For example, why is the sky blue? Why is the sky blue? Why is the sky NOT purple?

Sunlight is white, that is, it includes all the colors of the spectrum. It would seem that the sky should also be white, but it is blue.

Surely your child knows the phrase “Every Hunter Wants to Know Where the Pheasant Sits,” which helps to remember the colors of the rainbow. And a rainbow is the best way to understand how light breaks up into waves of different frequencies. The longest wavelength is for red, the shortest for violet and blue.

Air, which contains gas molecules, ice microcrystals and water droplets, scatters short-wavelength light more strongly, so there are eight times more blue and violet colors in the sky than red. This effect is called Rayleigh scattering.

Draw an analogy with balls rolling down a corrugated board. The larger the ball, the less likely it is to veer off course or get stuck.

Explain why the sky cannot be any other color

Why isn't the sky purple?

It is logical to assume that the sky should be purple, because this color has the shortest wavelength. But here the peculiarities of sunlight and the structure of the human eye come into play. The spectrum of sunlight is uneven; there are fewer shades of violet than other colors. And part of the spectrum is not visible to the human eye, which further reduces the percentage of shades of violet in the sky.

Why isn't the sky green?

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A child may ask: “Since scattering increases with decreasing wavelength, why is the sky not green?” Not only blue rays are scattered in the atmosphere. Their wavelength is the shortest, so they are the most visible and brightest. But if the human eye were constructed differently, the sky would appear green to us. After all, the wavelength of this color is slightly longer than that of blue.

Light is structured differently than paint. If you mix green, blue and purple paints, you get a dark color. With light, the opposite is true: the more colors are mixed, the lighter the result.

Tell me about the sunset

We see blue sky when the Sun shines from above. When it approaches the horizon, and the angle of incidence of the sun's rays decreases, the rays travel tangentially, covering a much longer path. Because of this, blue-blue spectrum waves are absorbed in the atmosphere and do not reach the Earth. Red and yellow colors are scattered in the atmosphere. That's why the sky turns red at sunset.

Why is the sky blue? It is very difficult to find an answer to such a simple question. Many scientists racked their brains in search of an answer. The best solution to the problem was proposed about 100 years ago by the English physicist Lord John Rayleigh.

But let's start from the beginning. The sun emits dazzlingly pure white light. This means that the color of the sky should be the same, but it is still blue. What happens to white light in the earth's atmosphere?

A little about color

White light is a mixture of colored rays. Using a prism we can make a rainbow. The prism splits the white beam into colored stripes: red, orange, yellow, green, blue, indigo and violet. Combining together, these rays again form white light. It can be assumed that sunlight is first split into colored components. Then something happens, and only blue rays reach the surface of the Earth.

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So why is the sky blue?

There are several possible explanations. The air surrounding the Earth is a mixture of gases: nitrogen, oxygen, argon and others. There is also water vapor and ice crystals in the atmosphere. Dust and other small particles are suspended in the air. In the upper layers of the atmosphere there is a layer of ozone. Could this be the reason?

Some scientists believed that ozone and water molecules absorb red rays and transmit blue ones. But it turned out that there was simply not enough ozone and water in the atmosphere to color the sky blue.

In 1869, Englishman John Tyndall proposed that dust and other particles scatter light. Blue light is scattered the least and passes through layers of such particles to reach the Earth's surface. In his laboratory, he created a model of smog and illuminated it with a bright white beam. The smog turned a deep blue.

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Tindall decided that if the air were absolutely clear, then nothing would scatter the light, and we could admire the bright white sky. Lord Rayleigh also supported this idea, but not for long. In 1899, he published his explanation: it is air, not dust or smoke, that turns the sky blue.

The relationship between color and wavelength - an explanation of why the sky is blue

Some of the sun's rays pass between gas molecules without colliding with them and reach the Earth's surface unchanged. The other, larger part is absorbed by gas molecules. When photons are absorbed, molecules become excited, that is, they are charged with energy, and then emit it in the form of photons. These secondary photons have different wavelengths and can be any color from red to violet.

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They scatter in all directions: towards the Earth, and towards the Sun, and to the sides. Lord Rayleigh suggested that the color of the emitted beam depends on the predominance of quanta of one color or another in the beam. When a gas molecule collides with photons of solar rays, there are eight blue quanta per secondary red quantum.

What is the result? Intense blue light literally pours down on us from all directions from billions of gas molecules in the atmosphere. This light has photons of other colors mixed in, so it is not purely blue.

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The bottomless blue sky amazes with its splendor and purity. Whether the Creator created it this way or whether it appeared on its own during the process of formation is not so important.

The main thing is that on clear sunny days a person sees a beautiful blue expanse of sky above his head, which fills his heart and soul with the light of life. Many poetic lines have been written about the blueness of the firmament; the blue-blue sky is captured in thousands of amateur and professional photographs; the sky inspires artists to create truly magical landscapes and, finally, the transparent blue sky can be called a symbol of Eternity and Love.

While admiring the beauty of the sky, many of us do not think about why the sky is blue during daylight hours. But one day, having decided to find the answer to this question, a person may encounter obscure explanations.

If you are by nature more of a lyricist than a physicist, then what is written in this article will seem clear and accessible to you. And simply knowing the reason why the sky is blue will not deprive you of a reverent attitude towards the infinitely blue, like a huge sea.

Most often, the sky is the dome-shaped space above the earth, which consists of a mixture of nitrogen, oxygen, carbon dioxide and water vapor. The blue color of the sky comes from the sun's rays penetrating the atmosphere. What happens in the sky with the rays of the sun, which are multicolored by nature? When sunlight hits air molecules, it scatters onto them. And the smaller components of the air mass - electrons - emit this light.


According to Rayleigh's law, light with shorter wavelengths scatters faster. And the blue, indigo and violet color spectrum, into which a solar ray decomposes during interaction with gases, has a significantly shorter wavelength than red, yellow, orange and green. As a result, it turns out that blue-blue directly depends on the speed of dispersion of waves corresponding in color.

The same principle explains the red color of the sky at sunset. As night approaches, the Earth's atmospheric layer increases, and short rays of the blue, blue and violet spectrum are scattered in the upper layers. And in that part of the atmosphere that a person sees, the rays of the red spectrum predominate.

Whatever the sky above our heads, it is inseparably connected with all the processes occurring in the Earth’s atmosphere. Whether it rains or snows, the sky will certainly turn gray. In inclement weather the sky is said to frown or cry. This means that in people’s imaginations the sky is captured in blue-blue tones.

The dream of a blue sky on rainy days never leaves a person. Even those who love the melancholy mood evoked by rain look forward to the sunbeam appearing from behind the clouds and the sky shining with its alluring blue.

In summer there is nothing more beautiful than lying in the soft fragrant grass and looking at the sky. To drown your eyes in it and not think about why it is so blue. Watch the measured flight of birds and not remember that the sky can be truly angry.


Trying to see angels in the sky and not feel the hot rays of the sun on your skin. You can experiment with the sky, show your imagination, just live. And, following the famous lines of the Russian poet Boris Pasternak

“In everything I want to get to the very essence
In work, in search of a path, in heartfelt turmoil..."

to get to the essence of the sky, which is certainly contained in its wonderful blueness.

To do this, you don’t need to become an artist, poet, musician - you can learn to feel the sky not only above your head, but also inside yourself, being a teacher, a taxi driver, and a businessman. By sorting life along the color spectrum, like a sunbeam, you need to quickly become a participant in various events and at the same time scatter exceptionally pure, kind light, reminding people of the blue sky.

On a clear sunny day, the sky above us looks bright blue. In the evening, the sunset colors the sky in red, pink and orange. Why is the sky blue? What makes a sunset red?

To answer these questions, you need to know what light is and what the Earth's atmosphere is made of.

Atmosphere

The atmosphere is a mixture of gases and other particles that surround the earth. The atmosphere mainly consists of nitrogen (78%) and oxygen (21%) gases. Argon gas and water (in the form of steam, droplets and ice crystals) are the next most common in the atmosphere, their concentration does not exceed 0.93% and 0.001%, respectively. The Earth's atmosphere also contains small quantities of other gases, as well as tiny particles of dust, soot, ash, pollen and salt that enter the atmosphere from the oceans.

The composition of the atmosphere varies within small limits depending on location, weather, etc. The concentration of water in the atmosphere increases during storms, as well as near the ocean. Volcanoes are capable of throwing huge amounts of ash high into the atmosphere. Man-made pollution can also add various gases or dust and soot to the normal composition of the atmosphere.

The density of the atmosphere at low altitudes near the Earth's surface is greatest; with increasing altitude it gradually decreases. There is no clearly defined boundary between the atmosphere and space.

Light waves

Light is a type of energy that is transported by waves. In addition to light, waves carry other types of energy, for example, a sound wave is a vibration of air. A light wave is an oscillation of electric and magnetic fields, this range is called the electromagnetic spectrum.

Electromagnetic waves travel through airless space at a speed of 299.792 km/s. The speed at which these waves propagate is called the speed of light.

Radiation energy depends on the wavelength and its frequency. Wavelength is the distance between the two closest peaks (or troughs) of the wave. The frequency of a wave is the number of times a wave oscillates per second. The longer the wave, the lower its frequency, and the less energy it carries.

Visible light colors

Visible light is the part of the electromagnetic spectrum that can be seen by our eyes. The light emitted by the Sun or an incandescent lamp may appear white, but it is actually a mixture of different colors. You can see the different colors of the visible spectrum of light by breaking it down into its components using a prism. This spectrum can also be observed in the sky in the form of a rainbow, resulting from the refraction of light from the Sun in water droplets, acting as one giant prism.

The colors of the spectrum mix and continuously transform into one another. At one end the spectrum has red or orange colors. These colors smoothly transition into yellow, green, blue, indigo and violet. Colors have different wavelengths, different frequencies, and differ in energies.

Propagation of light in air

Light travels through space in a straight line as long as there are no obstacles in its path. When a light wave enters the atmosphere, the light continues to travel in a straight line until dust or gas molecules get in its way. In this case, what happens to the light will depend on its wavelength and the size of the particles caught in its path.

Dust particles and water droplets are much larger than the wavelength of visible light. Light is reflected in different directions when it hits these large particles. Different colors of visible light are reflected equally by these particles. Reflected light appears white because it still contains the same colors that were present before it was reflected.

Gas molecules are smaller than the wavelength of visible light. If a light wave collides with them, the result of the collision may be different. When light collides with a molecule of any gas, some of it is absorbed. A little later, the molecule begins to emit light in different directions. The color of the light emitted is the same color that was absorbed. But colors of different wavelengths are absorbed differently. All colors can be absorbed, but higher frequencies (blue) are absorbed much more strongly than lower frequencies (red). This process is called Rayleigh scattering, named after the British physicist John Rayleigh, who discovered this scattering phenomenon in the 1870s.

Why is the sky blue?

The sky is blue due to Rayleigh scattering. As light travels through the atmosphere, most of the long wavelengths of the optical spectrum pass through unchanged. Only a small portion of red, orange and yellow colors interact with air.

However, many shorter wavelengths of light are absorbed by gas molecules. Once absorbed, the blue color is emitted in all directions. It is scattered everywhere in the sky. No matter which direction you look, some of this scattered blue light reaches the observer. Since blue light is visible everywhere overhead, the sky appears blue.

If you look towards the horizon, the sky will have a paler hue. This is the result of light traveling a greater distance through the atmosphere to reach the observer. The scattered light is scattered again by the atmosphere and less blue light reaches the observer's eyes. Therefore, the color of the sky near the horizon appears paler or even appears completely white.

Black sky and white sun

From Earth, the Sun appears yellow. If we were in space or on the Moon, the Sun would appear white to us. There is no atmosphere in space to scatter sunlight. On Earth, some of the short wavelengths of sunlight (blue and violet) are absorbed by scattering. The rest of the spectrum appears yellow.

Also, in space, the sky appears dark or black instead of blue. This is the result of the absence of an atmosphere, therefore the light is not scattered in any way.

Why is the sunset red?

When the Sun goes down, sunlight has to travel a greater distance in the atmosphere to reach the observer, so more sunlight is reflected and scattered by the atmosphere. Since less direct light reaches the observer, the Sun appears less bright. The color of the Sun also appears different, ranging from orange to red. This happens because even more short-wavelength colors, blue and green, are scattered. Only the long-wave components of the optical spectrum remain, which reach the observer’s eyes.

The sky around the setting sun can have different colors. The sky is most beautiful when the air contains many small particles of dust or water. These particles reflect light in all directions. In this case, shorter light waves are scattered. The observer sees light rays of longer wavelengths, which is why the sky appears red, pink or orange.

More about the atmosphere

What is atmosphere?

The atmosphere is a mixture of gases and other substances that surround the Earth in the form of a thin, mostly transparent shell. The atmosphere is held in place by the Earth's gravity. The main components of the atmosphere are nitrogen (78.09%), oxygen (20.95%), argon (0.93%) and carbon dioxide (0.03%). The atmosphere also contains small amounts of water (in different places its concentration ranges from 0% to 4%), solid particles, gases neon, helium, methane, hydrogen, krypton, ozone and xenon. The science that studies the atmosphere is called meteorology.

Life on Earth would not be possible without the presence of an atmosphere, which supplies the oxygen we need to breathe. In addition, the atmosphere performs another important function - it equalizes the temperature throughout the planet. If there were no atmosphere, then in some places on the planet there could be sizzling heat, and in other places extreme cold, the temperature range could fluctuate from -170°C at night to +120°C during the day. The atmosphere also protects us from harmful radiation from the Sun and space, absorbing and dispersing it.

Of the total amount of solar energy reaching the Earth, approximately 30% is reflected by clouds and the earth's surface back into space. The atmosphere absorbs approximately 19% of the sun's radiation, and only 51% is absorbed by the Earth's surface.

Air has weight, although we are not aware of it and do not feel the pressure of the air column. At sea level, this pressure is one atmosphere, or 760 mmHg (1013 millibars or 101.3 kPa). As altitude increases, atmospheric pressure decreases rapidly. The pressure drops 10 times with every 16 km increase in altitude. This means that at a pressure of 1 atmosphere at sea level, at an altitude of 16 km the pressure will be 0.1 atm, and at an altitude of 32 km - 0.01 atm.

The density of the atmosphere in its lowest layers is 1.2 kg/m3. Each cubic centimeter of air contains approximately 2.7 * 10 19 molecules. At ground level, each molecule moves at about 1,600 km/h, colliding with other molecules 5 billion times per second.

Air density also decreases rapidly with increasing altitude. At an altitude of 3 km, air density decreases by 30%. People living near sea level experience temporary breathing problems when raised to such a height. The highest altitude at which people permanently live is 4 km.

The structure of the atmosphere

The atmosphere consists of different layers, the division into these layers occurs according to their temperature, molecular composition and electrical properties. These layers do not have clearly defined boundaries; they change seasonally, and in addition, their parameters change at different latitudes.

Division of the atmosphere into layers depending on their molecular composition

Homosphere

• The lower 100 km, including the Troposphere, Stratosphere and Mesopause.
• Makes up 99% of the mass of the atmosphere.
• Molecules are not separated by molecular weight.
• The composition is fairly homogeneous, with the exception of some small local anomalies. Homogeneity is maintained by constant mixing, turbulence and turbulent diffusion.
• Water is one of two components that are unevenly distributed. As water vapor rises, it cools and condenses, then returning to the ground in the form of precipitation - snow and rain. The stratosphere itself is very dry.
• Ozone is another molecule whose distribution is uneven. (Read below about the ozone layer in the stratosphere.)

Heterosphere

• Extends above the homosphere and includes the Thermosphere and Exosphere.
• The separation of molecules in this layer is based on their molecular weights. Heavier molecules such as nitrogen and oxygen are concentrated at the bottom of the layer. Lighter ones, helium and hydrogen, predominate in the upper part of the heterosphere.

Division of the atmosphere into layers depending on their electrical properties.

Neutral atmosphere

• Below 100 km.

Ionosphere

• Approximately above 100 km.
• Contains electrically charged particles (ions) produced by absorption of ultraviolet light
• The degree of ionization changes with altitude.
• Different layers reflect long and short radio waves. This allows radio signals traveling in a straight line to bend around the spherical surface of the earth.
• Auroras occur in these atmospheric layers.
• Magnetosphere is the upper part of the ionosphere, extending to approximately 70,000 km altitude, this altitude depends on the intensity of the solar wind. The magnetosphere protects us from high-energy charged particles from the solar wind by keeping them in the Earth's magnetic field.

Division of the atmosphere into layers depending on their temperatures

Top border height troposphere depends on seasons and latitude. It extends from the earth's surface to an altitude of approximately 16 km at the equator, and to an altitude of 9 km at the North and South Poles.

• The prefix "tropo" means change. Changes in the parameters of the troposphere occur due to weather conditions - for example, due to the movement of atmospheric fronts.
• As altitude increases, the temperature drops. Warm air rises, then cools and falls back to Earth. This process is called convection, it occurs as a result of the movement of air masses. Winds in this layer blow predominantly vertically.
• This layer contains more molecules than all other layers combined.

Stratosphere- extends from approximately 11 km to 50 km altitude.

• Has a very thin layer of air.
• The prefix "strato" refers to layers or division into layers.
• The lower part of the Stratosphere is quite calm. Jet aircraft often fly into the lower stratosphere to avoid bad weather in the troposphere.
• At the top of the Stratosphere there are strong winds known as high-altitude jet streams. They blow horizontally at speeds of up to 480 km/h.
• The stratosphere contains the "ozone layer", located at an altitude of approximately 12 to 50 km (depending on latitude). Although the concentration of ozone in this layer is only 8 ml/m 3, it is very effective at absorbing harmful ultraviolet rays from the sun, thereby protecting life on earth. The ozone molecule consists of three oxygen atoms. The oxygen molecules we breathe contain two oxygen atoms.
• The stratosphere is very cold, with a temperature of approximately -55°C at the bottom and increasing with altitude. The increase in temperature is due to the absorption of ultraviolet rays by oxygen and ozone.

Mesosphere- extends to altitudes of approximately 100 km.

• As altitude increases, the temperature rises rapidly.

Thermosphere- extends to altitudes of approximately 400 km.

• As altitude increases, the temperature increases rapidly due to the absorption of very short wavelength ultraviolet radiation.
• Meteors, or "shooting stars", begin to burn up at altitudes of approximately 110-130 km above the Earth's surface.

Exosphere- extends for hundreds of kilometers beyond the Thermosphere, gradually moving into outer space.

• The air density here is so low that the use of the concept of temperature loses all meaning.
• When molecules collide with each other, they often fly off into space.

Why is the color of the sky blue?

Visible light is a type of energy that can travel through space. Light from the Sun or an incandescent lamp appears white, although in reality it is a mixture of all colors. The primary colors that make up white are red, orange, yellow, green, blue, indigo and violet. These colors continuously transform into one another, so in addition to the primary colors there are also a huge number of various shades. All these colors and shades can be observed in the sky in the form of a rainbow that appears in an area of ​​high humidity.

The air that fills the entire sky is a mixture of tiny gas molecules and small solid particles such as dust.

As sunlight passes through the air, it encounters molecules and dust. When light collides with gas molecules, light can be reflected in different directions. Some colors, such as red and orange, reach the observer directly by passing directly through the air. But most blue light is reflected from air molecules in all directions. This scatters blue light throughout the sky and makes it appear blue.

When we look up, some of this blue light reaches our eyes from all over the sky. Since we see blue everywhere above our heads, the sky looks blue.

There is no air in outer space. Since there are no obstacles from which the light could be reflected, the light travels directly. The rays of light are not scattered, and the “sky” appears dark and black.

Experiments with light

The first experiment is the decomposition of light into a spectrum

To conduct this experiment you will need:

• a small mirror, a piece of white paper or cardboard, water;
• a large shallow vessel such as a cuvette or bowl, or a plastic ice cream box;
• sunny weather and a window facing the sunny side.

How to conduct an experiment:

1. Fill the cuvette or bowl 2/3 full with water and place it on the floor or table so that direct sunlight reaches the water. The presence of direct sunlight is mandatory for proper experimentation.
2. Place the mirror underwater so that the sun's rays fall on it. Hold a piece of paper over the mirror so that the rays of the sun reflected by the mirror fall on the paper; if necessary, adjust their relative position. Observe the color spectrum on paper.

What happens: The water and mirror act like a prism, splitting light into the color components of the spectrum. This happens because light rays, passing from one medium (air) to another (water), change their speed and direction. This phenomenon is called refraction. Different colors are refracted differently, violet rays are more inhibited and change their direction more strongly. Red rays slow down and change direction less. Light is separated into its component colors and we can see the spectrum.

Second experiment - modeling the sky in a glass jar

Materials required for the experiment:

• a transparent tall glass or a transparent plastic or glass jar;
• water, milk, teaspoon, flashlight;
• a dark room;

Conducting the experiment:

1. Fill a glass or jar 2/3 full with water, approximately 300-400 ml.
2. Add 0.5 to one spoon of milk to the water, shake the mixture.
3. Taking a glass and a flashlight, go into a dark room.
4. Hold a flashlight over a glass of water and direct the light beam at the surface of the water, look at the glass from the side. In this case, the water will have a bluish tint. Now point the flashlight at the side of the glass, and look at the beam of light from the other side of the glass, so that the light passes through the water. In this case, the water will have a reddish tint. Place a flashlight under the glass and direct the light upward, while looking at the water from above. In this case, the reddish tint of the water will look more saturated.

What happens in this experiment is that small particles of milk suspended in water scatter the light coming from a flashlight in the same way that particles and molecules in the air scatter sunlight. When a glass is illuminated from above, the water appears bluish due to the fact that the blue color is scattered in all directions. When you look directly at the light through the water, the light from the lantern appears red because some of the blue rays have been removed due to light scattering.

Third experiment - mixing colors

You will need:

• pencil, scissors, white cardboard or piece of whatman paper;
• colored pencils or markers, ruler;
• a mug or large cup with a diameter at the top of 7...10 cm or a caliper.
• Paper cup.

How to conduct an experiment:

1. If you don't have a caliper, use a mug as a template to draw a circle on a piece of cardboard and cut out the circle. Using a ruler, divide the circle into 7 approximately equal sectors.
2. Color these seven sectors in the colors of the main spectrum - red, orange, yellow, green, blue, indigo and violet. Try to paint the disc as neatly and evenly as possible.
3. Make a hole in the middle of the disk and place the disk on a pencil.
4. Make a hole in the bottom of the paper cup, the diameter of the hole should be slightly larger than the diameter of the pencil. Turn the cup upside down and insert a pencil with a mounted disk into it so that the pencil lead rests on the table, adjust the position of the disk on the pencil so that the disk does not touch the bottom of the cup and is above it at a height of 0.5..1.5 cm.
5. Quickly spin the pencil and look at the rotating disk, pay attention to its color. If necessary, adjust the disk and pencil so that they can rotate easily.

Explanation of the phenomenon seen: the colors with which the sectors on the disk are painted are the main components of the colors of white light. When the disk spins fast enough, the colors seem to merge and the disk appears white. Try experimenting with other color combinations.

The world around us is full of amazing wonders, but we often do not pay attention to them. Admiring the clear blue of the spring sky or the bright colors of the sunset, we don’t even think about why the sky changes color as the time of day changes.


We are accustomed to the bright blue on a fine sunny day and to the fact that in the fall the sky becomes hazy gray, losing its bright colors. But if you ask a modern person why this happens, the vast majority of us, once armed with school knowledge of physics, are unlikely to be able to answer this simple question. Meanwhile, there is nothing complicated in the explanation.

What is color?

From the school physics course we should know that differences in the color perception of objects depend on the wavelength of light. Our eye is able to distinguish only a fairly narrow range of wave radiation, with the shortest waves being blue and the longest being red. Between these two primary colors lies our entire palette of color perception, expressed by wave radiation in different ranges.

A white ray of sunlight actually consists of waves of all color ranges, which is easy to see by passing it through a glass prism - you probably remember this school experience. In order to remember the sequence of changes in wavelengths, i.e. sequence of colors of the daylight spectrum, a funny phrase about a hunter was invented, which each of us learned at school: Every Hunter Wants to Know, etc.


Since red light waves are the longest, they are less susceptible to scattering when passing through. Therefore, when you need to visually highlight an object, they use predominantly red color, which is clearly visible from afar in any weather.

Therefore, a prohibitory traffic light or any other danger warning light is red, not green or blue.

Why does the sky turn red at sunset?

In the evening hours before sunset, the sun's rays fall on the surface of the earth at an angle, and not directly. They have to overcome a much thicker layer of atmosphere than in the daytime, when the surface of the earth is illuminated by the direct rays of the Sun.

At this time, the atmosphere acts as a color filter, which scatters rays from almost the entire visible range, except for red ones - the longest and therefore most resistant to interference. All other light waves are either scattered or absorbed by particles of water vapor and dust present in the atmosphere.

The lower the Sun falls relative to the horizon, the thicker the layer of atmosphere the light rays have to overcome. Therefore, their color is increasingly shifting towards the red part of the spectrum. A folk superstition is associated with this phenomenon, saying that a red sunset foretells a strong wind the next day.


The wind originates in high layers of the atmosphere and at a great distance from the observer. Oblique rays of the sun highlight the emerging zone of atmospheric radiation, in which there is much more dust and vapor than in a calm atmosphere. Therefore, before a windy day we see a particularly red, bright sunset.

Why is the sky blue during the day?

Differences in light wavelengths also explain the clear blue of the daytime sky. When the sun's rays fall directly on the surface of the earth, the layer of atmosphere they overcome has the smallest thickness.

Scattering of light waves occurs when they collide with the molecules of gases that make up the air, and in this situation, the short-wavelength light range turns out to be the most stable, i.e. blue and violet light waves. On a fine, windless day, the sky acquires amazing depth and blueness. But why do we then see blue and not violet in the sky?

The fact is that the cells in the human eye that are responsible for color perception perceive blue much better than violet. Still, violet is too close to the border of the perception range.

This is why we see the sky bright blue if there are no scattering components in the atmosphere other than air molecules. When a sufficiently large amount of dust appears in the atmosphere - for example, in a hot summer in the city - the sky seems to fade, losing its bright blue.

Gray sky of bad weather

Now it’s clear why autumn bad weather and winter slush make the sky hopelessly gray. A large amount of water vapor in the atmosphere leads to the scattering of all components of a white light beam without exception. Light rays are crushed into tiny droplets and water molecules, losing their direction and mixing throughout the entire range of the spectrum.


Therefore, light rays reach the surface as if passed through a giant scattering lampshade. We perceive this phenomenon as the grayish-white color of the sky. As soon as moisture is removed from the atmosphere, the sky again becomes bright blue.