The light of the Sun is one of the most important things on Earth. It supports life in every organism on our planet, and without it we simply would not exist. But how does it affect us? And why does the Sun shine at all? Let's find out how these processes work.
Another star in the sky
In ancient times, people did not know why the Sun shines. But even then they noticed that it appears early in the morning and disappears in the evening, and is replaced by bright stars. He was considered a daytime deity, a symbol of light, goodness and power. Now science has stepped far forward and the Sun is no longer so mysterious to us. Dozens of websites and books will tell you a lot of details about him, and NASA will even show pictures of him from space.
Today we can safely say that the Sun is not some special and unique object, but a star. The same as thousands of others that we see in the night sky. But other stars are very far from us, so from Earth they appear as tiny lights.
The sun is much closer to us, and its radiance is visible much better. It is the center of the star system. Planets, comets, asteroids, meteoroids and other cosmic bodies revolve around it. Each object moves in its own orbit. The planet Mercury has the shortest distance to the Sun; the farthest parts of the system have not been explored. One of the distant objects is Sedna, which makes a full revolution around the star every 3420 years.
Why does the sun shine?
Like all other stars, the Sun is a huge hot ball. It is believed to have formed from the remains of other stars about 4.5 billion years ago. The gas and dust released from them began to compress into a cloud, the temperature and pressure in which were constantly increasing. Having “warmed up” to about ten million degrees, the cloud turned into a star, which became a giant energy generator.
So why does the sun shine? All this is due to thermonuclear reactions inside it. At the center of our star, hydrogen is continuously converted into helium under the influence of very high temperatures - about 15.7 million degrees. As a result of this process, a huge amount of thermal energy is generated, accompanied by a glow.
Thermonuclear reactions take place only in the solar core. The radiation it produces spreads around the star, forming several outer layers:
- radiative transfer zone;
- convective zone;
- photosphere;
- chromosphere;
- crown
Sunlight
Most visible light is produced in the photosphere. This is an opaque shell, which is identified with the surface of the Sun. The temperature in Celsius of the photosphere is 5,000 degrees, but there are also “colder” areas on it, called spots. In the upper shells the temperature increases again.
Our star is a yellow dwarf. This is far from the oldest and not the largest star in the Universe. In its evolution, it has reached about halfway and will live in this state for about another five billion years. The Sun will then turn into a red giant. And then it will shed its outer shell and become a dim dwarf.
The light it emits now is almost white. But from the surface of our planet it is visible as yellow, as it scatters and passes through the layers of the earth’s atmosphere. The color of the radiation becomes close to real in very clear weather.
Interaction with the Earth
The location of the Earth and the Sun relative to each other is not the same. Our planet constantly moves around the star in its orbit. It makes a full revolution in one year or approximately 365 days. During this time, it covers a distance of 940 million kilometers. No movement is felt on the planet itself, although it travels approximately 108 kilometers every hour. The consequences of such a journey manifest themselves on Earth in the form of changing seasons.
However, the seasons are determined not only by the movement around the Sun, but also by the tilt of the earth's axis. It is tilted 23.4 degrees relative to its orbit, so different parts of the planet are not equally illuminated and warmed by the star. When the Northern Hemisphere is turned towards the Sun, it is summer, and in the Southern Hemisphere it is winter at the same time. Six months later, everything changes exactly the opposite.
We often say that the Sun appears during the day. But this is just an expression, because it creates our day. Its rays break through the atmosphere, illuminating the planet from morning to evening. Their brightness is so strong that we simply cannot see other stars during the day. At night, the Sun does not stop shining, the Earth simply turns to it first on one side or the other, because it rotates not only in orbit, but also around its own axis. It makes a full revolution in 24 hours. On the side facing the luminary there is day, on the opposite side there is night, they change every 12 hours.
Irreplaceable Energy
From our planet, the distance to the Sun is 8.31 light years or 1.496·10 8 kilometers, which is quite enough for the existence of life. A closer location would make the Earth look like a lifeless Venus or Mercury. However, in a billion years the star should become 10% hotter, and in another 2.5 billion years it will be able to literally dry out all life on the planet.
Currently, the temperature of the star suits us perfectly. Thanks to this, a huge variety of life forms has appeared on our planet, ranging from plants and bacteria to humans. They all need sunlight and warmth, and will easily die if left for a long time. Starlight promotes photosynthesis in plants, which produces vital oxygen. Its ultraviolet radiation enhances the immune system, promotes the production of vitamin D, and helps cleanse the atmosphere of harmful substances.
The uneven heating of the Earth by the Sun creates the movement of air masses, which, in turn, creates the climate and weather on the planet. Light from a star affects the establishment of circadian rhythms in living organisms. That is, a strict dependence of their activity on the change of time of day is developed. So, some animals are active only during the day, others only at night.
Observing the Sun
Among the star systems closest to us, the Sun is not the brightest. It ranks only fourth in this indicator. For example, the star Sirius, which is clearly visible in the night sky, is as much as 22 times brighter than it.
Despite this, we cannot look at the Sun with the naked eye. It is too close to Earth and observing it without special instruments is harmful to vision. For us, it is about 400 thousand times brighter than the light reflected by the Moon. We can look at it with the naked eye only at sunset and dawn, when its angle is small and the luminosity drops thousands of times.
The rest of the time, to see the Sun, you need to use special solar telescopes or light filters. If you project the image onto a white screen, then it is possible to see spots and flashes on our light even with unprofessional equipment. But this must be done carefully so as not to damage it.
The fourth state of matter.
Part six. Why does the sun shine
Why does the sun shine? The same exact answer to this question is known today. The sun shines because in its depths, as a result of the thermonuclear reaction of converting 4 protons (nuclei of hydrogen atoms) into one helium nucleus, free energy remains (since the mass of the helium nucleus is less than the mass of four protons), which is emitted in the form of photons. Photons in the visible range are the sunlight we see.
Now let’s speculate and imagine the path that scientists have taken. And at the same time, let’s think about what will happen when hydrogen completely burns out in the Sun? Will it definitely go out? We advise you to read the article to the end - a very interesting assumption is made there.
Let us assume that the Sun burns the most calorific of all types of fuel - the purest carbon, which burns entirely, without any ash. Let's do a simple calculation. It is known how much heat this “fire” sends to the Earth. The sun is a globe, so it emits heat evenly in all directions. Knowing the sizes of the Earth and the Sun, it is not difficult to calculate that in order to maintain the flow of heat from the Sun, about 12 billion tons of coal must burn in it every second! The figure is huge on an earthly scale, but for the Sun, which is more than three hundred thousand times heavier than the Earth, this amount of coal is small. And yet all this coal on the Sun would have to burn out in just six thousand years. But the data of many sciences - geology, biology, etc. - irrefutably indicate that the bright Sun has been heating and illuminating our planet for at least several billion years.
The idea that the sun burns with coal had to be rejected. But maybe there are chemical reactions that release even more heat than when burning coal? Let's assume they exist. But even these reactions could extend the life of the Sun by a thousand, two thousand years, even doubled, but no more.
But if the Sun is not able to provide itself with fuel for any long time, then perhaps outer space does this from the outside? It has been suggested that meteorites are constantly falling onto the Sun. We have already said that when approaching the Earth, meteorites, due to braking in the Earth’s atmosphere, often completely burn out, heating the air along the way. Why not assume that there is no atmosphere around the Sun, that the braking of meteorites occurs directly in the solar matter, and it heats up to a high temperature?
Let's turn again to the calculations. How many meteorites must fall on the Sun to ensure its long-term burning? The calculation gives an absolutely incredible figure: even if the weight of all the meteorites that fell on the Sun was equal to the weight of the Sun itself, it would still shine for only about a million years.
But maybe once upon a time such a huge number of meteorites fell on the Sun, heated it to a huge temperature, and now the Sun is slowly cooling? Nothing like this! There is a lot of evidence that the Sun shone and warmed a billion, a million, and a thousand years ago, just as it does today. So, the second assumption also fails.
The amazing constancy of solar activity also buried the third, most tempting assumption about the cause of the “burning” of the Sun. It boiled down to the following. According to the law of universal gravitation, all bodies move closer to each other. The Earth is attracted by the Sun and moves around it. The stone is attracted by the Earth and falls on it if it is released from the hands.
Let's imagine that the Sun is some kind of huge vessel with gas. The molecules of this gas, subject to the action of mutual attraction, despite the collisions that throw them away from each other, must gradually attract each other and come closer. The sun as a whole would then shrink, the gas pressure in it would increase, and this would lead to an increase in temperature and the release of heat.
If we assume that over 100 years the diameter of the Sun decreases by only a few kilometers, then this phenomenon could completely explain the emission of radiation from the Sun. However, such a slow reduction cannot be detected using astronomical instruments.
But there is a “device” that works for a much longer time. This device is the Earth itself. During its existence, the Sun would have to shrink tens of times: from a size many times greater than the extent of the entire solar system to its present size. Such compression would certainly affect . However, the history of the Earth knows nothing like this. She knows of major geological disasters in which the highest mountains perished, new oceans and entire continents were born, but all this can be fully explained by the activity of the Earth itself, and not the Sun.
So, all three mentioned hypotheses about the reasons for the “burning” of the Sun turned out to be untenable. Science, which managed to explain many of the most complex phenomena on Earth, gave up for a very long time before the mystery of the activity of the Sun. Now it has become clear that the solution to this riddle must be sought not in the depths of space, but in the depths of the Sun.
And here the science of the super-large - astronomy - came to the aid of the science of the super-small - the physics of the atomic nucleus.
Stars emit enormous amounts of heat and light over many billions of years, requiring enormous fuel consumption. Until the twentieth century, no one could imagine what kind of fuel it was. The biggest problem in physics was the big question: where do stars get their energy? All we could do was look at the sky and realize that there was a huge “hole” in our knowledge. To understand the secret of the stars, a new engine of discovery was needed.
Helium was needed to unlock the secret. Albert Einstein's theory proved that stars can obtain energy from within atoms. The secret of the stars is Einstein's equation, which is the formula E = ms 2. In a sense, the number of atoms that make up our body is concentrated energy, compressed energy, energy compressed into atoms (cosmic dust particles) that make up our universe. Einstein proved that this energy could be released by colliding two atoms. This process is called thermonuclear fusion, and it is this force that powers stars.
Imagine, but the physical properties of a small, subatomic particle determine the structure of stars. Thanks to Einstein's theory, we have learned how to release this energy inside the atom. Now scientists are trying to simulate the source of stellar energy to gain control of the power of fusion in the laboratory.
Within the walls of the laboratory, near Oxford in England, there is a machine that Andrew Kirk and his team are turning into a “star” laboratory. This installation is called Tokamak. In essence, it is a large magnetic bottle that holds very hot plasma, thanks to which it is possible to simulate conditions similar to those inside a star.
Inside the Tokamak, hydrogen atoms confront each other. To smash atoms into each other, the Tokamak heats them to 166 million degrees, at which temperature the atoms move so fast that they cannot avoid colliding with each other. Heating is movement; the movement of heated particles is sufficient to overcome the repulsive force. Flying at thousands of kilometers per second, these hydrogen atoms crash into each other and combine to form a new chemical element, helium, and a small amount of pure energy.
Hydrogen weighs slightly more than helium; during combustion, mass is lost, and the lost mass is converted into energy. A tokamak can support fusion for a fraction of a second, but in the interior of a star the fusion of nuclei does not stop for billions of years, the reason is simple - the size of the star.
A star lives by gravity. That's why stars are big, huge. To collapse a star, a huge force of gravity is needed in order to release an incredible amount of energy, sufficient for thermonuclear fusion. This is the secret of the stars, this is why they glow.
Fusion in the core of the Sun's star generates enough power every second to power a billion nuclear bombs. A star is a giant hydrogen “bomb”. Why then doesn't she just fly to pieces? The fact is that gravity compresses the outer layers of the star. Gravity and synthesis are waging a grandiose war, the gravity of which wants to crush the star and the energy of synthesis, which seeks to destroy the star from the inside, this conflict and this balance create the star.
This struggle for power continues throughout the star’s life. It is these battles on the stars that create light and each ray of star travel makes an incredible journey, the light travels 1080 million kilometers per hour. In one second, a beam of light can circle the earth seven times; nothing in the universe moves so fast.
Since most stars are very far away, light takes hundreds, thousands, millions and even billions of years to reach us. When the orbiting Hubble Space Station peers into the far reaches of our universe, it sees light that has been traveling for billions of years. The light of the star Etequilia, which we see today, set off 8 thousand years ago, the light of Betelgeuse has been traveling since Columbus discovered America 500 years ago. Even the light of the Sun flies to us for 8 minutes.
When the sun synthesizes helium from hydrogen, a particle of light is created - a photon. This ray of light has a long and difficult path to the surface of the Sun. The whole star prevents him, when a photon appears, it crashes into another atom, another proton, another neutron, it doesn’t matter, it is absorbed, then reflected in another direction, and moving so chaotically inside the Sun, it must break out.
The photon will have to rush around madly, crash into gas atoms billions of times and desperately rush out. It's funny, it takes a photon thousands of years to get out of the Sun's core and only 8 minutes to fly from the surface of the Sun to the Earth. Photons are sources of heat and light that support the diverse and amazing life on our planet Earth!
I think it’s no secret to anyone that our sun and the stars that we see in the sky at night are the same. But the “night” stars are much further away from us than the sun.
Stars- These are huge spherical clusters of hot gas. As a rule, stars consist of more than 99% from gas, the remaining fractions of a percent account for a huge number of elements (for example, there are about 60 of them in our sun). The surface temperatures of different types of stars range from 2,000 to 60,000 degrees Celsius.
What makes stars emit light? Ancient thinkers thought that the surface of the sun was constantly burning, and therefore radiated light and heat. However, it is not. Firstly, the reason for the emission of heat and light is located much deeper than the surface of the star, namely in core. And secondly, the processes occurring in the depths of stars are not at all similar to combustion.
The process occurring in the interior of stars is called. In a nutshell, thermonuclear fusion is the process of converting matter into energy, and an incredible amount of energy is released from a minimal amount of matter.
From a scientific point of view, this is a reaction in which lighter atomic nuclei - usually hydrogen isotopes(deuterium and tritium) merge into heavier nuclei - helium. For this reaction to occur, an incredibly high temperature is required - several million degrees.
This reaction occurs in our sun: at a core temperature of 12,000,000 degrees, 4 hydrogen atoms merge into 1 helium nucleus and an unimaginable amount of energy is released: heat, light and electromagnetism.
How could you guess the sun forever, it will “burn itself” over time. Scientists believe that there is still enough matter in it for approximately 4-6 billion years, i.e. somewhere as long as it has already existed.
A growing person is interested in literally everything. He asks questions about everything he sees. Why does the sun shine during the day and the stars at night? And so on and so forth. Answering seemingly simple questions is not always easy. Because sometimes some special knowledge is missing. And how can we explain something complex in a simple way? Not everyone can do this.
What is a star?
Without this concept, it is impossible to clearly explain why the sun shines during the day and the stars at night. Children often imagine stars as small dots in the sky, which they compare to small light bulbs or lanterns. If we draw an analogy, they can be compared to huge spotlights. Because the stars are unimaginably huge, incredibly hot and located at such a distance from us that they seem crumbs.
What is the sun?
First, you need to tell us that the Sun is a name, like a name. And the star closest to our planet bears this name. But why isn't it a point? And why does the sun shine during the day and the stars at night, if they are the same?
The sun does not appear to be a point because it is much closer than the others. Although it is also far from it. If you measure the distance in kilometers, the number will be equal to 150 million. A car will travel this distance in 200 years if it moves without stopping at a constant speed of 80 km/h. Due to its incredibly large distance, the sun appears small, although it is such that it could easily accommodate a million planets similar to Earth.
By the way, the sun is far from the largest and not very bright star in our sky. It is simply located in the same place as our planet, and the rest are scattered far in space.
Why is the sun visible during the day?
First you need to remember: when does the day begin? The answer is simple: when the sun begins to shine over the horizon. Without his light this is impossible. Therefore, answering the question of why the sun shines during the day, we can say that the day itself will not come if the sun does not rise. After all, as soon as it goes beyond the horizon, evening comes, and then night. By the way, it is worth mentioning that it is not the star that moves, but the planet. And the change from day to night occurs due to the fact that planet Earth rotates without stopping around its fixed axis.
Why are the stars not visible during the day if they, like the sun, always shine? This is explained by the presence of an atmosphere on our planet. In the air they dissipate and outshine the faint glow of the stars. After it sets, the scattering stops, and nothing blocks their dim light.
Why the moon?
So, the sun shines during the day and the stars at night. The reasons for this are in the air layer surrounding the earth. But why is the moon sometimes visible, sometimes not? And when it is there, it can take on different forms - from a thin sickle to a bright circle. What does this depend on?
It turns out that the moon itself does not glow. It works like a mirror that reflects the sun's rays onto the ground. And observers can see only that part of the satellite that is illuminated. If we consider the whole cycle, it begins with a very thin month, which resembles an inverted letter “C” or an arc from the letter “P”. Within a week it grows and becomes like half a circle. Over the next week it continues to increase and every day it gets closer to a full circle. Over the next two weeks, the pattern decreases. And at the end of the month, the moon completely disappears from the night sky. More precisely, it is simply not visible, because only that part of it that turned away from the Earth is illuminated.
What do people see in space?
Astronauts in orbit are not interested in the question of why the sun shines during the day and the stars at night. And this is due to the fact that both are visible there at the same time. This fact is explained by the absence of air, which prevents light from the stars from passing through the scattered rays of the sun. You can call them lucky because they can immediately see both the nearest star and those that are far away.
By the way, night lights differ in color. Moreover, this is clearly visible even from Earth. The main thing is to look closely. The hottest ones glow white and blue. Those stars that are cooler than the previous ones are yellow. These include our Sun. And the coldest ones emit red light.
Continuing the conversation about the stars
If the question of why the sun shines during the day and the stars at night arises among older children, then you can continue the conversation by remembering the constellations. They combine groups of stars that are located in one place on the celestial sphere. That is, they seem to be located nearby to us. In fact, there may be a huge distance between them. If we could fly far from the solar system, we would not recognize the starry sky. Because the outlines of the constellations would change greatly.
In these groups of stars the outlines of human figures, objects and animals were seen. In this regard, various names appeared. Ursa Major and Ursa Minor, Orion, Cygnus, Southern Cross and many others. Today there are 88 constellations. Many of them are associated with myths and legends.
Because of the constellation, they change their position in the sky. And some are generally visible only in a certain season. There are constellations that cannot be seen in the Northern or Southern Hemisphere.
Over time, the constellations lost minor stars, and from their patterns it became difficult to guess how the name came about. The most famous constellation in the Northern Hemisphere, Ursa Major, has now turned into a “bucket”. And modern children are tormented by the question: “Where is the bear?”