Why the sky is blue - A very difficult question with an uneasy answer. If you avoid a scientific language, then the sky is blue because red light is scattered the least than others, and purple is the greatest.
Many people know that white light consists of 7 primary colors: red, orange, yellow, blue, blue, green and purple. Each color can change as the wavelength decreases. So, for example, astronauts who are in orbit can see a rather white Sun on a black background. The fact is that astronauts see light without distortion in ordinary airless space, and we on Earth are looking at the Sun with the “filter” that our atmosphere creates.
Of all the 7 colors of the spectrum, red is the least scattered, a little more orange, yellow, etc. For this reason, at sunset and dawn, we see the sun orange-red. But when it rises higher and the layer of the atmosphere becomes thinner and thinner, the scattering of light will be less, which means that the Sun will become whiter and yellower.
Tie color and wavelength
What happens if we look at the sky, away from it? Then the red rays will pass to the side and practically will not dissipate. The orange rays will dissipate a little, the yellow ones more, and so on, until the violet light dissipates as much as possible. So we can see with you something in between a too strong violet light and a very weak red, in other words an atmosphere that will be clearly expressed by blue light.
- It is interesting -
This whole process is very complex and needs some scientific knowledge. The whole nature of this phenomenon was explained by the Englishman John William Strett, Lord Rayleigh III in 1899.
Why the sky is blue? - video
Why the sky is blue is very difficult to find the answer to such a simple question. Many scientists puzzled for an answer. The best solution to the problem was suggested about 100 years ago by the English physicist Lord John Rayleigh. But let's start over. The sun radiates a blindingly pure white light. So the color of the sky should be the same, but it is still blue. What happens to the white light in the earth's atmosphere?
White light is a mixture of colored rays. With the help of a prism we can make a rainbow. A prism splits a white ray into color bars: red, orange, yellow, green, blue, blue and violet. Connecting together, these rays again form white light. It can be assumed that sunlight first splits into colored components. Then something happens, and only the blue rays reach the surface of the Earth.
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. In the atmosphere there are still water vapor and ice crystals. Dust and other small particles are suspended in the air. In the upper atmosphere there is a layer of ozone. Maybe this is the reason? Some scientists believed that the ozone and water molecules absorb the red rays and let the blue light through. But it turned out that the atmosphere just does not have enough ozone and water to paint the sky blue.
In 1869, Englishman John Tyndall suggested that dust and other particles scatter light. Blue light is scattered to the least extent and passes through layers of such particles, reaching the surface of the Earth. In his laboratory, he created a model of smog and lit it with a bright white beam. The smog has turned deep blue. Tyndall decided that if the air were absolutely clear, then nothing would diffuse 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, and not dust or smoke, that colors the sky blue.
The explanation is why the sky is blue. Part of the sun's rays passes between the gas molecules, without colliding with them, and without changes reaches the Earth's surface. The other, most of it, is absorbed by gas molecules. When photons are absorbed, the molecules are excited, that is, charged with energy, and then emit it in the form of photons again. These secondary photons have different wavelengths and can be of any color - from red to violet. They fly away in all directions: to the Earth, and to the Sun, and to the sides. Lord Rayleigh suggested that the color of the emitted beam depends on the prevalence in the beam of quanta of a particular color. When a gas molecule collides with the photons of the sun's rays, there are eight blue quanta per one secondary red quantum.
What is the result? Intense blue light literally pours on us from all sides of the billions of molecules of atmospheric gases. Photons of other colors are mixed with this light, so it does not have a pure blue tone.
It turns out very few people know the answer to this seemingly "always hanging question in the air." Often children ask about it, but adults are not ready to give an explanation. Many believe that this question is from a series of those that we cannot answer at all, such as "where is the end of the universe." There are people who believe that this is the color of a mixture of nitrogen and oxygen, when there is a lot of these gases and they are highlighted by the sun. There are those who associate the color of the sky with the refraction of light in the layers of the atmosphere. Those who were excellent pupils at school will say that, they say, the air disperses the blue color more intensively than all the other colors of the spectrum according to Rayleigh's law, often without understanding the essence of this scattering. By the way, the question of the color of the sky was decided by physicists only in the twentieth century. Therefore, we should not be particularly ashamed.
And although this issue is not directly related to temperature, let's try to figure it out. We will not dig very deep into physics, but we will remind you the main points about light and air.
Sunlight is a mixture of radiations of all colors of the rainbow, i.e. electromagnetic waves with frequencies of oscillations such that can affect the retina of the human eye. Violet color corresponds to the wavelength of 380 nm, red - 720 nm. In the retina there are cones responsible for color perception. There are three types of cones: blue (responsible for the high frequency range), green (responsible for mids) and red (for low frequencies). The sensitivity ranges of cones overlap, but the maximum falls on a certain color.
Air molecules in a normal state have no charge, they are neutral. However, they consist of charged particles - electrons and nuclei. Under the influence of the electric field, the nuclei are shifted in one direction, the electrons - in the other, and a dipole with its own electromagnetic field is obtained. If a dipole falls into an alternating electromagnetic field, then it begins to oscillate, that is, the positive and negative charges are shifted back and forth and the dipole itself begins to radiate an electromagnetic wave. In our case, the electromagnetic wave of sunlight causes air molecules to turn into dipoles radiating electromagnetic waves. Moreover, the direction of the study of dipoles can be all sorts of. By the law of conservation of energy, the light wave loses its intensity in the original direction. This is the main mechanism of light scattering in the air. Rather, it’s not even about scattering, but about the emission of air molecules by the action of light. We look through the atmosphere and actually see the light from the sun and the light emitted by the molecules of our atmosphere. Why is he not white, but blue?
The fact is that the radiation intensity of the dipole is proportional to the fourth power of the radiation frequency. The most intensively emitted by dipoles of the wave with the maximum frequency and energy, corresponding to blue light. Waves of red light interact less with air molecules. Those. when passing through the atmosphere, there is a sort of filtering of white color across the spectrum. Air molecules emit mainly blue color, that is, light that excites blue and green retinal cones is much stronger than red cones.
John Tindal was the first to take a step towards the correct explanation of the color of the sky in 1865. He discovered that when rays of light pass through an environment in which small particles of impurities are suspended, the blue color dissipates more intensively than red. As a result, we see the coloring of the transmitted light in blue. This can be observed if you look at the side of the beam of light passing through the water, slightly fogged with milk. If you look not from the side, but in the direction of the beam, then the light becomes reddish, because the blue component dissipated.
A few years later, the British scientist Lord Rayleigh studied this effect in more detail. He showed that the intensity of light scattering on particles of very small sizes is inversely proportional to the fourth power of the radiation wavelength. From this it followed that blue light is scattered 10 times more intensely than red.
Tyndall and Rayleigh thought that the blue of the sky was due to the presence of small particles of dust and water vapor in the atmosphere. Later, scientists realized that if this were true, we would observe significantly more variations in the color of the sky with changes in humidity, nebula and air pollution than we are seeing now. The problem was solved by Einstein, who in 1911 derived a formula describing the scattering of light by molecules. The formula confirmed all previous experiments. It was proved that it is not dust and steam, but air molecules that scatter light, because (as mentioned above) the electromagnetic field of light initiates electrical dipole moments in molecules.
Why is the sky not purple, but blue? After all, purple waves are shorter than blue ones. The first reason is that the spectrum of solar radiation is not uniform. Violet color there is less. In addition, the violet rays are scattered in the uppermost layers of the atmosphere. The second reason - the sensitivity of our cones to purple is lower than to blue. The third reason is that the blue color irritates not only the blue cones in the retina, but also a little red and green. Therefore, the color of the sky is not pale, but saturated blue, especially when the air is clear.
The color of the sunset is explained by the scattering of light on air molecules. Having traveled a long way from the Sun to the Earth, the ray loses all blue shades. Only yellow and red tones reach the eye. Around the sea, the sunset can even be orange, thanks to particles of salt in the air, which are responsible for the dispersion of Tyndall.
Note that the composition of the atmosphere, i.e. the presence of nitrogen and oxygen, the color of the sky is almost independent. If a planet has a transparent atmosphere of sufficient thickness and density, illuminated by a luminary, whose spectrum is white, like that of the Sun, then the sky will be blue there.
How, then, to explain that images from spacecraft landing on Mars indicate that the sky is pink and red? This is because the atmosphere of Mars is very thin and polluted by dust. The scattering of sunlight occurs not on molecules, but mainly on suspended dust impurities. Many dust particles are larger than the wavelengths of light and consist of iron oxide, which is red in color.
Now you know that answering the question “why the sky is blue” is not very simple. We understand something, but what to say to the children? Probably, our beautiful atmosphere consists of air that glows with blue light when the Sun warms it. Because blue is the strongest of all the colors of the rainbow.
“Why is the sky blue?” Or “Why is the sky blue” is a fairly common question, but many will find it difficult to answer.
I will try to open the topic and fully answer the question. To answer with minimal (zero!) Use of formulas, or else they say each formula in the text reduces its audience by 50%, which I would not like.
Absolutely avoiding physics will not work, but I will rely on the fact that you are at a distance from a school course, but remember, or you are simply interested.
So, in fact, the answer to this question sounds very briefly - Rayleigh scattering.
Those who know what Rayleigh dispersion is, in principle, may not read further, for them the explanations will be trivial. Those who do not remember or never knew about it - you are welcome.
In this question, we have three reference points, three factors that can affect (and influence) how we see the sky.
The first is the Sun. 99% of the light around us, day and night, radiates it. During the day it shines by itself, at night its light reflects the moon. In the cities, in the evenings, of course, it is also light, but this is a drop in the ocean compared to what our star "gives out" to us. I generally keep quiet about the light of other stars, they are eclipsed even by an ordinary hand flashlight. Almost everything that we see, we see thanks to him is foolish to deny his involvement in our question.
The usual image of the sun. Dark spot - Venus passing through the solar disk, 2012. By the way, what color is the sun? Ask anyone, child, adult and the Sun will immediately answer you - well, well, except that the astronomer will answer correctly, and even that may be wrong. After all, the Sun, a star of the “yellow dwarf” class.
So the Sun is not yellow, but white! Yes, yes it is white. Despite the fact that it seems, despite the fact that it is painted everywhere with yellow and even in astronomical photographs it is almost always yellow, NASA technicians often “paint” the Sun in the usual yellow or orange color - but the sun is white.
And this is how the Sun actually looks like, if you lower the intensity of the light “to remove the brightness“ The fact that the Sun is white is very important, it is for this reason that we are seeing the colors, not the monochrome image. The physical definition of white light is somewhat different from the biological concept, but in our case it is enough to understand that the sun shines with all the colors of the rainbow "the same" (or almost the same), and a mixture of all colors gives us white. (for those who want to penetrate more deeply -)
The schematic distribution of the “colors” emitted by the Sun, all colors visible in the rainbow are present, and by the way there is very little yellow. The peak of intensity falls on purple, blue and green. The “wave” of distribution is shifted towards the purple end. The light radiated by the Sun flies to our Earth for about 8 minutes (8.29 minutes). It passes through the earth's atmosphere, and this is exactly what we call the sky and it is second point - Earthly atmosphere.
It is in the atmosphere of the Earth and all the magic happens.
Sunlight passing through the atmosphere is refracted, scattered, absorbed and reflected - i.e. behaves as it should be.
We are interested in dispersion because it paints the sky in blue.
For example, take the surface of the water. Everyone knows that if we look at the coin at the bottom of the fountain and try to get it, we will have a “surprise”. We miss, and the hand immersed in water, as if it breaks. This is called refraction. Refraction of light on the border of different environments - water and air.
Besides the fact that they are different substances (air and water), they are also different in density. It is this fact that interests us.
In the atmosphere of the Earth there are so-called density fluctuations - inhomogeneities in density. And very small, at the molecular level. I mean the uneven distribution (density) of gas molecules that make up the atmosphere. At the “boundary” of these fluctuations, the light is “refracted”.
The atmosphere is big compared to the molecules - it is amazingly huge. So it is easy to understand - there are a huge amount of such heterogeneity in it. The beam of light is refracted at each fluctuation and slightly changes its direction. On each heterogeneity in a random direction. (for comparison, imagine a downtrodden shower from which gushes in all directions) The combination of multidirectional refractions and gives us scattering.
The scattering effect we need to explain is called Rayleigh scattering. Honestly, the name and how it differs from others is not the essence, it is only necessary to designate a general principle.
The principle of Rayleigh scattering says the following: the shorter the wave of light, i.e. the color of light is closer to blue and violet, the greater the scattering intensity, respectively, the longer the wave, the closer to red, the smaller the scattering intensity.
For blue and red light, the ratio of the intensity of scattering, based on the formulas that I promised not to give, is about 4.5 times. Blue dissipates “better and more” than red 4.5 times.
By the way, although there is still purple in front of blue in the rainbow and it actually scatters even better than blue, the sky is still blue, not purple. Why the sky is not purple, I will tell a little lower.
The atmosphere plays the role of a peculiar blue lamp shade, and the Sun has a light bulb in it. If you look at the lamp with a blue lampshade so that the light does not shine into your eyes, you will see a steady blue light emanating from the entire lampshade, but if you look directly at the light bulb, the lampshade distortion will almost disappear and you will see the light (color) of the light bulb practically unchanged. So is our sky. We see repeatedly scattered blue light. The remaining colors are less dispersed. The sky does not glow with them, and they directly fall into the eye of the observer.
Most of the day, the Sun is not at its zenith (in fact, it is there once a day, and then at the equator), and it’s understandable that you shouldn’t look directly at the Sun, so we walk all day under the even blue light of our celestial lampshade .
It also explains why the sky is “bluer” at the edges, closer to the horizons, and the closer to the Sun, the whiter it is. Along the edges there is more air and the amount of diffused light there is higher.
The black dotted arrow shows how the color of the sky (near the horizon) changes over the course of the day to sunset.More bluer, less bluer is nice, but it’s written in the heading, and we see the blue sky rather than the blue sky every day. Here we come to the third factor is our eyes and to such a concept as the perception of an integral, total, picture.
How and why this way our eyes are arranged is a separate topic, very extensive and interesting. Now just enough to give a few facts. Our eyes perceive three colors best: red, green and blue. This color model is called RGB - an abbreviation of the English words Red, Green, Blue, i.e. red, green, blue.
And red is perceived much better than green, and green is much better than blue.
For example, to purple, our eyes are generally insensitive. There are not so many purple things around us. The only thing that immediately comes to mind is eggplant. Yes, and it is easier to call eggplant gray-green or even brownish-yellow, and some of them are generally called “blue ones” rather than purple.
So it turns out that the overall picture is perceived by our eyes rather as blue, and not purple. And as I said above, purple dissipates even better than blue, and most of it simply does not get in the eye of the observer.
Pay attention to the color mixing illustration. The dotted arrow marks the approximate change in the color of the sky.
Say at noon it is bluish, towards evening (or closer to the Sun) begins to turn blue. 2-3 hours before dusk becomes light, almost white.
The sun rolls toward sunset and the sky turns yellow, blushes and fades away into red. The closer to sunset, the more air there is between the observer and the sun. The blue light is almost all scattered and does not reach the observer.
Red prevails, its dispersion is lower and, as a consequence, penetrating power is higher, it overcomes the atmosphere more easily.
That's basically the whole tale of the “Blue Sky”.
It remains, perhaps, to rehabilitate a little green. Yes, green sky does not happen, well, at least a pronounced green. At any given time, until it gets dark, we still see 3 colors, they always blend in our eyes. It turns out that at the moment when green dominates, blue and red are also quite strong - we get the middle of the dotted line - the sky is whitish, with shades of yellow or blue. And the rest of the time it is dominated by blue or red.
But green can be seen. This very rare phenomenon available far from everywhere is called - “Green Ray”.
Although the Green Ray is an extremely rare phenomenon, it is much easier to explain it.
The ancient Greeks believed: "The sky is blue because it is created from the purest rock crystal!" In this case, the crystal is multi-layered - and therefore has in blue. If you put a piece of ordinary glass in front of you, it will be transparent. However, if you pile up a few pieces and try to look through them, it turns out that you will see not something that is actually behind the whole structure, but some kind of incomprehensible blue.
So in our case, the sky is a series of crystal spheres, which are located with jeweler accuracy one inside the other. In the middle of this set of spheres, the Earth is located with its fortresses, taverns, roads, mountain peaks, temples, cities and seas. On one sphere is the brightly blazing Sun. On another sphere is the moon. The third sphere is covered with an infinite set of stars, which continually break away from the crystal surface and fall down. All other spheres are placed on one of a large number of planets.
All these spheres rotate, and each has its own direction and speed. They rotate without rattle and squeak, and in the very center of this amazing system our planet is like no other and important planet located in the “world” emptiness. Probably a majestic sight!
In this theory, why the sky bluesincerely believed by the ancient Greeks. However, what exactly made them think so? After all, the sky is impossible to touch, it can only be contemplated. Contemplate and reflect, build the most incredible guesses. In our time, such conjectures are usually called “scientific theory,” one ancient Greeks did not bother, and so they called them - conjectures.
Why is the sky blue (according to scientists)?
Modern scientists were able to find the right answer and prove why the sky is blue. Physics for quite a long time hid this secret, or rather the atmosphere of our planet. As everyone knows, the air itself is a colorless gas, however, when the sun's rays penetrate into it, the light begins to disintegrate into 7 primary colors:
Since in this process, blue and blue have a clear advantage - because we see the sky blue-blue.
The most successful example of this process is the comparison of day and night. At night, the sun's rays are absent, because the sun at the moment will illuminate the opposite side of the planet. Due to the absence of light, we can see the true color of the atmosphere, to be precise, the absence of any color, transparency. Through the transparent air we have the opportunity to see other galaxies, stars, boards, black space. At that moment, when the Sun begins to illuminate our side of the planet again - the sky becomes azure. Thus, the sky is a kind of blue curtain, behind which the cosmos hides from us in the daytime. That is why the sky is blue during the day, and transparent at night, which is why it seems to us that it is black.
Why is the color of the sky blue, but the sunsets are scarlet? The thing is that red light has the longest wavelength. Due to this, the red color can make its way through the thickness of the earth's atmosphere even when the sunlight has completely disappeared beyond the horizon line.