Why is the sky blue and not green? Why is the sky blue and the sunset red? How to make a sunset out of a blue sky.

The long-awaited, for many, moment has come when the Curiosity rover took a little distraction from science, and just admired the sunset landscape. A few days later, we were able to see this picture as well. Full photo preview on your desktop. Full size on the author's website.

The Martian sunset is unique in that it is blue. The reason for this color of the sky is the same as that on Earth gives a blue sky and a red sunset - Rayleigh scattering. There is a misconception that the blue sky on Earth is due to the presence of oxygen in the air or even the ozone layer. In fact, the composition of the atmosphere is less important here than its density. It is the density of the gas that scatters white sunlight and colors the sky.

The difference between the color of the sky at noon and at sunset is in the volume of the atmosphere that is overcome by the sun's rays. On Mars, the atmosphere is a hundred times thinner than on Earth, but when the sun is near the horizon, its light overcomes a layer of the atmosphere thirty times thicker than at noon.

An additional coloring effect of the Martian sky is given by dust constantly hanging in the atmosphere. Apparently, it is her orange color, in combination with blue, that give a slightly greenish tint in the photo. Although now, on the contrary, the weather is very clear. I have not seen such good visibility in a year and a half that Curiosity has been working on Mars. For the first time, it was possible to see stones on a mountain slope, which is located almost 30 km from the rover.

However, dust is still present in the sky. You can see how the mountain ridge is lost in the dust haze.

In the maximum range available to the eyes, it is located more than 50 kilometers. The clear sky today explains why the sky is almost black at the top of the sunset panorama. During the day at its zenith, it should be the same black as on the Moon or on Earth at an altitude of over 30 km.

The observations carried out by the Viking apparatus show how the color of the sky and its blackness change, depending on the amount of dust.

Let's go back to the color of the sunset. Thanks to modern technology, we can see the dawn even from space. The orange color of the clouds is clearly visible at the border of day and night in the last photograph of “Electro-L”.

Looking at Mars with the Hubble telescope, we can see the same blue border that encircles Mars at the edge of the illuminated disk.

Curiously, blue colors are not always visible in space images of Mars. Apparently, the reason is in seasonal fluctuations in the density of the atmosphere. Depending on the time of year, the reserves of the Martian "air" can fall to 1/150 of the Earth's reserves. The rest freezes in the form of dry ice at the poles.

However, the blue sky, of course, does not surprise us. What is truly incredible is the blue setting sun. As we know from our experience on Earth, at dawn not only changes the color of the sky, but also the visible disk of the star.

Unfortunately, Curiosity does not risk taking direct photographs of the sun, for fear of damaging the camera sensor, but it was able to remove the sun flare, which turned out to be exactly blue.

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 with the time of day.


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 about why this is happening, then the overwhelming majority of us, once armed with school knowledge of physics, are unlikely to be able to answer this simple question. Meanwhile, there is nothing difficult 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 length of the light wave. Our eye is able to distinguish only a fairly narrow range of wave radiation, with the shortest 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.

The white sunbeam is actually made up of waves of all color ranges, as you can easily see by passing it through a glass prism - this school experience you will surely remember. In order to memorize the sequence of changing wavelengths, i.e. the sequence of colors of the spectrum of daylight, 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 during transmission than others. Therefore, when you need to visually highlight some object, they use mainly red, which is clearly visible from afar in any weather.

Therefore, a prohibitive traffic light or any other hazard 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 hit the earth's surface at an angle, not straight. They have to overcome a much thicker layer of the atmosphere than in the daytime, when the earth's surface is illuminated by the direct rays of the sun.

At this time, the atmosphere acts as a color filter that scatters rays of almost the entire visible range, except for the red ones - the longest and therefore the 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 goes down in relation to the horizon, the thicker the layer of the atmosphere has to be overcome by light rays. Therefore, their color is shifting more and more towards the red part of the spectrum. A popular omen is associated with this phenomenon, which says 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. The oblique rays of the sun illuminate the emerging zone of atmospheric radiation, which is much more dust and vapors 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 wavelength of light 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 the atmosphere that they overcome has the smallest thickness.

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

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

This is why we see the sky 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 a city - the sky seems to fade, losing its bright blue.

Gray sky

Now it is clear why autumn storms and winter slush make the sky hopelessly gray. A large amount of water vapor in the atmosphere leads to the scattering of all, without exception, the components of the white light beam. Light rays are split into tiny droplets and water molecules, losing their direction and mixing across the entire spectrum range.


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

Red to violet, which are the main colors of the spectrum. The color visible to the eye is attributed to the length of the light wave. Accordingly, red gives the longest light, and violet the shortest.

During sunset, a person can observe a disc rapidly approaching the horizon. At the same time, sunlight passes through an ever greater thickness. The longer the light wavelength, 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, 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, namely the ability to scatter and absorb. Blue is absorbed more strongly than red, but its ability to dissipate is much higher (four times) than that of red. The ratio of wavelength to light intensity is a proven physical law called the Rayleigh law of the blue sky.

When the sun is high, the layer of atmosphere and suspended matter separating the sky from the eyes of the observer is relatively small, the short wave of blue is not completely absorbed, and the high scattering ability "drowns out" other colors. Therefore, the sky seems blue during the day.

When the time of sunset comes, 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 the same thing is observed at sunrise and for the same reasons.

It is pleasant to look into the dazzling blue sky or enjoy the crimson sunset. Many people enjoy admiring the beauty 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 of 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 looks bright blue. Why it happens?

Scientists have been unable to explain the blue color of the sky for several centuries. From the school physics course, everything that white light with the help of a prism can be decomposed into its constituent colors. For them there is even a simple phrase: "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, blue, purple.

Scientists hypothesized 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 diffused dust 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 reaches the surface of the Earth 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, while photons that give blue color prevail among them. That is why the sky looks blue: the more sunny the day is and the less cloudiness, the more saturated this blue color of the sky becomes.

But if the sky is blue, then why does it turn purple during sunset? The reason for this is very simple. The red component of the solar spectrum is much less 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. At the equator, this angle will be close to right, and closer to the poles, it will decrease. As the Sun moves, the layer of air that the light rays must pass before reaching the observer's eye increases - after all, the Sun is no longer overhead, but tilts toward 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. This 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 stirred up 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 was not confirmed.

Instructions

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 districts of Moscow, people really felt worse. Allergy sufferers and asthmatics have understood the cause of this abnormal phenomenon.

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

What caused the sunset color so unusual for earthlings? It is worth starting with the fact that the atmosphere of Mars is very different from that of the Earth - it has a different composition of gases, a hundred times less density and it is saturated with very fine dust.

Light consists of waves of different lengths, therefore, if you carry out the famous experiment of Newton and catch a sunbeam in a prism, it will decompose into colored rays - into a spectrum. When the sun's rays meet the dust floating in the Martian atmosphere, the same thing happens, but the dust absorbs most of the blue wavelengths. Therefore, the sky on Mars is predominantly red.

But during sunset, if you look directly at the sun, you can see the color blue. This is due to the fact that the rays pass a longer path in the atmosphere than during the day. At this moment, an effect called Rayel scattering begins to act on them - the atmosphere scatters light with a short wavelength stronger than long-wave light. By the way, it is because of this effect and the thick layer of the atmosphere that the sky on our planet is blue.

The effect is clearly visible in photographs from space.

The Opportunity rover was launched to Mars back in 2003 and is managed by NASA's Jet Propulsion Laboratory in Pasadena. The rover holds many records and an open one - for example, it holds the record for the distance traveled on the extraterrestrial surface (the second place - however, the data differ - is occupied by the Soviet "Lunokhod-2"). Opportunity has already covered almost 42 kilometers, although, as the project staff note, 11 years ago, when it launched its first mission, no one expected such results. The rover is currently exploring the edge of the 22-kilometer-long Endeavor Crater to explore the western edge as well as clay mineral deposits that have been exposed to liquid water in the past.

The rover has a twin brother, the Spirit rover, which landed 3 weeks apart in 2004. The rovers have found abundant evidence of a planet of water on the surface in the past, but Spirit stopped communicating in 2010 and declared its mission complete in 2011.

In addition to Opportunity, the Red Planet is currently being explored by the Curiosity rover, which launched in 2011 and landed in 2012. NASA interplanetary station is conducting research from orbit MRO (Mars Reconnaissance Orbiter) NASA Orbital Probe Mars odyssey, ESA interplanetary station Mars express as well as NASA's 10th Mars Orbiter MAVEN and Indian interplanetary station Mangalyaan (Mars Orbiter Mission), which is the first Indian spacecraft launched to another planet. MAVEN and Mangalyaan reached the orbit of the planet almost simultaneously - in September 2014.

The sun not only gives us light and warmth, but also paints everything around us in the rainbow colors of the spectrum. A ray of white light is actually multi-colored, as we know from its reflection in a raindrop, which has become a rainbow. Then why did the sun choose blue for the sky, and not green, for example? Although it is very difficult to imagine a green sky.
The earth is surrounded by a layer of air that we breathe. It contains oxygen, ozone and carbon dioxide. This layer is called the atmosphere. The thickness of the atmospheric layer is about 500 kilometers. It contains the air we breathe.

Air consists of molecules in which light cannot be reflected. It dissipates on them. The electrons in the molecule are exposed to sunlight and begin to emit it. And the light itself is scattered. And we see this diffused light from the Earth.

The gases in the air divide light into the colors of the spectrum known to us. We know them well - red, orange, yellow, green, blue, blue, purple. But we, most often, see blue or light blue. Why the sky is blue?

This is where Rayleigh's law of scattering comes into play, according to which light with shorter wavelengths scatters faster than light with longer wavelengths. The blue, cyan and violet colors of the spectrum have shorter wavelengths. Therefore, it is their diffused light that we see in the sky.

Some colors of the spectrum with longer wavelengths, such as red and orange, hardly scatter. At sunset, the layer of the atmosphere increases many times, it is more difficult for the spectrum to pass through it, and since the blue and blue colors have scattered, they remain less and less in the palette of heavenly colors by evening, one paint remains intact - red. Here we see her at sunset in the sky. And the sun itself appears to us then red. Of course, in another part of the planet, the sky is blue at this moment, short rays of the spectrum are scattered there.

By morning, the sun returns to us, if it does not have to break through a thick curtain of clouds and clouds. Then we see the sky in clouds. And this is a completely different story.