light.
All optical devices can be divided into two types:
- Devices in which the image is obtained on the screen. These are cameras, movie cameras, projection devices.
- Devices that interact with the human eye, but do not form images on the screen. This is a magnifying glass, microscope, telescopes. These devices are considered visual.
A camera is an opto-mechanical device used to obtain images of an object on film. The design of the camera includes a camera and lenses that form the lens. The lens creates an inverted miniature image of the object that is captured on film. This is due to the action of light.
The image is initially invisible, but thanks to the developing solution, it becomes visible. This image is callednegative, in it bright places look dark, and vice versa. Make a positive from the negative on photosensitive paper. Using a photo enlarger, the image is enlarged.
A magnifying glass is a lens or lens system designed to magnify objects while looking at them. The magnifying glass is placed next to the eye, the distance from which the object is seen clearly is selected. The use of a magnifying glass is based on increasing the angle of view from which the object is viewed.
To get more angular magnification, use a microscope. In this device, the magnification of objects occurs due to the optical system, consisting of a lens and an eyepiece. First, the angle of view is increased by the lens, then by the eyepiece.
So, we have considered the main optical phenomena and devices, their varieties and features.
