Why do we see blue skies. Why is the sky blue and the sunset red? What is atmosphere
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 is known that the sky is blue- this is the reason for the interaction of the ozone layer and sunlight. But what exactly is happening in terms of physics and why is the sky blue? There were several theories about this. All of them, in the end, confirm that the main reason is the atmosphere. But the mechanism of interaction is also explained.
The main fact concerns sunlight. Sunlight is known to be white. White is the sum of all spectra. It can be decomposed into rainbows (or spectra) as it passes through a dispersion medium.
Based on this fact, scientists have proposed several theories.
First theory attributed the blue color to scattering by particles in the atmosphere. It was assumed that a large amount of mechanical dust, particles of plant pollen, water vapor and other small inclusions work as a dispersion medium. As a result, only the bluish color spectrum reaches us. But how then to explain that the color of the sky does not change in winter or in the north, where there are fewer such particles or their nature is different? The theory was quickly rejected.
Next theory assumed that the light flux of white color passes through the atmosphere, which consists of particles. When a light beam passes through their field, the particles are excited. Activated particles begin to emit additional rays. This is what turns the sun into a bluish color. White light, in addition to mechanical scattering and its dispersion, also activates atmospheric particles. The phenomenon resembles luminescence. For now, this explanation is .
The latest theory the simplest and it is sufficient to explain the main cause of the phenomenon. Its meaning is very similar to previous theories. Air is able to scatter light across the spectra. This is the main reason for the blue glow. Short wavelength light scatters more intensely than short wavelength light. Those. violet diffuses more strongly than red. This fact explains the change in the color of the sky at sunset. It is enough to change the angle of the sun. This is what happens when the earth rotates, and the color of the sky changes to orange-pink at sunset. The higher the sun is above the horizon, the more blue light we will see. The reason for everything is the same dispersion or the phenomenon of decomposition of light into spectra.
In addition to all this, you need to understand that it is impossible to exclude all the factors indicated above. After all, each of them gives some contribution to the overall picture. For example, several years ago in Moscow, as a result of abundant flowering of plants in the spring, a dense cloud of pollen formed. It turned the sky green. This is a rather rare phenomenon, but it shows that the rejected theory about microparticles in the air is also the place to be. However, this theory is not exhaustive.
When the wind throws a white fluffy transparent cape over the beautiful blue sky, people begin to look up more and more often. If at the same time it also puts on a large gray fur coat with silver threads of rain, then those around hide from it under umbrellas. If the outfit is dark purple, then everyone is sitting at home and wanting to see the sunny blue sky.
And only when such a long-awaited sunny blue sky appears, which puts on a dazzling blue dress, decorated with golden sunbeams, people rejoice - and smiling, leave their homes in anticipation of good weather.
The question of why the sky is blue has puzzled people's minds since time immemorial. Greek legends have found their answer. They claimed that this shade is given to it by the purest rock crystal.
At the time of Leonardo da Vinci and Goethe, they were also looking for an answer to the question why the sky is blue. They believed that the blue color of the sky is obtained by mixing light with darkness. But later this theory was refuted as untenable, since it turned out that by combining these colors, you can get only the tones of the gray spectrum, but not the color one.
After some time, the answer to the question of why the sky is blue was tried to be explained in the 18th century by Mariotte, Bouguer and Euler. They believed that this was the natural color of the particles that make up the air. This theory was popular even at the beginning of the next century, especially when it was found that liquid oxygen is blue, and liquid ozone is blue.
The first more or less sensible idea was given by Saussure, who suggested that if the air were completely clean, without impurities, the sky would turn out to be black. But since the atmosphere contains various elements (for example, steam or water drops), they, by reflecting color, give the sky the desired shade.
After that, scientists began to get closer and closer to the truth. Arago discovered polarization, one of the characteristics of scattered light that bounces off the sky. In this discovery, the scientist was definitely helped by physics. Later, other researchers began to look for the answer. At the same time, the question of why the sky is blue was so interesting for scientists that a huge number of different experiments were carried out to clarify it, which led to the idea that the main reason for the appearance of the blue color is that the rays of our Sun simply scatter in the atmosphere.
Explanation
Rayleigh, a British researcher, was the first to create a mathematically sound answer to molecular light scattering. He suggested that light is scattered not because of the impurities that the atmosphere possesses, but because of the air molecules themselves. His theory was developed - and here are the conclusions scientists came to.
The sun's rays make their way to the Earth through its atmosphere (a thick layer of air), the so-called air shell of the planet. The dark sky is completely filled with air, which, despite being completely transparent, is not a void, but consists of gas molecules - nitrogen (78%) and oxygen (21%), as well as water droplets, steam, ice crystals and small pieces of solid material (for example, particles of dust, soot, ash, ocean salt, etc.).
Some rays manage to freely pass between gas molecules, completely bypassing them, and therefore reach the surface of our planet without changes, but most of the rays collide with gas molecules that come into an excited state, receive energy and release multi-colored rays in different directions, completely coloring the sky, resulting in a sunny blue sky.
White light itself consists of all the colors of the rainbow, which can often be seen when it is broken down into its component parts. It so happens that blue and violet colors scatter the most because they are the shortest part of the spectrum, since they have the shortest wavelength.
When mixed in an atmosphere of blue and purple with a small amount of red, yellow and green, the sky begins to "glow" blue.
Since the atmosphere of our planet is not homogeneous, but quite different (it is denser near the Earth's surface than at the top), it has a different structure and properties, we can observe blue overflows. Before sunset or sunrise, when the length of the sun's rays increases significantly, blue and purple colors are scattered in the atmosphere and absolutely do not reach the surface of our planet. The yellow-red waves successfully reach, which we observe in the sky during this period of time.
At night, when the sun's rays, falling on a certain side of the planet, have no opportunity, the atmosphere there becomes transparent, and we see the "black" space. This is how astronauts above the atmosphere see it. It is worth noting that the astronauts were lucky, because when they are over 15 km above the earth's surface, during the day they can simultaneously observe the Sun and stars.
Sky color on other planets
Since the color of the sky is largely dependent on the atmosphere, it is not surprising that on different planets it is of different colors. Interestingly, the atmosphere of Saturn is the same color as on our planet.
Very beautiful aquamarine skies of Uranus. Its atmosphere consists mainly of helium and hydrogen. It also contains methane, which completely absorbs red and scatters green and blue. The blue skies of Neptune: in the atmosphere of this planet there is not as much helium and hydrogen as ours, but there is a lot of methane, which neutralizes the red light.
The atmosphere on the Moon, a satellite of the Earth, as well as on Mercury and Pluto, is completely absent, therefore, light rays are not reflected, so the sky is black here, and the stars are easily distinguishable. The blue and green colors of the sun's rays are completely absorbed by the atmosphere of Venus, and when the Sun is near the horizon, the skies here are yellow.
On a clear sunny day, the sky above us has a bright blue color. In the evening, at sunset, the sky takes on a deep red color with numerous shades that is pleasing to the eye. So why is the sky blue during the day? What makes a sunset red? How does transparent air shimmer with blue and red hues at different times of the day?
I will present 2 answers here: the first one is more simplified for the general reader, the second one is more scientific and accurate. Choose for yourself which one you like.
1. Why is the sky blue and not green? Answer for dummies
Light from the sun or a lamp looks white, but white is actually a mixture of all 7 existing colors: red, orange, yellow, green, cyan, indigo, and violet (Figure 1). The sky (atmosphere) is filled with air. Air is a mixture of tiny gas molecules and small pieces of solid material such as dust. As sunlight travels through air, it collides with air particles. When a beam of light hits gas molecules, it can "bounce" in the other direction (scatter).
Some component colors of white light, such as red and orange, pass directly from the Sun into our eyes without scattering. But most blue rays "bounce" off air particles in all directions. Thus, the whole sky is literally pierced with blue rays. When you look up, some of this blue light reaches your eye and you see blue light from all over your head! Here, in fact, why the sky is blue!
Naturally, everything is simplified to the maximum, but below is a paragraph where the property of our beloved sky above our heads is more fundamentally described and the reasons that explain why the color of the sky is blue and not green after all!
2. Why is the sky blue? advanced answer
Let's take a closer look at the nature of light and color. Color, as everyone knows, is a property of light that our eyes and brain can perceive and define. Light from the sun is a large amount of white rays, which consist of all 7 colors of the rainbow. Light has the property of dispersion (Fig. 1). Everything is illuminated by the Sun, but some objects reflect rays of only one color, for example, blue, while other objects only reflect rays of yellow, etc. This is how a person defines colors. So, the Sun shines on the Earth with its white rays, but the atmosphere (a thick layer of air) envelops it, and when this white (consisting of all colors) ray passes through the atmosphere, it is the air that scatters (spreads) all 7 colored rays of the white sun ray, but with greater force, it is its blue-blue rays (in other words, the atmosphere literally begins to glow blue). Other colors directly fall from the Sun into our eyes (Fig. 2).
Why is blue the color most diffused in the atmosphere? This is a natural phenomenon, and it is described by Rayleigh's physical law. To put it more simply, there is a formula that Rayleigh deduced in 1871, and which determines how the scattering of light (a beam) depends on the color of this beam (that is, on such a property of the beam as its wavelength). And it just so happened that the sky-blue color has the shortest wavelength and, accordingly, the greatest scattering.
Why is the sky red during sunrise and sunset? At sunset or sunrise, the sun is low on the horizon, which causes the sun's rays to fall obliquely
yut to Earth. The beam length, of course, increases many times (Fig. 3), and therefore, at such a huge distance, almost the entire short-wavelength (blue-blue) part of the spectrum is scattered in the atmosphere and does not reach the Earth's surface. Only long waves, yellow-red, reach us. This is exactly the color the sky takes on during sunrise and sunset. That is why the sky, in addition to blue and blue, is also yellow and red!
And now, for a complete understanding of all of the above, a few words about what the atmosphere is like.
What is the atmosphere (vault of heaven)?
The atmosphere is a mixture of gas molecules and other materials that surround the Earth. Basically, the atmosphere consists of nitrogen gases (78%) and oxygen (21%). Gases and water (in the form of vapours, droplets and ice crystals) are the most common constituents of the atmosphere. There are also small amounts of other gases, as well as many fine particulate matter such as dust, soot, ash, salt from the oceans, etc. The composition of the atmosphere changes depending on the geographical location, the weather and much more. Somewhere there may be more water in the air after a rainstorm or near the ocean, somewhere volcanoes erupt large amounts of dust particles high into the atmosphere.
The atmosphere is denser in its lower part, near the Earth. It gradually thins out with height. There is no sharp gap between atmosphere and space. That is why we see overflows of blue and blue in the sky, precisely because the atmosphere in the sky is different everywhere, has a different structure and properties.
We welcome the most inquisitive on the pages of our site! Today we will touch on a question that often worries inquisitive minds (especially children's), but not everyone finds an opportunity to figure out why is the sky blue because the air is actually transparent. Let's try to answer it briefly.
What does Wikipedia say?
If we don’t know something, then we can always find the answer in Wikipedia. So let's take a look there and see what this resource tells us.
As a matter of fact, here is a link to the relevant material.
Well said on Wikipedia! True, somehow it is not very clear. The only thing that can be sorted out is the fact that the sun's rays reach our atmosphere, something happens to them, and we see a blue sky. No, this will not work, let's try to understand in more detail and in a more understandable language why the sky is blue.
In fact, the reason for everything is such a thing as " light scattering»!
Light scattering
So, the Sun emits rays that are white. White, as you know, includes all the colors of the spectrum visible to us. Evidence of that - rainbow. It arises for the reason that sunlight, falling into water droplets, is refracted and breaks up into different colors. We also observe blue skies for a similar reason.
This is how a rainbow is formed You may be interested in:
The fact is that there are many gas molecules in the air, which scatter sunlight. Light particles scatter in different directions, so the blue color of the sky is visible to both earthlings and astronauts from the ISS in the form of a blue halo. But why is it blue, because there are at least seven colors in the spectrum, as they say: "Every hunter wants to know where the pheasant is sitting!".
Interesting fact! A person inhales about 20 kg of air per day. We get this volume by taking 22,000 breaths a day.
Why is the sky blue?
Each color has its own wavelength. In the following figure, you can see how this indicator varies.
Violet diffuses too much, and the colors from green to red, on the contrary, do not scatter very intensively. So it turns out, blue and blue particles are the golden mean. Violet, despite the fact that it scatters better than blue, we do not notice because of our perception: with the same brightness, blue is perceived by our eyes much better than its counterpart.
That's pretty much how it goes Here is a good video on this topic, which helped us understand this issue:
Let's summarize
- Sunlight, interacting with air molecules, is scattered into different colors.
- Of all the colors, blue is the best for scattering.
- It turns out that he actually captures the airspace.
Of course, the information provided is rather exaggerated and one should focus on many scientific facts and concepts, but it is more or less clear why the sky is blue.
