Wears the usual blue color. At night, it turns black. But during sunset, it always turns bright red. Why does this happen, for what reason does the crimson hue spread across the sky? Perhaps, many people have repeatedly asked this question, and therefore it makes sense to give an exhaustive answer to it.

The sunset is tinted with the rays of the setting sun, this is understandable to many. But why is it red, and not orange or another color?

Features of the color spectrum

Before reaching the surface of the earth, where people can contemplate it, sunlight must pass through the entire air shell of the planet. The light has a wide spectrum, in which the primary colors, the shades of the rainbow, still stand out. Of this spectrum, red has the longest wavelength of light, while violet has the shortest. At sunset, the solar disk rapidly turns red and rushes closer to the horizon.

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In this case, the light has to overcome an increasing thickness of air, and part of the waves is lost. Purple disappears first, then blue, blue. The longest waves of red color continue to penetrate to the surface of the Earth to the last, and therefore the solar disk and the halo around it until the last moments have reddish hues.

Why is the sky blue during the day?


Long light waves can penetrate deep into the atmosphere for the reason that they are almost not absorbed, not scattered by aerosols and suspensions that constantly circulate in the planet's atmosphere. When the luminary is closer to the zenith, a different situation develops, which provides the sky with blueness. Blue has shorter wavelengths than red and is absorbed more strongly. But its dispersal ability is 4 times higher compared to red.

When the sun is at or near its zenith, the sky is always blue. This is due to the fact that the layer of air between the planet and the star at this moment is small, and blue, blue waves pass freely. They have a great ability to diffuse, and therefore successfully drown out other colors and shades. Therefore, this color dominates the sky for almost the entire daylight hours.

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What changes in the evening?


Closer to sunset, the Sun rushes to the horizon, the lower it falls, the faster the evening approaches. At such times, the layer of atmosphere that separates the original sunlight from the earth's surface begins to increase dramatically due to the angle of inclination. At some point, the thickening layer ceases to transmit other light waves except red, and at that moment the sky is painted in this color. Blue is no longer present, it is absorbed in the process of passing through the layers of the atmosphere.

: at sunset, the sun and sky pass through a whole gamut of hues as one or the other of them ceases to pass through the atmosphere. The same can be observed at the time of sunrise, the causes of both phenomena are the same.

What happens at sunrise?

At sunrise, the sun's rays go through the same process, but in reverse order. That is, first, the first rays break through the thickness of the atmosphere at a strong angle, only the red spectrum reaches the surface. Therefore, the sunrise initially dawns red. Then, as the sunrise and the angle change, waves of other colors begin to pass - the sky turns orange, and then it becomes habitually blue. A half-day deep blue of the sky is observed, and then, by evening, it begins to turn again to crimson. On one side of the sky, far from the sun, there is a blue-black tint, but the closer to the setting star, the more red shades can be seen near the horizon, until the Sun disappears completely.

From red to purple, which are the main colors of the spectrum. The color seen by the eye is explained by the wavelength of the light. Accordingly, red gives the longest light, and purple the shortest.

During sunset, a person can observe a disk rapidly approaching the horizon. At the same time, sunlight passes through an increasing thickness. The longer the wavelength of light, the less it is subject to absorption by the atmospheric layer and aerosol suspensions present in it. To explain this phenomenon, you need to consider the physical properties of blue and red colors, the usual shades of the sky.

When the sun is at its zenith, the observer can tell that the sky is blue. This is due to differences in the optical properties of blue and red colors, namely the ability to scatter and absorb. Blue is more absorbent than red, but its scattering power is much higher (four times) than that of red. The ratio of wavelength to light intensity is a proven physical pattern called the Rayleigh blue sky law.

When the sun is high, the layer of atmosphere and suspension separating the sky from the observer's eyes is relatively small, the short wave of blue is not completely absorbed, and the high scattering power "muffles" other colors. This is why the sky looks blue during the day.

When the time comes for sunset, the sun begins to rapidly descend to the line of the true horizon, and the layer of the atmosphere increases sharply. After a certain time, the layer becomes so dense that the blue color is almost completely absorbed, and the red color, due to its high resistance to absorption, comes to the fore.

Thus, at sunset, the sky and the luminary itself is seen by the human eye in various shades of red, from orange to bright scarlet. It should be noted that at sunrise the same thing is observed and for the same reasons.

It is nice to look at the dazzling blue sky or enjoy the crimson sunset. Many people enjoy admiring the beauties of the world around them, but not everyone understands the nature of what they observe. In particular, they find it difficult to answer the question why the sky is blue and the sunset is red.

The sun emits pure white light. It seems that the sky should be white, but it is seen as bright blue. Why is this happening?

Scientists for several centuries could not explain the blue color of the sky. From a school course in physics, everything that is white light can be decomposed with the help of a prism into its constituent colors. There is even a simple phrase for them: "Every Hunter Wants to Know Where the Pheasant Sits." The initial words of this phrase allow you to remember the order of colors in: red, yellow, green, blue, indigo, violet.

Scientists have suggested that the blue color of the sky is due to the fact that the blue component of the solar spectrum best reaches the Earth's surface, while other colors are absorbed by ozone or dust scattered in the atmosphere. The explanations were quite interesting, but they were not confirmed by experiments and calculations.

Attempts to explain the blue color of the sky did not stop, and in 1899 Lord Rayleigh put forward a theory that finally gave an answer to this question. It turned out that the blue color of the sky is caused by the properties of air molecules. A certain amount of rays coming from the Sun reach the Earth's surface without interference, but most of them are absorbed by air molecules. By absorbing photons, air molecules are charged (excited) and already emit photons themselves. But these photons have a different wavelength, and photons that give blue color predominate among them. That is why the sky looks blue: the more sunny the day is and the less cloudy, the more saturated this blue color of the sky becomes.

But if the sky is blue, why does it turn crimson at sunset? The reason for this is very simple. The red component of the solar spectrum is much worse absorbed by air molecules than other colors. During the day, the sun's rays enter the Earth's atmosphere at an angle that directly depends on the latitude at which the observer is located. At the equator this angle will be close to a straight line, closer to the poles it will decrease. As the Sun moves, the layer of air that light rays need to pass through before reaching the observer's eye increases - after all, the Sun is no longer overhead, but tends to the horizon. A thick layer of air absorbs most of the rays of the solar spectrum, but the red rays reach the observer almost without loss. That is why the sunset looks red.

On April 26, 2012, strange greenish clouds appeared in the sky over Moscow. The inexplicable phenomenon alarmed the residents of the capital and excited the Russian Internet. It was suggested that an accident occurred at one of the enterprises, which was accompanied by the release of chemicals harmful to health into the atmosphere. Fortunately, the information has not been confirmed.

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The chief sanitary doctor of the Russian Federation, Gennady Onishchenko, said that according to official data, there were no accidents at chemical plants in the Moscow region and nearby regions. Meanwhile, in some areas of Moscow, people really felt worse. Allergy sufferers and asthmatics understood the reason for this abnormal phenomenon.

After a long winter in the first days of April, a sharp warming, which caused a rapid melting of the snow cover, the early blooming of leaves on trees and the flowering of several of their species at once: birch, alder,

Despite scientific progress and free access to many sources of information, a rare person can correctly answer the question why the sky is blue.

Why is the sky blue during the day?

White light - namely, it radiates from the Sun - consists of seven parts of the color spectrum: red, orange, yellow, green, blue, indigo and violet. The counting rhyme known from school - "Every Hunter Wants to Know Where the Pheasant Sits" - just determines the colors of this spectrum by the initial letters of each of the words. Each color has its own wavelength of light: the longest for red and the shortest for purple.

The sky (atmosphere) familiar to us consists of solid microparticles, tiny drops of water and gas molecules. Over time, there have been several misconceptions trying to explain why the sky is blue:

  • the atmosphere, consisting of the smallest particles of water and molecules of various gases, passes the rays of the blue spectrum well and does not allow the rays of the red spectrum to touch the Earth;
  • small solid particles - for example, dust - suspended in the air scatter blue and violet waves the least, and because of this they manage to reach the Earth's surface, unlike other colors of the spectrum.

These hypotheses were supported by many famous scientists, but the studies of the English physicist John Rayleigh showed that it is not solid particles that are the main cause of light scattering. It is the molecules of gases in the atmosphere that separate the light into color components. A white sunbeam, colliding with a gas particle in the sky, scatters (scatters) in different directions.

When colliding with a gas molecule, each of the seven color components of white light is scattered. In this case, light with longer wavelengths (the red component of the spectrum, which also includes orange and yellow) is scattered worse than light with short waves (the blue component of the spectrum). Because of this, after scattering, eight times more blue spectrum colors remain in the air than red ones.

Although violet has the shortest wavelength, the sky still appears blue due to the mixture of violet and green wavelengths. In addition, our eyes perceive blue better than purple, with the same brightness of both. It is these facts that determine the color scheme of the sky: the atmosphere is literally filled with blue-blue rays.

Why is the sunset red then?

However, the sky is not always blue. The question naturally arises: if we see blue skies all day long, why is the sunset red? Above, we found that red is the least scattered by gas molecules. During sunset, the Sun approaches the horizon and the sunbeam is directed to the Earth's surface not vertically, as during the day, but at an angle.

Therefore, the path that it takes through the atmosphere is much longer than what it takes during the day when the Sun is high. Because of this, the blue-blue spectrum is absorbed in a thick layer of the atmosphere, not reaching the Earth. And longer light waves of the red-yellow spectrum reach the surface of the Earth, coloring the sky and clouds in the red and yellow colors characteristic of sunset.

Why are clouds white?

Let's touch on the topic of clouds. Why are there white clouds in the blue sky? First, let's remember how they are formed. Moist air, containing invisible steam, warms up near the surface of the earth, rises and expands due to the fact that the air pressure at the top is less. As it expands, the air cools. When a certain temperature is reached, water vapor condenses around atmospheric dust and other suspended solids, and as a result, tiny droplets of water are formed, the merger of which forms a cloud.

Despite their relatively small size, water particles are much larger than gas molecules. And if, meeting air molecules, the sun's rays are scattered, then when they meet water drops, the light is reflected from them. At the same time, the initially white sunbeam does not change its color and at the same time “paints” the cloud molecules white.

It would seem that at school every diligent and not very diligent student knows what colors the spectrum is decomposed into, what each of the colors represents. However, no matter how diligently a child studies, he will never be answered the main questions that have been troubling his restless mind since early childhood: why is the sky blue and why is the sunset red?

If you plunge a little into physics, you can find that the red spectrum has the worst scattering. That is why, in order for the lights of an object to be visible from afar, they are made red. And yet, why is the sunset red and not blue or green?

Let's try to think logically. When the sun is directly at the horizon, its rays have to overcome a much greater layer of the atmosphere than when the sun is at its zenith. Due to its low scattering, the red color passes through this layer of the atmosphere almost unhindered, and all other colors of the spectrum are scattered so strongly, passing through the thickness of the Earth's air space, that they are actually not visible at all. That's why the sunset is red!

From this we can conclude that the sunset will be the redder, the greater the layer of the atmosphere between the sun and our eye. Also, in order for the sunset to be redder, or even crimson, you just need to dust and pollute the air, then colors other than red will scatter even more.



Everyone knows that depending on the celestial point in which we observe the Sun, its color can vary greatly.

For example, at the zenith it is white, at sunset it is red, and sometimes even crimson. In fact, this is only an appearance - it is not the color of our luminary that changes, but its perception by the human eye. Why is this happening?

The solar spectrum is a combination of seven primary colors - remember the rainbow and the famous saying about the hunter and the pheasant, which determines the color sequence: red, yellow, green, and so on until purple.

But in an atmosphere filled with various types of aerosol suspensions (water vapor, dust particles), each color scatters differently. For example, violet and blue are best scattered, and red is worse. This phenomenon is called dispersion of sunlight.

The reason is that color, in fact, is an electromagnetic wave of a certain length. Accordingly, different waves have different wavelengths. And the eye perceives them depending on the thickness of the atmospheric air that separates it from the source of light, that is, the Sun.

Being at the zenith, it appears white, because the sun's rays fall on the Earth's surface at a right angle (naturally, that place on the surface where the observer is located is meant), and the thickness of the air that affects the refraction of light is relatively small. A white person seems to be a combination of all colors at once.

By the way, the sky appears blue also due to the dispersion of light: since blue, violet and blue colors, having the shortest wavelengths, scatter in the atmosphere much faster than the rest of the spectrum. That is, passing red, yellow and other rays with longer wavelengths, atmospheric particles of water and dust scatter blue rays in themselves, which give the sky its color.

The farther the Sun makes its usual daily path and descends to the horizon line, the greater the thickness of the atmospheric layer becomes, through which the sun's rays have to pass, and the more they scatter. Red is the most resistant to scattering because it has the longest wavelength. Therefore, only he is perceived by the eyes of an observer who looks at the setting star. The remaining colors of the solar spectrum are completely scattered and absorbed by the aerosol suspension in the atmosphere.

As a result, there is a direct dependence of the scattering of spectral rays on the thickness of atmospheric air and the density of the suspension it contains. Vivid evidence of this can be observed with global emissions into the atmosphere of substances denser than air, for example, volcanic dust.

So, after 1883, when the famous eruption of the Krakatau volcano took place, for quite a long time in the most diverse places on the planet one could see red sunsets of extraordinary brightness.