What makes the sky blue. Why the sky is blue? Why is the sunset red? Dividing the atmosphere into layers depending on their molecular composition

Probably everyone at least once in their life faced this simple question: Why is the clear, cloudless sky blue or blue? Obviously because of the air we breathe, because of the Earth's atmosphere! Probably, our air is "blue" or something like that. It only seems transparent, but at long distances planes, mountains, ships seem to be in a bluish haze ... Such reasoning does not remove the main question: why is the sky blue? The air is not painted with blue paint!

The simple and short answer is: the sky is blue because air molecules scatter Blue colour There is more sun than red.

Since the air scatters blue, the sky appears blue and the Sun itself appears yellow. Moreover, at sunset, when sunlight passes through a greater thickness of the atmosphere, we see Red sun and a yellow-red dawn. All this is possible only because blue light is scattered by the atmosphere on its way to us.

But where did the blue light come from? To begin with, the white light from the Sun is a mixture of all the colors of the rainbow, from purple to red. Stop, you say is the light of the sun white? Yes, . Second point: we are now talking about light, not about color... If you mix paints different colors then we will, of course, get something almost black.

The color of light is not the color of any object. If we mix about equal amounts of red, yellow, orange, green, cyan, blue and violet light, we get white light. Isaac Newton was the first to demonstrate this, using a prism to separate different colors and form a spectrum.

Scientists have found that colored light is just light of different wavelengths. The visible part of the spectrum ranges from red light with a wavelength of about 720 nm to violet with a wavelength of about 380 nm, between which are orange, yellow, green, cyan and blue colors. Three different types of color receptors in the retina of the human eye react most strongly to red, green and blue wavelengths, giving us all the variety of colors.

Yes, so what does physics say about why the sky is blue?

Tyndall effect

The first steps towards the correct explanation of the color of the sky were made John Tyndall in 1859. He discovered an interesting effect: if you pass light through a transparent liquid in which small particles are suspended, then blue light will be scattered by these particles more strongly than red light.

This can be easily demonstrated. Take a glass of water and stir in it a few drops of milk, some flour or soap, so that the water in the glass becomes cloudy. Then pass the light of a flashlight through the glass. You will see that the light inside the glass has become bluish... Rather, the light that got into your eyes from the glass became bluish, that is, it was deflected and scattered in the solution!

But the most interesting thing is that the light at the exit from the glass, having lost some of its blue component, will no longer be white, but yellowish! If you take a sufficiently wide container, then the light, repeatedly scattered on the road, will finally lose the blue component and come out of the container not yellow, but red.

The Tyndall effect concerns the scattering of light in turbid liquids. Particles in such a liquid must have a special surface structure - grooves, lattices, pores, angles, the size of which is comparable to the length of the light wave.

Thanks to the Tyndall effect, there are beautiful blue sapphirinid crustaceans. These tiny, as if glowing from within, animals sometimes become completely invisible to the observer (light scattering goes into the ultraviolet region) ...

The Tyndall effect is also responsible for blue eyes in humans!

Yes, yes, blue eyes are not created by blue pigment at all - it is simply not there - but melanin that scatters light appropriately!

Several years later, the Tyndall effect was studied in detail by Lord Rayleigh. Since then, the scattering of light by very small particles has become known as Rayleigh scattering... Rayleigh showed that the amount of scattered light is inversely proportional to the fourth power of the wavelength for sufficiently small particles. From this it follows that blue light is scattered on such particles more than red, about 10 times: (700 nm / 400 nm) 4 = 10

Dust or Molecules?

All this is wonderful, but our sky is filled with air, not liquid, and there are no pieces of soap or milk floating in the sky ... What are the particles that scatter light in the air? Tyndall and Rayleigh believed that the blue sky must be due to fine dust particles and water vapor droplets suspended in the atmosphere just like milk particles suspended in water.

This is a misconception, although some people today say that the color of the sky is determined by steam and dust. If this were the case, then the color of the sky would change much more depending on humidity or fog than it actually does. Therefore, scientists assumed (correctly!) That oxygen and nitrogen molecules are sufficient to explain the scattering. This is the air itself, or rather, its molecules scatter light!

Blue sky and clouds on it. Air scatters light according to Rayleigh scattering, and larger cloud particles according to Mie scattering. Photo: Andrei Azanfirei / Flickr.com

The question was finally solved by Albert Einstein in 1911, who calculated a detailed formula for the scattering of light depending on molecules and further experiments brilliantly confirmed his calculations. They say that Einstein was even able to use his calculations as an additional test of Avogadro's number!

Why is the sky blue and not purple?

By the way, if blue light is scattered 10 times more than red, then even shorter violet waves should scatter more than blue! The question arises: why doesn't the sky look purple?

First, the spectrum of light emission from the sun is not the same at all wavelengths - the maximum energy in the sun's spectrum falls on green light. Secondly, short-wave violet light is actively absorbed in the upper atmosphere (like ultraviolet light!), So less violet than blue reaches the Earth's surface.

Finally, the third reason is our eyes less sensitive to violet light than blue.

Sensitivity curves for three types of cones in the human eye.

We have three types of color receptors, or cones, in the retina. They are called reds, blues and greens because they react most strongly to light at these wavelengths. But in fact, they are able to capture light of other wavelengths, covering the entire spectrum.

When we look at the sky, red cones respond to a small amount of scattered red light, but also less strongly to orange and yellow wavelengths. Green cones respond to yellow and more highly diffuse green and green-blue waves. Finally, blue cones are stimulated by blue wavelength colors, which are highly scattered. If there were no blue and violet in the spectrum, the sky would appear blue with a slight greenish tint. But the most strongly scattered waves of blue and violet lightly stimulate the red cones, so these colors appear blue with an added red tint. The overall effect is that when we look at the sky, red and green cones are stimulated in about the same way and the blue ones are more stimulated. This combination ultimately forms a blue or blue sky.

Beautiful sunsets

What could be more beautiful than quiet sunsets on the seashore or in the steppe? When the air is clear and clear, the sunset will be yellow, just like a flashlight beam crossing a glass of soap solution: some of the blue light will scatter and the overall color of the Sun will shift towards the red end of the spectrum.

Sunsets can be extremely varied in color depending on the state of the atmosphere. Photo: Alex Derr

It's another matter if the air is polluted with small particles - smoke, dust, smog. In this case, the sunset will be orange and even red. Sunsets over the sea can also be orange due to salt particles suspended in the air, which can create a Tyndall effect. The sky around the sun is seen reddened, as well as light coming directly from the sun. This is because all light is scattered relatively well at small angles, but then blue light is more likely to be scattered twice or more at large distances, leaving yellow, red and orange colors.

Clouds, blue moon and blue haze

Clouds and dusty haze appear white because they are composed of particles of long wavelengths of light. Such particles will equally scatter all wavelengths (Mie scattering).

But sometimes there can be much smaller particles in the air. Some mountainous areas are famous for their blue haze. Terpene aerosols from vegetation react with ozone in the atmosphere to form small particles with a diameter of about 200 nm, which are excellent at scattering blue light.

Blue haze over the Bay of Kotor in Montenegro. Photo: Rocher / Flickr.com

A forest fire or volcanic eruption can sometimes fill the atmosphere with fine particles 500-800 nm in diameter, which is a suitable size for scattering red light. This is the opposite of the usual Tyndall effect and can cause the Moon to take on a blue tint, as the red light from the Moon is scattered by these particles. The present blue Moon- a very rare occurrence!

Why is the sky of Mars red?

So we got to Mars, the sky on which, judging by the images of Mars rovers and automatic descent vehicles, is now red, sometimes sandy-yellow, sometimes grayish-blue ... What is it really like?

According to physics, the Martian sky should be blue. It and there is blue, but only when the atmosphere on the Red Planet is calm. However, on Mars, as you know, winds often blow. Despite the fact that the atmosphere of the planet is extremely rarefied, winds are capable of lifting millions of tons of sand and dust to create real sandstorms. Some storms can hide almost the entire surface of Mars!

After such storms, particles of iron-rich dust remain suspended in the air for a long time. The color of this dust is red (this is rust), respectively, and the sky on Mars turns yellowish-orange.

Reflection nebulae

Finally, let's look far into space, where stars are now being born.

The complex of nebulae ro Ophiuchus. Photo: Jim Misti / Steve Mazlin / Robert Gendler

Here is a whole complex of cosmic gas and dust clouds located on the border of the constellations Ophiuchus and Scorpio. Pay attention: some of the clouds glow brightly with a reddish glow, the other part, on the contrary, absorbs light and resembles black dips. Finally, the third part is bluish in color.

All three types of clouds are composed primarily of hydrogen with a small amount of dust and molecules. Why do they look different? It's all about their temperature. Heated by the light of the stars immersed in them, the clouds begin to glow themselves. The red glow is hydrogen emission. Very cold clouds, on the other hand, absorb light and are therefore opaque to us. Finally, cold, but located close to bright stars the clouds look bluish. They are reflect the light of the stars, scattering it just like the atmosphere of the Earth!

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One of distinctive features human is curiosity. Probably everyone, as a child, looked at the sky and wondered: "Why is the sky blue?" As it turns out, the answers to these seem to be simple questions require some knowledge base in the field of physics, and therefore not every parent will be able to correctly explain to the child the reason for this phenomenon.

Let's consider this issue from a scientific point of view.

The wavelength range of electromagnetic radiation covers almost the entire spectrum of electromagnetic radiation, which includes radiation visible to humans. The image below shows the dependence of the intensity of solar radiation on the wavelength of this radiation.

Analyzing this image, it can be noted that the visible radiation is also represented by uneven intensity for radiation of different wavelengths. So a relatively small contribution to visible radiation is made by violet, and the largest - by blue and green.

Why the sky is blue?

First of all, this question is prompted by the fact that air is a colorless gas and should not emit blue light. It is obvious that our star is the cause of such radiation.

As you know, white light is actually a combination of radiation of all colors of the visible spectrum. With the help of a prism, it is possible to clearly expand the light into the entire color range. A similar effect occurs in the sky after rain and forms a rainbow. When sunlight enters the earth's atmosphere, it begins to scatter, i.e. radiation changes its direction. However, the peculiarity of the composition of air is such that when light enters it, radiation with a short wavelength is scattered more strongly than long-wavelength radiation. Thus, taking into account the spectrum shown earlier, it can be seen that the red and orange light will practically not change their trajectories, passing through the air, while the violet and blue radiation will noticeably change their direction. For this reason, a kind of "wandering" short-wavelength light appears in the air, which is constantly scattered in this environment. As a result of the described phenomenon, it seems that shortwave radiation of the visible spectrum (violet, blue, blue) is emitted at every point in the sky.

The well-known fact of perception of radiation is that the human eye can catch, see, radiation only if it has directly entered the eye. Then, looking into the sky, you will most likely see the shades of the visible radiation, the wavelength of which is the smallest, since it is it that is scattered in the air best of all.

Why, looking at the Sun, you do not see a distinctly red color? First, it is unlikely that a person will be able to carefully examine the Sun, since intense radiation can damage the visual organ. Secondly, despite the existence of such a phenomenon as the scattering of light in the air, nevertheless, most of the light emitted by the Sun reaches the surface of the Earth without being scattered. Therefore, all the colors of the visible spectrum of radiation are combined, forming light with a more pronounced white color.

Let's return to the light scattered by air, the color of which, as we have already determined, should have the shortest wavelength. Of the visible radiation, violet has the smallest wavelength, followed by blue, and slightly longer than the wavelength it has blue. Taking into account the uneven intensity of the Sun's radiation, it becomes clear that the contribution of the violet color is negligible. Therefore, the blue color makes the greatest contribution to the radiation scattered by air, followed by blue.

Why is the sunset red?

In the case when the Sun is hiding behind the horizon, we can observe the same long-wavelength red-orange radiation. In this case, the light from the Sun should pass noticeably greater distance in the Earth's atmosphere before reaching the eye of the observer. In the place where the sun's radiation begins to interact with the atmosphere, the most pronounced colors are blue and blue. However, with distance, shortwave radiation loses its intensity, as it is significantly scattered along the way. Whereas long-wavelength radiation does an excellent job of covering such long distances. This is why the Sun is red at sunset.

As mentioned earlier, although long-wave radiation is weakly scattered in air, there is still scattering. Therefore, being on the horizon, the Sun emits light, from which only the radiation of red-orange shades reaches the observer, which somewhat manages to dissipate in the atmosphere, forming the previously mentioned "wandering" light. The latter paints the sky in variegated shades of red and orange.

Why are the clouds white?

Clouds are known to be composed of microscopic droplets of liquid that scatter visible light almost evenly, regardless of the wavelength of the radiation. Then the scattered light directed in all directions from the droplet is scattered again on other droplets. In this case, the combination of radiation of all wavelengths is preserved, and the clouds "glow" (reflected) in white.

If the weather is cloudy, then solar radiation reaches the surface of the Earth in small quantities. In the case of large clouds, or a large number of them, some of the sunlight is absorbed, so the sky dims and takes on a gray color.

Looking at the sky on a fine day, from childhood we get used to its blue color during the day and scarlet at sunset and sunrise. The blue color of the sky is so familiar to our eyes that often there is no question why the color of the sky is blue, and not, for example, green or yellow. Indeed, why is the sky blue, if the main source of light for the Earth is the Sun, which shines with yellow light? (Just do not rush to check what color the Sun is, without eye protection).

What color is the sun really?

It turns out that the light coming from the Sun has different colors. In fact, the Sun shines with blue, green, yellow, and red light. It was discovered back in the 17th century by Newton. We see the Sun as yellow, because it emits the yellow color the most, and we can see the rest of the colors only with the help of special equipment. The yellow light is so intense that a person cannot distinguish other colors in its background. It's like trying to spot a small green or blue flashlight in front of a huge yellow spotlight.

How does light hit the surface of the Earth?

Imagine rays of all colors of the rainbow going from the Sun to the Earth. In the vacuum of space, between the Sun and the Earth, the sun's rays fly in the same direction and at the same speed. But everything changes when the light of the Sun reaches the earth's atmosphere. The sun's rays collide with air molecules (consisting mainly of oxygen and nitrogen) and change their direction - they scatter. Let's observe the process of light scattering. Here is a small "piece" of sunlight - a photon that flies into the Earth's atmosphere; and immediately some air molecule gets in its way. The photon "touches" this molecule and deviates slightly from the original path. Having flown a little more, the photon will again collide with an air molecule and again change direction. Until such a "bully-traveler" reaches our eye, he will have time to collide with billions of molecules and change the direction of movement about the same number of times. Light passing through the earth's atmosphere changes its direction so much that photons begin to move in all directions, even towards the Sun. That is why during the day the sky is bright even from the side opposite to the Sun.

Why the sky is blue?

It turns out that the color of light greatly affects the ability of individual "pieces of light" to change their direction after colliding with air molecules. The bluer the light, the more readily it changes the direction of its movement when scattered in the atmosphere. This means that blue light is scattered the best, and turquoise is already a little worse. Green and yellow lights change direction worse than turquoise. Well, least of all, when passing through the atmosphere, the red light changes its direction. It dissipates about 10 times worse than blue. Therefore, it turns out that the blue light coming from the Sun is scattered throughout the sky, and it seems to us that the sky becomes blue. If nature was arranged in a different way, and, for example, green light would be best scattered, then our sky would be green.

Why does the sky turn red at sunset and sunrise?

When the sun sets or rises, the sunlight has to pass through a thicker layer of air before reaching our eyes. This means that photons hitting the Earth at sunset or sunrise will experience many more collisions with air molecules than those that hit the Earth during the day. The increased number of collisions leads to the fact that even red light begins to scatter, so the sky next to the sun turns scarlet at sunset or sunrise.

Konstantin Kudinov

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We are all accustomed to the fact that the color of the sky is a fickle characteristic. Fog, clouds, time of day - everything affects the color of the dome over your head. Its daily change does not occupy the minds of most adults, which cannot be said about children. They are constantly wondering why the sky is blue in terms of physics, or what colors the sunset red. Let's try to understand these not the easiest questions.

Changeable

It is worth starting with an answer to the question of what, in fact, the sky is. IN ancient world it really was seen as a dome covering the Earth. Today, however, hardly anyone does not know that, no matter how high the curious explorer ascends, he will not be able to reach this dome. The sky is not a thing, but rather a panorama that opens when viewed from the surface of the planet, a kind of appearance woven of light. Moreover, if you observe from different points, it may look different. So, from the one rising above the clouds, a completely different view opens than from the ground at this time.

The clear sky is blue, but as soon as the clouds come in, it turns gray, leaden, or off-white. The night sky is black, sometimes you can see reddish areas on it. This is a reflection of the city's artificial lighting. The reason for all such changes is light and its interaction with air and particles of various substances in it.

The nature of color

In order to answer the question of why the sky is blue from the point of view of physics, you need to remember what color is. This is a wave of a certain length. The light coming from the Sun to the Earth is seen as white. Even from Newton's experiments, it is known that it is a bundle of seven rays: red, orange, yellow, green, light blue, blue and violet. Colors differ in wavelength. The red-orange spectrum includes the most impressive waves in this parameter. parts of the spectrum are characterized by a short wavelength. The decomposition of light into a spectrum occurs when it collides with molecules of various substances, while part of the waves can be absorbed, and part - scattered.

Investigating the cause

Many scientists have tried to explain why the sky is blue in terms of physics. All researchers sought to find a phenomenon or process that scatters light in the planet's atmosphere in such a way that as a result, only blue reaches us. Water was also the first candidate for the role of such particles. It was believed that they absorb red light and transmit blue, and as a result, we see the blue sky. Subsequent calculations, however, showed that the amount of ozone, ice crystals and water vapor molecules in the atmosphere was not enough to give the sky a blue color.

The reason is pollution

At the next stage of research, John Tyndall suggested that dust plays the role of the desired particles. Blue light has the greatest resistance to scattering, and therefore is able to pass through all layers of dust and other suspended particles. Tyndall conducted an experiment that confirmed his assumption. He created a model of a smog in a laboratory and illuminated it with bright white light. The smog took on a blue hue. The scientist made an unambiguous conclusion from his research: the color of the sky is determined by dust particles, that is, if the air of the Earth were clean, then not blue, but white skies shone above the heads of people.

Lord's research

The final point on the question of why the sky is blue (from the point of view of physics) was put by the English scientist, Lord D. Rayleigh. He proved that it is not dust or smog that colors the space overhead in the shade we are used to. It's about the air itself. Gas molecules absorb the largest and primarily the longest wavelengths, equivalent to red. In this case, the blue is scattered. This is how the color of the sky we see in clear weather is explained today.

The attentive will notice that, following the logic of scientists, the dome over your head should be purple, since it is this color that has the shortest wavelength in the visible range. However, this is not a mistake: the proportion of violet in the spectrum is much less than that of blue, and human eyes are more sensitive to the latter. In fact, the blue we see is the result of mixing blue with purple and some other colors.

Sunsets and clouds

Everyone knows that at different times of the day you can see different colors of the sky. Photos of beautiful sunsets over the sea or lake are a great illustration of this. All sorts of shades of red and yellow combined with blue and dark blue make such a spectacle unforgettable. And it is explained by the same scattering of light. The fact is that during dusk and dawn, the sun's rays have to overcome a much larger path through the atmosphere than during the height of the day. In this case, the light of the blue-green part of the spectrum is scattered in different directions and the clouds located at the horizon line become colored in shades of red.

When the sky is covered with clouds, the picture changes completely. unable to overcome the dense layer, and most of them simply do not reach the ground. The rays that have managed to pass through the clouds meet with water drops of rain and clouds, which again distort the light. As a result of all these transformations, white light reaches the earth, if the clouds are small in size, and gray, when the sky is covered by impressive clouds, which again absorb part of the rays.

Other heaven

I wonder what on other planets Solar system when viewed from the surface, you can see the sky, which is very different from the earth. On the space objects deprived of the atmosphere, the sun's rays freely reach the surface. As a result, the sky here is black, without any shade. Such a picture can be seen on the Moon, Mercury and Pluto.

The Martian sky has a reddish-orange hue. The reason for this lies in the dust with which the atmosphere of the planet is saturated. It is painted in different shades of red and orange. When the Sun rises above the horizon, the Martian sky turns pinkish-red, while the portion of it directly surrounding the luminary's disk appears blue or even purple.

The sky above Saturn is the same color as on Earth. Aquamarine skies stretch over Uranus. The reason lies in the methane haze located in the upper planets.

Venus is hidden from the eyes of researchers by a dense layer of clouds. It does not allow the rays of the blue-green spectrum to reach the planet's surface, so the sky here is yellow-orange with a gray stripe along the horizon.

Exploring overhead space during the day reveals no less wonders than exploring the starry sky. Understanding the processes taking place in the clouds and behind them helps to comprehend the reason for things that are quite familiar to the average person, which, nevertheless, not everyone can explain right off the bat.

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

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

Atmosphere

The atmosphere is a mixture of gases and other particles that surround the earth. The atmosphere is mainly composed of gaseous nitrogen (78%) and oxygen (21%). 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 contains small amounts of other gases, as well as the smallest 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 heavy 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 a low altitude near the Earth's surface is the highest; with increasing altitude, it gradually decreases. There is no clear-cut boundary between the atmosphere and space.

Light waves

Light is a type of energy that is carried by waves. In addition to light, with the help of waves, other types of energy are transferred, for example, sound wave is the vibrations of the 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.

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

Visible light colors

Visible light is part of the electromagnetic spectrum that can be seen with our eyes. The light emitted by the sun or incandescent lamp may have White color but in reality it is a mixture of different colors. You can see the different colors of the visible spectrum of light by decomposing it with a prism. This spectrum can also be observed in the sky as a rainbow, arising from the refraction of the sun's light in water droplets acting as one giant prism.

The colors of the spectrum are mixed, continuously passing one into the other. At one end, the spectrum is red or orange. These colors fade into yellow, green, blue, indigo and purple colors... Colors have different wavelengths, different frequencies, and differ in energy.

Spreading light in the 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 propagate in a straight line until there is dust or gas molecules in its path. 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 collides with these large particles. Different colors of visible light are equally reflected by these particles. Reflected light appears to be white because it still contains the same colors that were in it before the reflection.

Gas molecules are smaller than the wavelength of visible light. If a light wave collides with them, then 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 emitted light is the same color that was absorbed. But colors of different wavelengths are absorbed in different ways. Any color can be absorbed, but higher frequencies (cyan) 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 the light moves through the atmosphere, most long waves the optical spectrum passes unchanged. Only a small fraction of the red, orange and yellow colors interact with air.

However, many of the shorter wavelengths of light are absorbed by gas molecules. Once absorbed, blue is emitted in all directions. It scatters everywhere in the sky. Whichever direction you look in, some of this scattered blue light reaches the observer. Since blue light is visible everywhere overhead, the sky looks blue.

If you look towards the horizon, the sky will have a paler hue. This is the result of light travels a greater distance in the atmosphere to the observer. The scattered light is again scattered by the atmosphere and less blue 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, then the Sun would appear to us to be white. There is no atmosphere in space that scatters sunlight. On Earth, some of the short wavelengths of sunlight (blue and violet) are absorbed by scattering. The rest of the spectrum appears in yellow.

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

Why is the sunset red?

When the sun goes down, the 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 to be different, it has a range of colors from orange to red. This is due to the fact that even more shortwave colors, blues and greens, are scattered. Only the long-wavelength components of the optical spectrum remain, which reach the observer's eyes.

The sky around the setting sun can be colored differently. The most beautiful sky is 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 light beams of longer wavelengths are seen by the observer, and therefore the sky appears red, pink, or orange.

Learn 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 gravity of the Earth. 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%), particulate matter, 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 an atmosphere that supplies the oxygen we need to breathe. In addition, the atmosphere has another important function - it evens out the temperature across the planet. If there was no atmosphere, then in some places of the planet there could be an incinerating heat, and in other places it could be extremely cold, the temperature range could range from -170 ° C at night to + 120 ° C during the day. The atmosphere also protects us from the harmful radiation of the Sun and space, absorbing and scattering it.

Of the total amount of energy from the Sun reaching the Earth, approximately 30% is reflected by clouds and the earth's surface back into space. The atmosphere absorbs about 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 we do not feel the pressure of the air column. At sea level, this pressure is one atmosphere, or 760 mm Hg (1013 millibars or 101.3 kPa). With increasing height Atmosphere pressure decreases rapidly. The pressure drops by a factor of 10 with an increase in altitude for every 16 km. 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 / m 3. Each cubic centimeter of air contains approximately 2.7 * 10 19 molecules. At ground level, each molecule moves at a speed of about 1600 km / h, while the frequency of collisions with other molecules is 5 billion times per second.

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

The structure of the atmosphere

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

Dividing the atmosphere into layers depending on their molecular composition

Homosphere

Lower 100 km including Troposphere, Stratosphere and Mesopause.
It makes up 99% of the mass of the atmosphere.
Molecules are not categorized by molecular weight.
The composition is fairly uniform, with the exception of some small local anomalies. Homogeneity is maintained by constant mixing, turbulence and turbulent diffusion.
Water is one of two unevenly distributed components. When water vapor rises upward, 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 that is unevenly distributed. (Read about the ozone layer in the stratosphere below.)

Heterosphere

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

Dividing the atmosphere into layers depending on their electrical properties.

Neutral atmosphere

Below 100 km.

Ionosphere

Above about 100 km.
Contains electrically charged particles (ions) produced by absorbing 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 up to about 70,000 km, this height 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.

Dividing the atmosphere into layers depending on their temperatures

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

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

Stratosphere- stretches from about 11 km to 50 km.

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 planes often fly in the lower Stratosphere to get around bad weather in the Troposphere.
Strong winds known as high-altitude jet streams blow in the upper part of the Stratosphere. They blow horizontally at speeds up to 480 km / h.
The stratosphere contains an "ozone layer" located at an altitude of about 12 to 50 km (depending on latitude). Although the concentration of ozone in this layer is only 8 ml / m3, it absorbs the harmful UV rays of the sun very effectively, 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 temperatures of about -55 ° C at the bottom and increasing with altitude. The increase in temperature is associated with the absorption of ultraviolet rays by oxygen and ozone.

Mesosphere- extends to heights of about 100 km.

With increasing altitude, the temperature rises rapidly.

Thermosphere- extends to heights of about 400 km.

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

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

The air density is so low here 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 sky blue?

Visible light is a form of energy that can travel through space. Light from the sun or an incandescent lamp appears white, when in reality it is a mixture of all colors. The primary colors that make up white are red, orange, yellow, green, cyan, blue and purple. These colors continuously change from one to another, therefore, in addition to the basic colors, there is also a huge number of all kinds of shades. All these colors and shades can be observed in the sky in the form of a rainbow that occurs 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 bumps into 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 of the blue light bounces off air molecules in all directions. Thus, the blue light is scattered throughout the sky and it appears blue.

When we look up, some of this blue light reaches our eyes from all corners of the sky. Since we can see blue all over 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 spreads directly. The light rays are not scattered, and the "sky" looks dark and black.

Experiments with light

The first experiment is the decomposition of light into a spectrum

To carry out 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 overlooking the sunny side.

How to experiment:

Fill a cuvette or bowl 2/3 full with water and place on the floor or table so that direct sunlight reaches the water. The presence of direct sunlight is imperative for the correct experiment.
Place the mirror under the water so that the sun's rays fall on it. Hold a piece of paper above the mirror so that the rays of the sun reflected by the mirror hit the paper, if necessary, adjust their relative position. Observe the color spectrum on paper.

What happens: The water and the mirror act like a prism, breaking down the light into the color spectrum. This is because the rays of light passing from one medium (air) to another (water) change their speed and direction. This phenomenon is called refraction. Different colors are refracted in different ways, violet rays are more inhibited and more strongly change their direction. Red rays slow down and change their direction to a lesser extent. The light is split into its constituent colors and we can see the spectrum.

The 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;

Experiment:

Fill a glass or jar 2/3 full with water, about 300-400 ml.
Add from 0.5 to one spoonful of milk to the water, shake the mixture.
Taking a glass and a flashlight, go into a dark room.
Hold the flashlight over a glass of water and direct a beam of light onto 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 travels through the water. This will give the water a reddish tint. Place a flashlight under a glass and direct the beam of light upward, while looking at the water from above. This will make the reddish tint in the water look more saturated.

What happens in this experiment: Small particles of milk suspended in water scatter the light coming from a flashlight, just like particles and molecules in the air scatter sunlight. When the 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 appears red as some of the blue rays have been removed due to light scattering.

Third experiment - mixing colors

You will need:

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

How to experiment:

If you do not have a caliper, then use the mug as a template to draw a circle on a piece of cardboard, cut out this circle. Use a ruler to divide the circle into 7 roughly equal sectors.
Color these seven sectors with the colors of the main spectrum - red, orange, yellow, green, cyan, blue and violet. Try to color the disc as neatly and evenly as possible.
Punch a hole in the middle of the disc and place the disc on a pencil.
Punch a hole in the bottom of the paper cup, making the hole slightly larger than the pencil. Turn the glass upside down and insert the pencil with the attached disc into it so that the pencil lead rests on the table, adjust the position of the disc on the pencil so that the disc does not touch the bottom of the glass and is above it at a height of 0.5 ... 1.5 cm.
Unroll the pencil quickly and look at the spinning disc, notice its color. If necessary, adjust the dial and pencil so that they can rotate easily.

Explanation of the observed phenomenon: the colors used to color the sectors on the disk are the main components of the colors of white light. When the disc is spinning fast enough, the colors appear to merge and the disc looks white. Try experimenting with other color combinations.