Why it is dark at night: a scientific explanation.

To the question why is it dark at night, surely many will be able to give the correct answer. However, memory can fail everyone. Therefore, we decided to refresh our memory school course astronomy, and at the same time remind you of how day follows night. This knowledge will be useful, for some it will simply be interesting to show off, so to speak, their intelligence in front of society, while for others the child will grow to the age of “why” and will ask all sorts of questions to which it will be necessary to give answers that are understandable to him.

As everyone knows, the earth is round in shape and rotates around its axis. When it is light on one half of the earth, it is dark on the other. The sun can only illuminate one hemisphere. So, to understand why day follows night, you need to understand two processes.

Process one. Our planet rotates like a spinning top and this happens non-stop and at tremendous speed. Scientists have calculated the speed of rotation of the earth, it is 1666 km/h. It is at this speed that the earth makes a full revolution around its axis per day (24 hours). We do not feel this movement because the surface area of ​​the earth is very large (slightly more than 510 million km²).

Process two. The only source of light and heat on Earth (and on the other eight planets) is the Sun, which sends its ray streams to the planets. Precisely because the Earth is constantly moving, sun rays always illuminated different corners globe. People observe this phenomenon, but it looks as if the sun is moving across the sky, i.e. V different times located in different places during the day. However, it is not the Sun that moves, but the Earth and the light hits a new place. Gradually, during the day, the Earth turns the other side to the Sun and at the same time the first hemisphere goes into shadow. As this happens, the light becomes less and less, and eventually night falls. And on the opposite side, on the second hemisphere, day comes. This is how the process of changing day to night and night to day occurs.

If someone asks you, why is it dark at night, you just boldly answer him that the Earth has “turned away” from the Sun.

Indeed, why is the sky dark at night? Try to answer! It turns out that you can’t just say: it’s dark at night because there’s no light. This answer is incorrect. Even without the Sun, the sky, it would seem, “has no right” to be dark. Judge for yourself.

"BAN" ON DARKNESS

This is the sun. Some are close and therefore bright, others are unimaginably distant from us, almost invisible, or even completely inaccessible to our eyes. But each one radiates light. And if there are countless stars, then all together they give an infinite amount of light. It doesn’t matter that individually other stars are invisible. Since there are infinitely many of them above any, even the tiniest, corner of the sky, they must merge everywhere, creating a continuous background, sparkling with a dazzling brilliance, emitting an infinite amount of radiant energy. In short, the entire sky is prescribed to have a brightness no less than that of the surface of the Sun. And since the light of the stars is caused by them high temperature, the sky must pour out the same unbearable heat.

And if so, then there should be no place in the world either for or for people. Life is unthinkable in the unbearable light and heat. Any leaf, any insect would instantly be incinerated in such a thing. The substance of our usual states - solid, liquid - would become impossible. Everywhere would be as hot as in the depths of the Sun. An unexpected conclusion. And, of course, completely wrong.

Science has been trying to refute it for more than a hundred years. A lot of attempts have been made. Maybe the light is absorbed by the interstellar medium - gas, dark dust, cold planets, cooled “corpses” of stars? No, no matter how much light is absorbed, there will still be an infinite amount of it. The calculation is simple: no matter how large the proportion of non-luminous matter is, there will still be an infinite amount of luminous matter. Divide infinity in half, into ten, a hundred, a thousand parts - any part will still be infinitely large. In addition, the atoms of the interstellar medium do not “eat up” light without leaving a trace. They simply swallow it and then “spit it out” in another direction. They only dissipate, as if scattering energy throughout the world.

Then maybe there are giant opaque shells in our universe? One of Chekhov’s heroes philosophized: “Perhaps our entire universe is hidden in the hollow tooth of some huge monster.” And this “hypothesis,” no matter how seriously it is presented, does not solve the problem, but only pushes it back. After all, any “hollow”, any dark shell in an infinitely light and hot world would inevitably melt and evaporate.

It remains to make one more, very risky assumption: to lift the ban on night darkness by abandoning its main reason - stellar infinity. Recognize that in the infinite space of the universe there are only a “handful” of stars and galaxies - and everything will fall into place, right?

No, not like that. In such a conclusion there is philosophical cheating and physical thoughtlessness. Even the great classic of natural science, Isaac Newton, said that there cannot but be an infinite number of stars. If there were only a “handful” of them, albeit a huge one, thanks to them they would stick together into one single giant celestial body. Later, however, physics made an amendment: a “handful” of stars would not stick together, but, on the contrary, would scatter throughout infinite space. And then the Universe would be empty, virtually all matter would disappear from it.

But there is substance! No matter how far telescopes look, they find matter everywhere. So there are infinitely many stars? It turns out like this. Then why is it still dark at night? See how confused everything is! Trying to comprehend the appearance of the sky, we got lost in the jungle of contradictions, faced ideological questions, and touched upon the greatest problem of the structure of the entire Universe - a science called cosmology.

HIERARCHY OF SYSTEMS

You received a task on an exam and were horrified by its difficulty. But in exam papers It is not customary to ask unsolvable problems. That's why you stubbornly wrinkle your forehead, think painfully, and finally solve the problem! And then you look for another, and a third, and a general method of solution. Something similar happens in cosmology. Knowing that the mystery of the darkness of the night can certainly be solved (the sky is dark!), astronomers, physicists, and philosophers are persistently looking for a solution. And little by little the darkness of the night begins to gain the right to exist.

Let's imagine this: the world is infinite, there are countless stars in it, but, nevertheless, the density of matter in the infinite volume of the Universe is zero. Impossible? It turns out it's possible. It is only necessary that as the volume of outer space increases, the density of matter in it decreases.

The density of a substance is mass divided by volume. Each star has a very high density, because its entire volume is filled with matter. But in a volume that includes two neighboring stars, the average density of matter is less (after all, cosmic matter between stars weighs practically nothing). The density of matter in the volume of the Galaxy is even much lower. What next? What if in the limiting case - for an infinitely large volume - we formally obtain zero matter density? After all, then the ban on darkness at night is lifted! Looking into the distance, we will see practically no substance - neither luminous nor dark. And this despite the fact that there will be countless stars and other celestial bodies.

This idea formed the basis for the curious star placement schemes that the Belgian cosmologist Charlier constructed at the beginning of the last century. Charlier borrowed their main feature from the 18th century astronomer Lambert. This feature is the hierarchical structure of the world. Celestial bodies form systems, the complexity of which increases with increasing size, and the average density of matter decreases. A world organized according to such rules is completely free not only from the prohibition of night darkness, but also from some other paradoxes that have arisen in cosmology.

At one time, Charlier's schemes seemed like a revelation. They seemed to contain a clue to the structure of the Universe. However, then the enthusiasm cooled. There was no direct evidence for Charlier's ideas. His systems remained just a guess. And yet, Charlier’s work was very useful. He showed that there are ways out of the dead ends of cosmology.

Meanwhile, the famous theory of relativity entered the scientific arena. But read about this in our next article.

Why is it dark at night? This seemingly simple childish question has interested both famous astronomy researchers and ordinary people.

There are an infinite number of stars in the sky and each of them is much larger than the Sun. The powerful starlight should have incinerated everything around, but, strangely enough, this does not happen and every night it becomes dark again.

Common hypotheses about darkness at night

Astronomer Johannes Kepler refuted the infinity of the Universe, erroneously claiming that the stars do not completely cover the sky. He believed that it becomes dark at night because of the empty places in the sky, where there are absolutely no stars.

In fact, numerous stars are simply distributed unevenly throughout the Universe and are located at different distances from the Earth. Therefore, we do not see all existing stars in the sky, but only those located closer to our planet.

There were other opinions. At night everyone saw a lot of brightest stars, but despite this, the night sky always remained dark. German astronomer Heinrich Olbers called this phenomenon a paradox and in 1823 put forward a theory about the absorption of stellar light flux by cosmic dust. And only about a hundred years ago, scientists proved that interstellar nebulae are clusters of galaxies, and not cosmic dust.

The Universe is infinite, and the sky is densely dotted with luminaries of different sizes. There are no empty or dark places in the sky, just many stars are infinitely far away and therefore invisible, some of them cannot be seen even with a very strong telescope.

Scientific explanation for darkness at night

The time of day changes for several reasons:

The Sun has a strong influence due to its close location to the Earth;


- The light of distant stars cannot reach our planet.

Earth Rotation

Now no one disputes the fact that the Earth has the shape of a huge ball and rotates around its axis at breakneck speed in the direction from west to east. This rotation is called diurnal; it is repeated with a period of one sidereal day.

The sun is the closest star to us

Of all the heavenly bodies, the Sun is located closest to the Earth. The sun's rays are a natural source of heat and light for several planets at the same time. When the time of day changes, the Sun illuminates and warms opposite corners of the globe.

Due to the constant rotation of the Earth, we create the illusion of the Sun moving across the sky. In reality, the Sun is always in one place, and our planet gradually turns towards it with its different sides. Each hemisphere in turn falls into shadow, the amount of light decreases and night falls.

Such distant stars

The stars do not disappear anywhere; at night and during the day they are directly above our heads. During the day they are not visible because they fall within the range of the hot solar radiation. At night, the Sun is covered by the shadow of the Earth, and the stars are very far away, their light simply does not have time to reach us.

Thus, even the celestial bodies visible to the human eye are located at a distance of billions of light years. For this reason, it becomes dark at night.

What will happen to the stars in billions of years?

If in the future the light of invisible stars finally reaches the Earth, the night will still not become brighter. By this time, the stars of our Universe will have time to go out, and the approach of other, more distant ones will require long time.


The Universe has no boundaries - some stars constantly fly towards the Earth, others go out. Therefore, even after billions of years, nothing will change; daylight will always be replaced by night darkness.

Earth is a planet that rotates around the Sun. It also moves around its own axis. These turns are complex and not fully explored. Despite the difficulties in determining rotations, scientists were able to establish why it is dark at night.

From Earth, the worlds appear to revolve around us. If you get up in the same place at the same time every day, you can see how the stars move across the sky, how the Sun passes across it. At such moments, it seems that our planet is the center of the universe.

Around the Sun

As already mentioned, the Earth always rotates around the brightest star of our solar system, and at the same time rotates around its own axis.

The planet completes a revolution around the star in three hundred sixty-five days and six hours. To make it more convenient to count dates, it was introduced calendar year, equal to 365 days. And once every four years, when twenty-four out of six hours have accumulated, another day is added. This year is called a “leap year”, and a new day is added to February.

As the Earth rotates around the star, the seasons change. Due to the fact that the planet has a certain angle of inclination - sixty-six and a half degrees, it moves in outer space. Due to the inclined position sunlight illuminates first one side and then the other of the planet. When it is day in the Western Hemisphere, it is night in the Eastern Hemisphere.

When the rays of the Sun fall at right angles on the planet, equinoxes are observed - day and night are the same length. This event happens twice a year: on the days of the spring (in March) and autumn (in September) equinox. The beginning of summer and winter is considered to be the dates when the Sun shines on the planet from the greatest height (in June and December).

The rotation of the earth's axis to the Sun

During winter solstice The earth's axis faces the sun with its southern end. And, accordingly, the sun's rays fall at southern latitudes. From this day on, on parallels south of the equator, the days become long and the nights short. Polar day begins to reign in the Antarctic Circle.

In all parts north of the equator, days are shorter than nights, and in the Arctic Circle there is deep night.

The polar circles are the boundaries of the polar day and night, which last from one to 178 days. During the entire polar night, the Sun sets below the horizon. During the polar day, the Sun shines and does not hide behind the horizon.

Spinning around yourself

The earth rotates around itself, making a full revolution every day. The planet rotates from east to west, so the Sun rises in the east and sets in the west.

The rotations of the planet around itself make it possible to understand why it is dark at night and the light hides behind the horizon. It is the appearance of the Sun and its descent that causes the change of day and night.

So why is it dark at night, and where is the light at this time? One part of the planet is constantly facing the Sun. And on that part of it where the sun's rays fall, daylight is observed. On the opposite ( dark side), to which the light does not reach, night is observed. During rotation, sunlight gradually penetrates into those areas that were dark until that moment, and from those where it was light, the Sun leaves. From Earth, this phenomenon is observed in the form of sunset and dawn.

The rotation of the planet around itself, during which it alternately exposes different areas to the sun's rays, counts the earth's day and changes day to night. At a time when the sun doesn't shine on western part planet, it illuminates the eastern one. Based on this, in the first part there will be night, and in the other - day. That's why it's dark at night.

Rotating around the galaxy

The Earth is located in the solar system, which is located in the Milky Way galaxy. It received its name for its special appearance: In the night sky it looks like spilled milk. In fact, white stripe is a collection of millions of stars.

The galaxy has a spiral shape. According to modern calculations, our Solar system is located closer to the edge of the galaxy, in one of its arms. It moves in a spiral around the center of the galaxy. According to calculations, a complete rotation around the center of the spiral Milky Way completes in approximately 225 million years.

Scientists about galactic rotation

Scientists believe that this rotation around the center of the galaxy must somehow affect our existence and all the planets of the solar system. However, there is no data yet on what specific events entail full revolutions. This is due to the small age of humanity, it is estimated at only tens of thousands of years, and scientists have been making serious observations of space and the phenomena occurring in it for only a few centuries.

Conclusion

The earth moves with ours solar system around the center of our galaxy. One complete rotation takes approximately 225 million years. At the same time, the Earth always rotates around our star. Moreover, during rotation the planet either moves away or approaches it. Because of this phenomenon, people observe the change of seasons. While rotating around a star, the Earth simultaneously rotates around its axis from west to east: because of this phenomenon, day gives way to night.