Despite scientific progress and free access to many sources of information, it is rare that a person can correctly answer the question of why the sky is blue.
Why is the sky blue or blue during the day?
White light - which is what the Sun emits - is made up of seven parts of the color spectrum: red, orange, yellow, green, blue, indigo and violet. The little rhyme known from school - “Every Hunter Wants to Know Where the Pheasant Sits” - precisely determines the colors of this spectrum by the initial letters of each word. Each color has its own wavelength of light: red is the longest and violet is the shortest.
The sky (atmosphere) familiar to us consists of solid microparticles, tiny drops of water and gas molecules. For a long time, there have been several erroneous assumptions trying to explain why the sky is blue:
- the atmosphere, consisting of tiny particles of water and molecules of various gases, allows the rays of the blue spectrum to pass through well and does not allow the rays of the red spectrum to touch the Earth;
- Small solid particles - such as dust - suspended in the air scatter blue and violet wavelengths 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 research by the English physicist John Rayleigh showed that solid particles are not the main cause of light scattering. It is the molecules of gases in the atmosphere that separate light into color components. A white ray of sunlight, colliding with a gas particle in the sky, scatters (scatters) in different directions.
When it collides with a gas molecule, each of the seven color components of white light is scattered. At the same time, light with longer waves (the red component of the spectrum, which also includes orange and yellow) is scattered less well 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 waves. In addition, our eyes perceive blue color better than violet, given the same brightness of both. It is these facts that determine the color scheme of the sky: the atmosphere is literally filled with rays of blue-blue color.
Why then is the sunset red?
However, the sky is not always blue. The question naturally arises: if we see blue skies all day, why is the sunset red? We found out above that red color is least scattered by gas molecules. During sunset, the Sun approaches the horizon and the sun's ray is directed towards the Earth's surface not vertically, as during the day, but at an angle.
Therefore, the path 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 the 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, heated at the surface of the earth, rises and expands due to the fact that the air pressure is less at the top. As the air expands, it cools. When it reaches a certain temperature, water vapor condenses around atmospheric dust and other suspended solids, resulting in tiny droplets of water that coalesce to form a cloud.
Despite their relatively small size, water particles are much larger than gas molecules. And if, when meeting air molecules, the sun's rays are scattered, then when they meet water droplets, the light is reflected from them. In this case, the initially white ray of sunlight does not change its color and at the same time “colors” the molecules of the clouds white.
It is difficult to answer the question why the sky is blue and the sunset is red.
Why is this happening?
Scientists for several centuries could not explain the blue color of the sky.
From a school physics course, everyone knows that white light can be separated into its component colors using a prism.
There is even a simple phrase to remember them:
The initial letters of the words in this phrase help you remember the order of colors in the spectrum: red, orange, yellow, green, blue, indigo, violet.
Scientists have suggested that the blue color of the sky is caused by 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 continued, and in 1899 Lord Rayleigh put forward a theory that finally answered 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 reaches the Earth's surface without interference, but most of them are absorbed by air molecules. By absorbing photons, air molecules become charged (excited) and then emit photons themselves. But these photons have a different wavelength, and photons that produce blue predominate among them. This is why the sky looks blue: the sunnier the day and the less cloudy it is, the more saturated this blue color of the sky becomes.
But if the sky is blue, then why does it turn crimson during sunset? The reason for this is very simple. The red component of the solar spectrum is absorbed much worse 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 right angle, closer to the poles it will decrease. As the Sun moves, the layer of air that light rays must pass through before reaching the observer's eye increases - after all, the Sun is no longer overhead, but is leaning towards the horizon. A thick layer of air absorbs most of the rays of the solar spectrum, but red rays reach the observer almost without loss. This is why the sunset looks red.
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 don’t even think about why the sky changes color as the time of day changes.
We are accustomed to the bright blue on a fine sunny day and to the fact that in the fall the sky becomes hazy gray, losing its bright colors. But if you ask a modern person why this happens, 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 the school physics course we should know that differences in the color perception of objects depend on the wavelength of light. Our eye is able to distinguish only a fairly narrow range of wave radiation, with the shortest waves being blue and the longest being red. Between these two primary colors lies our entire palette of color perception, expressed by wave radiation in different ranges.
A white ray of sunlight actually consists of waves of all color ranges, which is easy to see by passing it through a glass prism - you probably remember this school experience. In order to remember the sequence of changes in wavelengths, i.e. sequence of colors of the daylight spectrum, a funny phrase about a hunter was invented, which each of us learned at school: Every Hunter Wants to Know, etc. 
Since red light waves are the longest, they are less susceptible to scattering when passing through. Therefore, when you need to visually highlight an object, they use predominantly red color, which is clearly visible from afar in any weather.
Therefore, a prohibitory traffic light or any other danger 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 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 rays from almost the entire visible range, except for red ones - the longest and therefore most resistant to interference. All other light waves are either scattered or absorbed by particles of water vapor and dust present in the atmosphere.
The lower the Sun falls relative to the horizon, the thicker the layer of atmosphere the light rays have to overcome. Therefore, their color is increasingly shifting towards the red part of the spectrum. A folk superstition is associated with this phenomenon, saying that a red sunset foretells a strong wind the next day. 
The wind originates in high layers of the atmosphere and at a great distance from the observer. Oblique rays of the sun highlight the emerging 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 light wavelengths also explain the clear blue of the daytime sky. When the sun's rays fall directly on the surface of the earth, the layer of atmosphere they overcome has the smallest thickness.
Scattering of light waves occurs when they collide with the molecules of gases that make up the air, and in this situation, the short-wavelength light range turns out to be the most stable, i.e. blue and violet light waves. On a fine, windless day, the sky acquires amazing depth and blueness. But why do we then see blue and not violet in the sky?
The fact is that the cells in the human eye that are responsible for color perception perceive blue much better than violet. Still, violet is too close to the border of the perception range.
This is why we see the sky as bright blue if there are no scattering components in the atmosphere other than air molecules. When a sufficiently large amount of dust appears in the atmosphere - for example, in a hot summer in the city - the sky seems to fade, losing its bright blue.
Gray sky of bad weather
Now it’s clear why autumn bad weather and winter slush make the sky hopelessly gray. A large amount of water vapor in the atmosphere leads to the scattering of all components of a white light beam without exception. Light rays are crushed into tiny droplets and water molecules, losing their direction and mixing throughout the entire range of the spectrum. 
Therefore, light rays reach the surface as if passed through a giant scattering lamp. We perceive this phenomenon as the grayish-white color of the sky. As soon as moisture is removed from the atmosphere, the sky again becomes bright blue.
Read this:
November 6, 2011 The sunset over Los Angeles was almost blood red and the Sun was huge. The sky surrounding the Sun was also bright orange-red. It was an amazing sight. People stopped on the road to watch him. I guess this is Planet X getting closer? And the redness was due to the tail, and the increase in the Sun was also due to the red color of the dust? [and from another] November 5, 2011 This photo was taken just before sunrise near Kokomo, Indiana. Since late summer last year I have often seen pink clouds like these and increasingly blood red pre-dawn skies on clear days. November 3, 2011 This photo on a cloudy day was taken about an hour after sunrise, note that the sun is peeking through the clouds and that the clouds near the horizon are pink. About two and a half hours after sunrise, slightly pink clouds could still be seen near the horizon, as in this photo, although at that moment I had not yet taken a single photo. Usually the pink color disappears shortly after dawn. It was cloudy this afternoon and I noticed the clouds turning pink a couple of hours before sunset. If the tail of Planet X began to reach the Earth, would the clouds become more pink during the day or the sky more red when it is a little hazy and overcast?
Humanity is accustomed to the fact that the rising and setting Sun is larger than the midday Sun, and the Sun at sunrise and sunset, as well as the surrounding clouds, are orange. We explained that this is due to the easier bending of light in the red region of the spectrum, so red light rays bend primarily above the horizon due to Earth's gravity, while light from other parts of the spectrum does not bend as much. Light from this part of the spectrum, which comes from the Sun in all directions, is bent by Earth's gravity so that light that would normally pass from either side of an observer on Earth is bent toward its center. Therefore, it comes to the observer's eye or camera both from the sides and directly in a straight line from the Sun, painting a broader picture.
How will this change as the amount of red dust from Planet X's tail increases in the atmosphere? Obviously, any light penetrating the atmosphere will increasingly shift towards the red region of the light spectrum. Dust appears red because it primarily reflects light from the red region of the spectrum, while absorbing light from other regions of the spectrum. So what will the effect be, given that the sunlight that reaches Earth will increasingly fall into the red region of the light spectrum? Of course, red auroras have been observed in North America recently in part due to the gravitational dance between Earth and Planet X. Will other distortions occur?
As an attentive observer noted, at sunset the Sun appears larger than usual. If the light of the red spectrum, after leaving the Sun, is deflected towards the Earth, what will the increased amount of red dust in the Earth's atmosphere do with these rays of light coming from the Sun to the Earth? We can expect their additional deflection towards the Earth's gravitational center, with an even larger apparent size of the Sun at sunrise and sunset. The sizes of all planetary objects may be distorted. The moon may appear larger and thus closer, sometimes disturbing observers. The authorities will have no explanation for this and, as usual, will remain silent without offering anything. NASA and experts will be further embarrassed, and more worried people will begin to scour the internet for answers, as red dust is mentioned in Doomsday prophecies and its appearance cannot be hidden.
Sometimes at night we have the opportunity to observe a phenomenon in which the sky seems not dark enough. And today we will look at questions about why the sky is bright at night.
Why is it light at night in winter?
In the winter period of the year, we are accustomed not only to the fact that it begins to get dark much earlier than in summer, but also to the fact that the weather is usually such that even in the daytime the daylight hours seem less bright. Despite this, sometimes we have the opportunity to observe fairly bright nights, so we need to consider the question of why the sky is bright at night in winter.
There may be two reasons for a lighter sky at night:
- If you notice that the night is not as dark as always, and there is precipitation in the form of snow outside, you can be sure that the snow is the reason for such a bright sky. Snowflakes reflect the light of lanterns, as well as moonlight, thereby creating the illusion of a more illuminated night sky;
- If the sky is bright enough and there is no precipitation, then the cause of this phenomenon can be considered strong and low cloudiness. Pay attention to the clouds - they are lower than usual. For this reason, clouds act as reflectors of light from the earth, which leads to the illusion of a bright sky.
Why is it as bright as day at night?
If, when wondering about the night illumination of the Earth’s surface, you were directly interested in information about the so-called “White Nights”, which are observed, for example, in St. Petersburg, then in this situation the answer will be completely different.
To begin with, it is worth noting that such white nights are observed not only in St. Petersburg, but also in many other parts of our planet. For example, it is quite possible that someone will be interested in the question of why it is light at night in Greenland, since a similar phenomenon is also present there.
Events on a planetary scale are considered to be to blame for the occurrence of such a phenomenon. The fact is that at a certain point in time, due to the fact that the Earth rotates around the Sun along a certain trajectory, and also rotates around its own axis, our planet is on such a trajectory that even at night the Sun is in the territory, for example, St. -Petersburg or Greenland does not set much below the horizon. Accordingly, even at night, sunlight is scattered over the surface of the Earth and in the above-mentioned territories a kind of twilight is observed instead of the usual night.
