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.

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 do not even think about why the sky changes color with the change of time of day.


We are accustomed to bright blue on a fine sunny day and to the fact that in autumn the sky becomes hazy gray, losing its bright colors. But if you ask a modern person why this happens, then 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 a school course in physics, we should know that differences in the color perception of objects depend on the wavelength of light. Our eye can only distinguish a fairly narrow range of wave radiation, with blue being the shortest and red being the longest. Between these two primary colors lies our entire palette of color perception, expressed by wave radiation in different ranges.

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


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

Therefore, a stop signal or any other 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 the 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 the rays of almost the entire visible range, except for the red ones, which are the longest and therefore most resistant to interference. All other light waves are either scattered or absorbed by water vapor and dust particles present in the atmosphere.

The lower the sun drops in relation to the horizon, the thicker the layer of the atmosphere the light rays have to overcome. Therefore, their color is increasingly shifted towards the red part of the spectrum. A folk sign is associated with this phenomenon, saying that a red sunset portends a strong wind the next day.


The wind originates in the high layers of the atmosphere and at a great distance from the observer. Oblique solar rays highlight the outlined 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 the length of light waves also explain the pure blue of the daytime sky. When the sun's rays fall directly on the surface of the earth, the layer of the atmosphere they overcome has the smallest thickness.

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

The fact is that the cells of the human eye, which are responsible for color perception, perceive blue much better than purple. Yet purple is too close to the edge of the perceptual range.

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

Gray sky of bad weather

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


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

> > Why is the sky blue

It will be interesting for children to know why is the sky blue with photo: Earth's atmosphere, the influence of composition, the movement of light along a wave, reflection, absorption and scattering.

Let's talk about why the sky is blue in a language accessible to children. This information will be useful to children and their parents.

When children look at the sky, they see an endless blue. Many even spend all day on the grass watching the clouds and the color of the sky. It's time explain to children Why is the sky still blue?

To give complete explanation for children, parents should consider the reasons that may lead to such a phenomenon. But it can be difficult. At school you have heard about the existence of an atmosphere. It is a mixture of molecules (various gases) surrounding the planet. Depending on the location of your country and city, there may be more water in the atmosphere (near the ocean) or dust (if there is a volcano or desert nearby).

Farther for the little ones necessary explain concept of light waves. Light is energy transmitted in waves. Each type defines its own wave, oscillating in magnetic and energy fields. Light is divided into very many types, which can have a longer (or shorter) length. Children must remember that light is included in a large group - "electromagnetic fields". The visible (which we observe with our own eyes) is part of it. It consists of a whole stream of colors, namely the entire spectrum of the rainbow: red, orange, yellow, green, blue, indigo and violet.

Light travels in a straight line, which is called the "speed of light." He travels until he encounters an obstacle in the form of a speck of dust or a drop of water. Then everything depends on the size of the wavelength and the object. Dust and water are longer than the wavelength, so the light bounces off - "reflection". It spreads in different directions, but remains white because it continues to contain the entire rainbow spectrum. But gas molecules are smaller. Therefore, it is necessary explain to children that this collision leads to different results.

In this case, the light is not reflected but absorbed by the molecule. Then it fills up and begins to radiate part of the color. Although now it still contains the entire spectrum, it highlights a specific one. High frequency (blue) is absorbed faster than low frequency (red). This scientific process was discovered and described in the 1870s by the English physicist Lord John Rayleigh. That is why the phenomenon was called "Rayleigh scattering".

This is the reason why we admire the blue sky. When light travels through the air, the red or yellow part is not involved. But blue is absorbed and reflected. This is especially noticeable when looking at the horizon from a distance. The blue color then appears lighter. Now you know what color the sky is and how it appears.

Surely every person at least once thought about why the sky is blue, and not green or, for example, orange. It seems like such a simple question! But how to find the answer to it? How to explain to children why the sky is blue? Let's figure it out! After all, physicists have long offered us several versions. Remarkably, scientific disputes on this topic are still ongoing. So each of us can interpret the answer in our own way.

Why is the sky blue - most popular answers

So why is the sky blue, or at least appears to be? To give the correct answer to this seemingly simple question for children, you need to immerse yourself in the world of physics. Then this phenomenon will be quite understandable. After all, even at school, in the lessons of natural history, students were told about why we see the sky blue. The whole point is that in this way sunlight and the ozone layer interact with each other. However, not everything is as clear-cut as it seems at first glance. There are several theories explaining the mechanism of this interaction. Let's get to know them!

Theory #1

The most simple and understandable theory that allows you to explain why the sky is blue, and helps to give an answer to children, concerns a very simple phenomenon. The point is that air scatters light in different spectra. The result is a blue glow, and a short light wave makes this scattering more intense.

On a note! By the way, it is this fact that can explain the fact that at sunset the color of the sky becomes different. Just the angle of incidence of the sun's rays changes.

Speaking in simple words and giving a short answer, then the main reason for the blueness of the sky is dispersion, that is, the decomposition of light into spectra. The higher the sun is above the horizon, the bluer the sky appears.

Theory #2

Another theory that explains why the sky is blue is that this phenomenon is due to the dispersion of various particles in the atmosphere. Here we are talking about mechanical dust, ordinary steam, plant pollen, and other small inclusions. All together they work as a dispersion medium. Due to this interaction, our eye picks up only a bluish color.

Note! This theory has been rejected by many scientists. The problem is that it does not explain the change in the color of the sky in winter or in the northern regions.

Theory #3

If you don’t know how to explain to a three-year-old child why the sky is blue, then get acquainted with this theory. Some scientists conducted a study and concluded that the light flux is white, that is, it is the sum of all spectra that can be decomposed into other colors (rainbow). It passes through the atmosphere, which consists of a variety of particles. When a sunbeam passes through the atmosphere, the particles become active and release their own (i.e. additional) rays. As a result, the light of the sun turns blue. There is a kind of natural luminescence.

At the moment, it is the third theory that most scientists consider to be the most correct. It gives the most comprehensive answer to the question of why the sky seems blue to us. It reveals most of the factors. So far, no discrepancies or inconsistencies have been identified. Although there are a number of researchers who claim that this option is not true.

There are millions of questions that, being children, we do not receive an answer, and when we grow up, we are simply embarrassed to ask. One of these unanswered questions: "why is the sky blue?" And everything would be fine, and you can live without this knowledge, but when a child begins to ask such tricky questions to his parents, they often become ashamed, and they begin to change the subject. Then the child grows up not knowing the answer, he has his own children and everything repeats again. Let's break this "vicious circle" and understand the reasons why the sky is blue. Consider the issue from all possible points of view.

The phenomenon of blue sky in terms of physics

Let's get straight to the point, the sky is blue because the earth's atmosphere scatters the light of the sun. All research conducted over the past 200-300 years comes down to this. Consider a few axioms that affect the blue sky phenomenon:

1. The white light of the sun is a combination of different color streams. White color "separately" does not exist. As everyone knows, there are only 7 colors (red, orange, yellow, green, blue, blue, purple), the rest of the colors are obtained only when they are combined. White color is obtained by combining all seven colors. It is worth considering that it is precisely the colors that we can distinguish with the eye that are meant.
2. The atmosphere is not empty, it consists of many gases: nitrogen (78%), oxygen (21%), carbon dioxide, water in its various states (steam, ice crystals). There is also a lot of dust around us, elements of various metals. All of them distort the white light of the sun.
3. The air that surrounds us and that we breathe is actually opaque. In any case, in large quantities. We do not live in a vacuum, after all.

From these three facts we will proceed further.

Story

Back in the 19th century, a scientist named John Tyndall conducted research that proved that we see the sky blue because of particles in the atmosphere. In his laboratory, he artificially created a fog with dust particles and directed a bright white beam at it - the color of the fog changed to bluish. 30 years later, in 1899, the physicist Rayleigh refuted the research of his predecessor and published evidence that the sky is blue because of air molecules and no dust in it. This phenomenon is called diffuse sky radiation You can read more about this on Wikipedia.

The sky looks blue because air scatters short wavelength light more than long wavelength light. Since blue light has a shorter wavelength, at the end of the visible spectrum, it scatters more in the atmosphere than red. (Source: Wikipedia)

What is light? Light is a stream of photons, some we can see with our eyes and some we can't. So, for example, we see the standard spectrum of colors, but the ultraviolet, which also emits the sun, does not. What color we see in the end depends on the "wavelength" of this stream. This wavelength determines what color you get.

So. We have determined that the sun sends us quanta with a wavelength that corresponds to white, but how does it turn into blue as it passes through the atmosphere? Let's take the example of a rainbow. Rainbow - is a direct example of the refraction of light and its division into a spectrum. You can create your own rainbow using a glass prism at home. The decomposition of color into a spectrum is called dispersion.

So, our sky functions as a prism. Most white light changes its wavelength as it passes through gas molecules in the atmosphere. As a result, photons “leaving” the molecules have a different color. This color can be either purple, red, or blue and blue.

Why do we see blue and not red?

What color we eventually see when light travels from the sun to the earth depends on which photons prevail. For example, when light passes through the atmosphere, the number of blue color quanta is 8 times more than red, and violet is 16 times! This is due to the very different wavelength, so violet and blue scatter strongly, and red and yellow scatter much worse. Based on this theory, the sky should be purple, but it is not. This is due to the fact that purple is much worse perceived by the human eye, unlike blue. That is why the sky is blue.

Video about why the sky is blue:

Why is the sky blue during the day and the sunset is red

Everything, again, is connected with the dispersion of color. The angle of incidence of solar white light becomes smaller, and the light passes through more air molecules, the wavelength of light increases. This amount is enough to diffuse to red.

The answer to the question why the sky is blue for children

If a child asked you a question about the blue sky, you certainly will not tell him about dispersion, spectra and photons. It is enough to quote from the children's book "100 Children's Why" Tatiana Yatsenko:

Usually we draw the sun's rays in yellow. But in fact, the light of the sun is white and consists of seven colors. These are the colors of the rainbow: red, orange, yellow, green, blue, indigo, violet. Not all colors pass through the air, only blue, indigo and violet. They color the sky.

This will be enough. On our website, you can also download a presentation on the topic: “Why the sky is blue” at the link: It may come in handy in the classroom at school.