Since ancient times, mirages, flickering figures in the air have alarmed and terrified people. Today, scientists have revealed many secrets of nature, including optical phenomena. They are not surprised by natural puzzles, the essence of which has long been studied. In high school today, optical phenomena in physics in the 8th grade are held, so any student can understand their nature.
Basic concepts
Ancient scholars believed that the human eye sees through the palpation of objects with the finest tentacles. Optics at that time was a doctrine 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 questions concerning vision are studied by physiological optics.
Optical phenomena, on the other hand, are manifestations of diverse actions performed by light rays. They are studied by atmospheric optics.
Unusual processes in the atmosphere
The planet Earth is surrounded by a gas shell, called the atmosphere. Its thickness is hundreds of kilometers. Closer to Earth, the atmosphere is more dense, upward rarefied. The physical properties of the atmospheric envelope are constantly changing, the layers are mixed. Change the temperature indicators. Density, degree of transparency are shifted.
Light rays come from the Sun and other celestial bodies towards the Earth. They pass through the Earth’s atmosphere, which for them serves as a specific optical system that changes its characteristics. Light rays are reflected, scattered, pass through the atmosphere, illuminate the earth. Under certain conditions, the path of the rays bends, so a variety of phenomena arise. The most original optical phenomena of physics are:
- sunset of the sun;
- the appearance of a rainbow;
- Northern Lights;
- mirage;
- halo.
Let's consider them in more detail.
Halo around the sun
The word "halo" in Greek means "circle". What optical phenomenon underlies it?
A halo is a process of light 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. Typically, halo form in front of cyclones and may be their precursors.
Water droplets freeze in the air and take the correct prism shape with six sides. Everyone is familiar with icicles that appear in the lower atmospheric layers. Upstairs, such ice needles freely descend vertically. Crystal ice floes swirl, descend to the ground, while they are parallel to the ground. 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 undergo a number of other processes. It rarely happens that all processes are clearly visible, usually one or another part of the phenomenon is more pronounced, 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 refraction in needles from ice flying in the air. The rays in the prisms deviate at an angle of 22 degrees, so those that pass through the crystals are shown to the observer as deviated by 22 degrees. Therefore, the inner space seems dark.
Red color is refracted less, it is shown the least deviated from the sun. Followed by yellow. Other rays mix and appear white.
There is a halo with an angle of 46 degrees, it is located around the halo of 22 degrees. Its inner region is also reddish, because the light undergoes refraction in ice needles, turned 90 degrees to the sun.
A 90-degree halo is also known, it glows weakly, has almost no color or is painted red on the outside. Scientists have not yet fully studied this variety.
Halo around the moon and other species
This optical phenomenon is often seen when there are light clouds and many tiny 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, going into the opposite part, is refracted by 22 degrees.
In winter, a halo can be seen in the cold air near streetlights. It appears due to the light of a lantern.
Around the sun, a halo can also form in the 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.
A halo may look like a circle of rainbow color around the sun. It appears if in the atmosphere there are many crystals with six faces, but they do not reflect, but refract the rays of the sun. At the same time, most of the rays are scattered, not reaching our eyes. The remaining rays reach the human eyes, and we notice a rainbow circle around the Sun. Its radius is approximately 22 degrees or 46 degrees.
False sun
Scientists noted that the halo circumference is always brighter on the sides. This is due to the fact that there are vertical and horizontal halo. False suns may appear at their intersections. This happens especially often when the Sun is not far from the horizon, at which time we no longer see part of the vertical circle.
The false sun is also an optical phenomenon, a kind of halo. It appears due to ice crystals with six faces, having a shape resembling nails. Such crystals soar in the atmosphere in a vertical direction, light is refracted in their lateral 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 piece of arc or a luminous spot of incomprehensible shape. Sometimes false suns are so bright that they cannot be distinguished 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 a bridge from heaven to earth. Aristotle believed that a rainbow appears due to the reflection of drops of sunlight. What optical phenomenon is still able to please a person as much as a rainbow does?
In the 17th century, Descartes studied the nature of the rainbow. Newton later conducted experiments with light and supplemented Descartes' theory, but could not understand the formation of several rainbows, the absence of separate color shades in them.
The complete rainbow theory was introduced 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 accepted today.
A rainbow appears when the light of the sun falls on a curtain of rainwater in the sky inverse from the Sun. The center of the rainbow is located at a point on the back of the sun, that is, it is not visible to the human eye. The rainbow arc is part of the circle around this central point.
The colors in the rainbow are arranged in a specific order. He is constant. Red is on the top, purple is on the bottom. Between them, the colors go in a strict arrangement. Not all colors exist in the rainbow. The predominance of green indicates a transition to favorable weather.
Polar Lights
This glow in the upper magnetic layers of the atmosphere due to the interaction of atoms and elements of the solar wind. Usually auroras have a green or blue hue with a touch of pink and red. They may be in the form of tape or spots. Their bursts often accompany noisy sounds.
Mirage
Simple mirage deceptions are familiar to any person. For example, when driving on heated asphalt, a mirage appears as a water surface. This is not surprising to anyone. What optical phenomenon explains the appearance of mirages? Let us dwell on this issue in more detail.
A mirage is an optical physical phenomenon in the atmosphere, as a result of which the eye sees objects hidden from view under ordinary conditions. This is due to the refraction of the light beam when flowing through the air layers. Objects located at a considerable distance, in this case, may rise or fall relative to their true location, and may be distorted and acquire bizarre outlines.
Broken Ghost
This is a phenomenon in which, at sunset or sunrise, the shadow of a person on a raised platform takes on an incomprehensible scale, as it falls on clouds nearby. This is due to the reflection and refraction of light rays by water droplets in foggy conditions. The phenomenon was named after one of the heights of the Germanic Harz Mountains.
Lights of St. Elmo
These are luminous brushes of blue or violet color on the masts of ships. Lights can appear on mountain hills, on buildings of impressive height. This phenomenon occurs due to electric discharges at the ends of the conductors due to the increase in electric tension.
These are the optical phenomena considered in class 8. Let's talk about optical devices.
Designs in optics
Optical devices are devices that convert light radiation. Typically, these devices operate in visible light.
All optical devices can be divided into two types:
- Devices in which the image is displayed 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 magnifier, a microscope, telescopes. These devices are considered visual.
A camera is an optical-mechanical device used to obtain images of an object on photographic film. The design of the camera includes a camera and lenses that make up the lens. The lens creates an inverted reduced image of the object, fixed on the 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 called a negative, in it bright places look dark, and vice versa. With a negative make positive on photosensitive paper. Using the enlarger, the image is enlarged.
A magnifier is a lens or lens system designed to magnify objects as they are viewed. The magnifier is placed next to the eye, select the distance from which the subject is seen clearly. The use of a magnifying glass is based on increasing the angle of view under which the subject is viewed.
To obtain a larger angular magnification, use a microscope. In this device, the increase in objects is 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 examined the main optical phenomena and devices, their varieties and features.