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Why do stars glow at night, but are not visible during the day? What are stars? Stars emit light because...

As you may recall from your school natural history course, stars are objects that have the ability to emit their own light. In contrast, other celestial bodies, such as planets, satellites, asteroids and comets, are visible in the sky due to reflected light; they do not have their own glow. The only exceptions are meteorites that fall into the Earth's atmosphere and fall due to the force of its gravity. They burn partially or completely during the fall due to friction with air particles, and glow due to this.

But why do stars glow? This is an interesting question, to which astronomers are ready to give a comprehensive answer.

History of the study of stars and their glow

For a long period of time, astronomers could not come to a consensus regarding the nature of starlight. This question has given rise to numerous disputes over many centuries. These disputes were not only of a scientific nature - at the dawn of civilization, people built numerous myths, legends and religious conjectures explaining the presence of stars in the sky and their glow. In the same way, legends and everyday explanations were created for other astronomical phenomena observed in the sky - comets, eclipses, the movements of luminaries.

Interesting fact: Some civilizations believed that the stars in the sky were the souls of the dead, others believed that these were the heads of nails with which the sky was nailed down. The Sun, on the other hand, was always considered separately; for thousands of years it was not classified as a star; it was too different in its appearance, observed from the surface of the Earth.

With the development of astronomy, the fallacy of such conclusions was revealed, and the stars began to be studied anew - like the Sun. Subsequently, it was possible to clarify that the Sun is also a star. Modern scientists classify the closest star to us as a red dwarf. However, the nature of the glow of the Sun and other stars gave rise to a lot of controversy until very recently.

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Theories explaining the glow of stars

In the 19th century, many scientific minds believed that a combustion process occurs on stars - exactly the same as in any earthly stove. But this theory was completely unjustified. It is difficult to imagine how much fuel a star must have in order for it to provide heat for millions of years. Therefore, this version does not deserve consideration. Chemists believed that exothermic reactions occur on stars, which provide a powerful release of large volumes of heat.

But physicists will not agree with this explanation, for the same reason as with the combustion process. The supply of reactants must be enormous to maintain the stars' luminosity and their ability to provide heat.

After Mendeleev's discoveries, the situation changed again, as the era of studying radiation and radioactive elements began. At that time, the heat and light generated by the stars and the Sun were unconditionally attributed to radioactive decay reactions; this version became generally accepted for decades. Subsequently, it was modified many times.

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Modern opinion of scientists about the causes of stellar glow

Modern scientists are completely convinced that nuclear fusion occurring in the cores of stars is capable of releasing the amount of energy that each star emits every second. This process is capable of providing glow and heat generation in huge volumes over billions of years.

Therefore, the theory is considered generally accepted. Energy from the interior passes into the gas shells of the star, from where it is radiated outward. There is an opinion in astronomer circles that it takes tens, hundreds of thousands of years to move energy from the depths of a star to its surface - this is by no means an instantaneous process. Therefore, a star can continue to shine for a long time even after synthesis in its depths ceases due to a lack of initial chemical elements.

Light from any star does not reach the surface of the Earth instantly either. Even from the Sun, the closest star to our planet, it takes about 8 minutes. The next closest star to our planet is Proxima Centauri. It takes more than four years for light to reach Earth.

The question of why stars glow is a childish one, but, nevertheless, it baffles a good half of adults who either forgot the school course in physics and astronomy or played truant a lot in childhood.

Explanation of star glow

Stars are essentially balls of gas, therefore, during their existence and the chemical processes occurring in them, they emit light. Unlike the moon, which simply reflects the light of the sun, stars, like our sun, glow themselves. If we talk about our sun, it is of average size, as is the age of the star. As a rule, those stars that visually appear larger in the sky are closer, those that are barely visible are further away. There are still millions of those that are not visible to the naked eye at all. People became acquainted with them when the first telescope was invented.

A star, although it is not alive, has its own life cycle, which is why at different stages it has a different glow. When her life's journey comes to an end, she gradually turns into a red dwarf. In this case, its light is, accordingly, reddish, pulses are possible, the light seems to flicker, like the glow of an incandescent lamp during sudden changes in voltage in the network. Certain parts of it either become crusty or explode again with renewed vigor, visually forming such blinking lights.

Another reason for the difference in cross-sections of stars lies in their spectrality. It's like the length and frequency of the light rays they emit. This depends on the chemical composition of the star, as well as its size.

All stars are also different in size. But what is meant here is not how they look to us when looking at the sky in the evening or at night, but their actual sizes, which are calculated with varying degrees of accuracy by astronomers.

It must be said that the stars glow not only at night, but also during the day. It’s just that the sun illuminates the atmosphere during the daytime, we see it consisting of many layers of clouds. At night, the sun illuminates the other side of the earth and where it is dark, the atmosphere becomes transparent. This is how we see what surrounds our planet - the stars, its companion, the Moon, sometimes even meteorites, comets, even another planet of the solar system - Venus. It appears to be a large star, but its glow, like that of the Moon, is due to the fact that it reflects sunlight. Venus is visible mainly in the early evening or at dawn.

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Why do the stars shine

INTRODUCTION

astronomy star universe

By the beginning of our century, the boundaries of the explored Universe had expanded so much that they included the Galaxy. Many, if not all, thought then that this huge star system was the entire Universe as a whole.

But in the 20s, new large telescopes were built, and completely unexpected horizons opened up for astronomers. It turned out that the world does not end outside the Galaxy. Billions of star systems, galaxies similar to ours and different from it, are scattered here and there throughout the vastness of the Universe.

Photographs of galaxies taken with the help of the largest telescopes amaze with the beauty and variety of shapes: these are powerful vortices of star clouds, and regular balls, while other star systems do not reveal any definite shapes at all, they are ragged and shapeless. All these types of galaxies - spiral, elliptical, irregular - named after their appearance in photographs, were discovered by the American astronomer E. Hubble in the 20-30s of our century.

If we could see our Galaxy from afar, it would appear to us completely different from the one in the schematic drawing. We would not see either a disk, a halo, or, of course, a crown. From great distances, only the brightest stars would be visible. And all of them, as it turned out, are collected in wide stripes that extend in arcs from the central region of the Galaxy. The brightest stars form its spiral pattern. Only this pattern would be visible from afar. Our Galaxy in a picture taken by an astronomer from some stellar world would look very similar to the Andromeda nebula.

Research in recent years has shown that many large spiral galaxies, like our Galaxy, have extended and massive invisible coronas. This is very important: after all, if so, then it means that in general almost the entire mass of the Universe (or, in any case, the overwhelming part of it) is a mysterious, invisible, but gravitating hidden mass

Many, and perhaps almost all, galaxies are collected in various groups, which are called groups, clusters and superclusters, depending on how many of them there are. A group may contain only three or four galaxies, but a supercluster may contain up to a thousand or even several tens of thousands. Our Galaxy, the Andromeda nebula and more than a thousand similar objects are included in the so-called Local Supercluster. It does not have a clearly defined shape.

Celestial bodies are in continuous movement and change. When and how exactly they occurred, science seeks to find out by studying celestial bodies and their systems. The branch of astronomy that deals with the origin and evolution of celestial bodies is called cosmogony.

Modern scientific cosmogonic hypotheses are the result of a physical, mathematical and philosophical generalization of numerous observational data. The cosmogonic hypotheses inherent in this era largely reflect the general level of development of natural science. The further development of science, which necessarily includes astronomical observations, confirms or refutes these hypotheses.

This paper addresses the following issues:

· The structure of the universe is presented, its main elements are characterized;

· The main methods for obtaining information about space objects are shown;

· The concept of a star, its characteristics and evolution is defined

· The main sources of stellar energy are presented

· A description is given of the star closest to our planet - the Sun

1. HISTORICAL DEVELOPMENT OF CONCEPTS ABOUT THE UNIVERSE

Even at the dawn of civilization, when the inquisitive human mind turned to transcendental heights, great philosophers conceived their idea of the Universe as something infinite.

The ancient Greek philosopher Anaximander (VI century BC) introduced the idea of a certain single infinity that did not have any usual observations and qualities. The elements were first thought of as semi-material, semi-divine, spiritualized substances. So, he said that the beginning and element of existence is the Infinite, being the first to give a name to the beginning. In addition, he spoke of the existence of eternal motion, in which the origin of the heavens occurs. The earth floats in the air, unsupported by anything, but remains in place due to equal distance from everywhere. Its shape is curved, rounded, similar to a section of a stone column. We walk along one of its planes, while the other is on the opposite side. The stars represent a circle of fire, separated from the world fire and surrounded by air. But in the air shell there are vents, some kind of tube-shaped, that is, narrow and long holes, downwards from which the stars are visible. As a result, when these vents are blocked, an eclipse occurs. The moon appears either full or at a loss, depending on the closing and opening of the holes. The solar circle is 27 times larger than the earth’s and 19 times larger than the lunar one, and the sun is the highest, and behind it the moon, and the circles of the fixed stars and planets are the lowest. Another Pythagorean Parmenides (VI-V centuries BC) argued that the Earth was spherical AD). Heraclides of Pontus (V-IV centuries BC) also claimed its rotation around its axis and conveyed to the Greeks the even more ancient idea of the Egyptians that the sun itself could serve as the center of rotation of some planets (Venus, Mercury).

The French philosopher and scientist, physicist, mathematician, physiologist Rene Descartes (1596-1650) created a theory about the evolutionary vortex model of the Universe based on heliocentralism. In his model, he considered celestial bodies and their systems in their development. For the 17th century his idea was unusually bold.

According to Descartes, all celestial bodies were formed as a result of vortex movements that occurred in the world's matter, which was homogeneous at the beginning. Exactly identical material particles, being in continuous movement and interaction, changed their shape and size, which led to the rich diversity of nature that we observed.

The great German scientist and philosopher Immanuel Kant (1724-1804) created the first universal concept of the evolving Universe, enriching the picture of its even structure and representing the Universe as infinite in a special sense.

He substantiated the possibilities and significant probability of the emergence of such a Universe solely under the influence of mechanical forces of attraction and repulsion and tried to find out the further fate of this Universe at all its scale levels - from the planetary system to the world of the nebula.

Einstein brought about a radical scientific revolution with his theory of relativity. Einstein's special or partial theory of relativity was the result of a generalization of Galilean mechanics and Maxwell Lorentz's electrodynamics.

It describes the laws of all physical processes at speeds close to the speed of light. For the first time, fundamentally new cosmological consequences of the general theory of relativity were revealed by the outstanding Soviet mathematician and theoretical physicist Alexander Friedman (1888-1925). Having performed in 1922-24. he criticized Einstein's conclusions that the Universe is finite and shaped like a four-dimensional cylinder. Einstein made his conclusion based on the assumption that the Universe is stationary, but Friedman showed the groundlessness of his initial postulate.

Friedman gave two models of the Universe. Soon these models found surprisingly accurate confirmation in direct observations of the movements of distant galaxies due to the “red shift” effect in their spectra. In 1929, Hubble discovered a remarkable pattern that was called "Hubble's Law" or "Redshift Law": lines of galaxies redshifted, with the shift increasing the further away the galaxy is.

2. OBSERVATIONAL ASTRONOMY TOOLS

Telescopes

The main astronomical instrument is the telescope. A telescope with a concave mirror lens is called a reflector, and a telescope with a lens lens is called a refractor.

The purpose of a telescope is to collect more light from celestial sources and increase the viewing angle from which a celestial object is seen.

The amount of light that enters the telescope from the observed object is proportional to the area of the lens. The larger the telescope lens, the fainter luminous objects can be seen through it.

The scale of the image produced by the telescope lens is proportional to the focal length of the lens, i.e., the distance from the lens collecting light to the plane where the image of the luminary is obtained. The image of a celestial object can be photographed or viewed through an eyepiece.

A telescope increases the apparent angular sizes of the Sun, Moon, planets and details on them, as well as the angular distances between stars, but stars, even in a very powerful telescope, due to their enormous distance, are visible only as luminous points.

In a refractor, rays passing through the lens are refracted, forming an image of the object in the focal plane . In a reflector, rays from a concave mirror are reflected and then also collected in the focal plane. When making a telescope lens, they strive to minimize all the distortions that inevitably occur in the image of objects. A simple lens greatly distorts and colors the edges of the image. To reduce these disadvantages, the lens is made from several lenses with different surface curvatures and from different types of glass. To reduce distortion, the surfaces of a concave glass mirror are given not a spherical shape, but a slightly different (parabolic) shape.

Soviet optician D.D. Maksutov developed a telescope system called the meniscus. It combines the advantages of a refractor and a reflector. One of the school telescope models is based on this system. There are other telescopic systems.

The telescope produces an inverted image, but this has no significance when observing space objects.

When observing through a telescope, magnifications exceeding 500 times are rarely used. The reason for this is air currents that cause image distortions, which are more noticeable the higher the telescope magnification.

The largest refractor has a lens with a diameter of about 1 m. The world's largest reflector with a concave mirror diameter of 6 m was made in the USSR and installed in the Caucasus mountains. It allows you to photograph stars 107 times fainter than those visible to the naked eye.

Spectral certificate

Until the middle of the 20th century. We owe our knowledge of the Universe almost exclusively to mysterious rays of light. A light wave, like any other wave, is characterized by frequency x and wavelength l. There is a simple relationship between these physical parameters:

where c is the speed of light in vacuum (emptiness). And the energy of photons is proportional to the frequency of radiation.

In nature, light waves propagate best in the vastness of the Universe, since there is the least amount of interference on their path. And man, armed with optical instruments, learned to read mysterious light writings. Using a special instrument - a spectroscope, adapted to a telescope, astronomers began to determine the temperature, brightness and size of stars; their speeds, chemical composition and even processes occurring in the depths of distant stars.

Isaac Newton discovered that white sunlight consists of a mixture of rays of all the colors of the rainbow. When passing from air to glass, color rays are refracted to different degrees. Therefore, if a triangular prism is placed in the path of a narrow solar beam, then after the beam leaves the prism, a rainbow stripe appears on the screen, which is called a spectrum.

The spectrum contains the most important information about the celestial body emitting light. Without any exaggeration, we can say that astrophysics owes its remarkable successes primarily to spectral analysis. Spectral analysis is nowadays the main method for studying the physical nature of celestial bodies.

Each gas, each chemical element produces its own, unique lines in the spectrum. They may be similar in color, but they necessarily differ from one another in their location in the spectral strip. In a word, the spectrum of a chemical element is its unique “passport”. And an experienced spectroscopist need only look at a set of colored lines to determine which substance is emitting light. Consequently, to determine the chemical composition of a luminous body, there is no need to pick it up and subject it to direct laboratory research. Distances here, even cosmic distances, are also not a hindrance. It is only important that the body under study be in a red-hot state - it glows brightly and produces a spectrum. When studying the spectrum of the Sun or another star, an astronomer deals with dark lines, the so-called absorption lines. The absorption lines exactly coincide with the emission lines of a given gas. It is thanks to this that the chemical composition of the Sun and stars can be studied from absorption spectra. By measuring the energy emitted or absorbed in individual spectral lines, it is possible to conduct a quantitative chemical analysis of the celestial bodies, that is, to learn about the percentage content of various chemical elements. Thus, it was established that the atmospheres of stars are dominated by hydrogen and helium.

A very important characteristic of a star is its temperature. To a first approximation, the temperature of a celestial body can be judged by its color. Spectroscopy makes it possible to determine the surface temperature of stars with very high accuracy.

The temperature of the surface layer of most stars ranges from 3000 to 25000 K.

The possibilities of spectral analysis are almost inexhaustible! He convincingly showed that the chemical composition of the Earth, the Sun and the stars is the same. True, on individual celestial bodies there may be more or less of some chemical elements, but the presence of any special “unearthly substance” has not been discovered anywhere. The similarity of the chemical composition of celestial bodies serves as an important confirmation of the material unity of the Universe.

Astrophysics, a large department of modern astronomy, studies the physical properties and chemical composition of celestial bodies and the interstellar medium. She develops theories of the structure of celestial bodies and the processes occurring in them. One of the most important tasks facing astrophysics today is to clarify the internal structure of the Sun and stars and the sources of their energy, and to establish the process of their origin and development. And we owe all the rich information coming to us from the depths of the Universe to the messengers of distant worlds - rays of light.

Anyone who has observed the starry sky knows that constellations do not change their shape. Ursa Major and Ursa Minor look like a ladle, the constellation Cygnus has the shape of a cross, and the zodiac constellation Leo resembles a trapezoid. However, the impression that the stars are motionless is deceptive. It is created only because the heavenly lights are very far from us, and even after many hundreds of years the human eye is not able to notice their movement. Currently, astronomers measure the proper motion of stars from photographs of the starry sky taken at intervals of 20, 30 or more years.

The proper motion of stars is the angle at which a star moves across the sky in one year. If the distance to this star is also measured, then it is possible to calculate its own speed, i.e. that part of the speed of the celestial body that is perpendicular to the line of sight, namely, the “observer-star” direction. But in order to obtain the full speed of the star in space, it is also necessary to know the speed directed along the line of sight - towards or away from the observer.

Fig. 1 Determination of the spatial velocity of a star at a known distance to it

The radial velocity of a star can be determined by the location of absorption lines in its spectrum. As is known, all lines in the spectrum of a moving light source shift in proportion to the speed of its movement. For a star flying towards us, the light waves are shortened and the spectral lines shift towards the violet end of the spectrum. As a star moves away from us, the light waves lengthen and the lines shift toward the red end of the spectrum. In this way, astronomers find the speed of motion of the star along the line of sight. And when both velocities (intrinsic and radial) are known, it is not difficult to use the Pythagorean theorem to calculate the total spatial velocity of the star relative to the Sun.

It turned out that the speeds of stars are different and, as a rule, amount to several tens of kilometers per second.

By studying the proper movements of stars, astronomers were able to imagine the appearance of the starry sky (constellations) in the distant past and in the distant future. The famous “bucket” of the Big Dipper in 100 thousand years will turn, for example, into an “iron with a broken handle.”

Radio waves and radio telescopes

Until recently, celestial bodies were studied almost exclusively in the visible rays of the spectrum. But in nature there are also invisible electromagnetic radiations. They are not perceived even with the most powerful optical telescopes, although their range is many times wider than the visible region of the spectrum. So, beyond the violet end of the spectrum are invisible ultraviolet rays, which actively affect the photographic plate - causing it to darken. Behind them are X-rays and, finally, gamma rays with the shortest wavelength.

To capture radio radiation coming to us from space, special radiophysical instruments are used - radio telescopes. The operating principle of a radio telescope is the same as an optical telescope: it collects electromagnetic energy. Only instead of lenses or mirrors, radio telescopes use antennas. Very often, a radio telescope antenna is constructed in the form of a huge parabolic bowl, sometimes solid and sometimes lattice. Its reflective metal surface concentrates the radio emission of the observed object on a small receiving antenna-feeder, which is placed at the focus of the paraboloid. As a result, weak alternating currents arise in the irradiator. Electrical currents are transmitted through waveguides to a very sensitive radio receiver tuned to the operating wavelength of the radio telescope. Here they are amplified, and by connecting a loudspeaker to the receiver, one could listen to the “voices of the stars.” But the voices of the stars are devoid of any musicality. These are not at all “cosmic melodies” that enchant the ear, but a crackling hiss or a piercing whistle... Therefore, a special recording device is usually attached to the radio telescope receiver. And now, on the moving tape, the recorder draws a curve of the intensity of the input radio signal of a certain wavelength. Consequently, radio astronomers do not “hear” the rustling of stars, but “see” it on graphed paper.

As you know, with an optical telescope we immediately observe everything that falls into its field of view.

With a radio telescope the situation is more complicated. There is only one receiving element (feeder), so the image is built line by line - by sequentially passing a radio source through the antenna beam, that is, similar to how on a television screen.

Wine's Law

Wine's Law- dependence that determines the wavelength when energy is emitted by an absolutely black body. It was developed by German physicist and Nobel laureate Wilhelm Wien in 1893.

Wien's Law: The wavelength at which a black body emits the greatest amount of energy is inversely proportional to the temperature of that body.

A completely black body is a surface that completely absorbs radiation incident on it. The concept of an absolutely black body is purely theoretical: in reality, objects with such an ideal surface that completely absorbs all waves do not exist.

3. MODERN CONCEPTS ABOUT THE STRUCTURE, BASIC ELEMENTS OF THE VISIBLE UNIVERSE AND THEIR SYSTEMATIZATION

If we describe the structure of the Universe, as it appears to scientists now, we will get the following hierarchical ladder. There are planets - celestial bodies revolving in orbit around a star or its remnants, massive enough to become rounded under the influence of their own gravity, but not massive enough to initiate a thermonuclear reaction, which are “tied” to a particular star, that is, located in its zone gravitational influence. Thus, the Earth and several other planets with their satellites are in the zone of gravitational influence of a star called the Sun, moving in their own orbits around it and thereby forming the Solar System. Similar star systems, located nearby in huge numbers, form a galaxy - a complex system with its own center. By the way, regarding the center of galaxies, there is no consensus yet on what they are - it has been suggested that there are black holes in the center of galaxies.

Galaxies, in turn, form a kind of chain, creating a kind of grid. The cells of this grid are created from chains of galaxies and central “voids”, which are either completely devoid of galaxies or have a very small number of them. The main part of the Universe is occupied by vacuum, which, however, does not mean the absolute emptiness of this space: individual atoms are also present in the vacuum, photons are present (relict radiation), and particles and antiparticles also appear as a result of quantum phenomena. The visible part of the Universe, that is, that part of it that is accessible to the study of mankind, is characterized by homogeneity and constancy in the sense that, as is commonly believed, the same laws operate in this part. Whether the situation is also the same in other parts of the Universe cannot be determined.

In addition to planets and stars, the elements of the Universe are such celestial bodies as comets, asteroids and meteorites.

A comet is a small celestial body revolving around the Sun along a conical section with a very extended orbit. As the comet approaches the Sun, it forms a coma and sometimes a tail of gas and dust.

Conventionally, a comet can be divided into three parts - the nucleus, the coma, and the tail. Everything in comets is absolutely cold, and their glow is only the reflection of sunlight by dust and the glow of gas ionized by ultraviolet light.

The core is the heaviest part of this celestial body. The bulk of the comet is concentrated in it. The composition of the comet's nucleus is quite difficult to accurately study, since at a distance accessible to a telescope, it is constantly surrounded by a gas mantle. In this regard, the theory of the American astronomer Whipple was adopted as the basis for the theory about the composition of the comet's nucleus.

According to his theory, the comet's nucleus is a mixture of frozen gases mixed with various dust. Therefore, when a comet approaches the Sun and heats up, the gases begin to “melt”, forming a tail.

The tail of a comet is its most expressive part. It is formed by a comet as it approaches the Sun. The tail is a luminous strip that stretches from the core in the direction opposite to the Sun, “blown” by the solar wind.

Coma is a cup-shaped, light, foggy shell surrounding the core, consisting of gases and dust. Typically extends from 100 thousand to 1.4 million kilometers from the core. Light pressure can deform the coma, stretching it in the anti-solar direction. The coma, together with the nucleus, makes up the head of the comet.

Asteroids are celestial bodies that have a mostly irregular, rock-like shape and range in size from a few meters to a thousand kilometers. Asteroids, like meteorites, are made of metals (mainly iron and nickel) and rocks. In Latin, the word asteroid means “like a star.” Asteroids received this name for their resemblance to stars when observed using not very powerful telescopes.

Asteroids can collide with each other, with satellites and with large planets. As a result of the collision of asteroids, smaller celestial bodies are formed - meteorites. When they collide with a planet or satellite, asteroids leave traces in the form of huge craters many kilometers long.

The surface of all asteroids, without exception, is very cold, since they themselves are like large rocks and do not generate heat, and are located at a considerable distance from the sun. Even if the asteroid is heated by the Sun, it gives off heat quickly enough.

Astronomers have two most popular hypotheses regarding the origin of asteroids. According to one of them, they are fragments of once existing planets that were destroyed as a result of a collision or explosion. According to another version, asteroids were formed from the remains of the substance from which the planets of the solar system were formed.

Meteorites- small fragments of celestial bodies, consisting mainly of stone and iron, falling to the surface of the Earth from interplanetary space. For astronomers, meteorites are a real treasure: it is not often that they are able to thoroughly examine a piece of space in laboratory conditions. Most experts consider meteorites to be fragments of asteroids that are formed during the collision of cosmic bodies.

4. THEORY OF STARS

A star is a massive ball of gas that emits light and is held by the forces of its own gravity and internal pressure, in the depths of which thermonuclear fusion reactions occur (or have occurred previously).

Main characteristics of stars:

Luminosity

Luminosity is determined if the apparent magnitude and distance to the star are known. While astronomy has quite reliable methods for determining the apparent magnitude, the distance to stars is not so easy to determine. For relatively close stars, the distance is determined by the trigonometric method, known since the beginning of the last century, which consists in measuring negligible angular displacements of stars when they are observed from different points of the earth's orbit, that is, at different times of the year. This method has quite high accuracy and is quite reliable. However, for most other more distant stars it is no longer suitable: the shifts in the positions of the stars must be measured too small - less than one hundredth of an arcsecond. Other methods come to the rescue, much less accurate, but nevertheless quite reliable. In a number of cases, the absolute magnitude of stars can be determined directly, without measuring the distance to them, from some observed features of their radiation.

Stars vary greatly in their luminosity. There are white and blue supergiant stars (though there are relatively few of them), the luminosity of which exceeds the luminosity of the Sun by tens and even hundreds of thousands of times. But the majority of stars are “dwarfs”, whose luminosity is much less than the Sun, often thousands of times. The luminosity characteristic is the so-called “absolute magnitude” of the star. The apparent magnitude of a star depends, on the one hand, on its luminosity and color, on the other, on the distance to it. Stars with high luminosity have negative absolute values, for example -4, -6. Low luminosity stars are characterized by large positive values, for example +8, +10.

Chemical composition of stars

The chemical composition of the outer layers of the star, from where their radiation “directly” comes to us, is characterized by a complete predominance of hydrogen. Helium is in second place, and the abundance of other elements is relatively small. For about every 10,000 hydrogen atoms, there are a thousand helium atoms, about ten oxygen atoms, slightly less carbon and nitrogen, and just one iron atom. The abundance of other elements is completely negligible.

We can say that the outer layers of stars are giant hydrogen-helium plasmas with a small admixture of heavier elements.

Although the chemical composition of stars is, to a first approximation, the same, there are still stars that show certain features in this regard. For example, there is a star with an anomalously high carbon content, or there are objects with an abnormally high content of rare earths. If the vast majority of stars have a completely negligible abundance of lithium (approximately 10 11 from hydrogen), then occasionally there are “uniques” where this rare element is quite abundant.

Spectra of stars

Studying the spectra of stars provides exceptionally rich information. The so-called Harvard spectral classification has now been adopted. It has ten classes, designated in Latin letters: O, B, A, F, G, K, M. The existing system for classifying stellar spectra is so accurate that it allows one to determine the spectrum with an accuracy of one tenth of the class. For example, part of the sequence of stellar spectra between classes B and A is designated as B0, B1 ... B9, A0 and so on. The spectrum of stars, to a first approximation, is similar to the spectrum of a radiating “black” body with a certain temperature T. These temperatures smoothly change from 40-50 thousand kelvins for stars of spectral class O to 3000 kelvins for stars of spectral class M. In accordance with this, the main part of the radiation of stars spectral classes O and B fall in the ultraviolet part of the spectrum, inaccessible for observation from the surface of the earth.

Another characteristic feature of stellar spectra is the presence of a huge number of absorption lines belonging to various elements. Fine analysis of these lines provided particularly valuable information about the nature of the outer layers of stars. The differences in the spectra are primarily explained by differences in the temperatures of the outer layers of the star. For this reason, the ionization and excitation states of different elements in the outer layers of stars differ dramatically, leading to strong differences in the spectra.

Temperature

Temperature determines the color of a star and its spectrum. So, for example, if the surface temperature of the layers of stars is 3-4 thousand. K., then its color is reddish, 6-7 thousand K. is yellowish. Very hot stars with temperatures above 10-12 thousand K. have a white or bluish color. In astronomy, there are completely objective methods for measuring the color of stars. The latter is determined by the so-called “color index”, equal to the difference between the photographic and visual values. Each color index value corresponds to a certain type of spectrum.

For cool red stars, the spectra are characterized by absorption lines of neutral metal atoms and bands of some simple compounds (for example, CN, SP, H20, etc.). As the surface temperature increases, molecular bands disappear in the spectra of stars, many lines of neutral atoms, as well as lines of neutral helium, weaken. The appearance of the spectrum itself is changing radically. For example, in hot stars with surface temperatures exceeding 20 thousand K, predominantly lines of neutral and ionized helium are observed, and the continuous spectrum is very intense in the ultraviolet part. Stars with a surface temperature of about 10 thousand K have the most intense lines of hydrogen, while stars with a temperature of about 6 thousand K have lines of ionized calcium, located on the border of the visible and ultraviolet parts of the spectrum.

Mass of stars

Astronomy did not have and does not currently have a method for directly and independently determining the mass (that is, not included in multiple systems) of an isolated star. And this is a very serious shortcoming of our science about the Universe. If such a method existed, the progress of our knowledge would be much more rapid. The masses of stars vary within relatively narrow limits. There are very few stars whose masses are 10 times greater or less than the solar mass. In such a situation, astronomers tacitly accept that stars with the same luminosity and color have the same masses. They are defined only for binary systems. The statement that a single star with the same luminosity and color has the same mass as its “sister” in a binary system should always be taken with some caution.

It is believed that objects with masses less than 0.02 M are no longer stars. They have no internal sources of energy, and their luminosity is close to zero. Usually these objects are classified as planets. The largest directly measured masses do not exceed 60 M.

CLASSIFICATION OF STARS

Classifications of stars began to be built immediately after their spectra began to be obtained. At the beginning of the 20th century, Hertzschprung and Russell plotted various stars on a diagram, and it turned out that most of them were grouped along a narrow curve. Hertzsprung diagram--shows the relationship between absolute magnitude, luminosity, spectral type and surface temperature of the star. The stars in this diagram are not located randomly, but form clearly visible areas.

The diagram makes it possible to find the absolute value by spectral class. Especially for spectral classes O--F. For later classes this is complicated by the need to choose between a giant and a dwarf. However, certain differences in the intensity of some lines allow us to confidently make this choice.

About 90% of stars are on the main sequence. Their luminosity is due to thermonuclear reactions converting hydrogen into helium. There are also several branches of evolved giant stars in which helium and heavier elements burn. At the bottom left of the diagram are fully evolved white dwarfs.

TYPES OF STARS

Giants-- a type of star with a significantly larger radius and higher luminosity than main sequence stars having the same surface temperature. Typically, giant stars have radii from 10 to 100 solar radii and luminosities from 10 to 1000 solar luminosities. Stars with a luminosity greater than that of the giants are called supergiants and hypergiants. Hot and bright main sequence stars can also be classified as white giants. In addition, due to their large radius and high luminosity, the giants lie above the main sequence.

Dwarfs- a type of small stars from 1 to 0.01 radius. The Sun and low luminosities from 1 to 10-4 the luminosity of the Sun with a mass from 1 to 0.1 solar mass.

· White dwarf- evolved stars with a mass not exceeding 1.4 solar masses, deprived of their own sources of thermonuclear energy. The diameter of such stars can be hundreds of times smaller than that of the Sun, and therefore the density can be 1,000,000 times greater than the density of water.

· Red dwarf- a small and relatively cool main sequence star with a spectral class of M or upper K. They are quite different from other stars. The diameter and mass of red dwarfs does not exceed a third of the solar mass (the lower limit of mass is 0.08 solar, followed by brown dwarfs).

· Brown dwarf-- substellar objects with masses in the range of 5-75 Jupiter masses (and a diameter approximately equal to the diameter of Jupiter), in the depths of which, unlike main sequence stars, no thermonuclear fusion reaction occurs with the conversion of hydrogen into helium.

· Subbrown dwarfs or brown subdwarfs-- cold formations with masses below the limit of brown dwarfs. They are generally considered to be planets.

· Black dwarf- white dwarfs that have cooled and, as a result, do not emit in the visible range. Represents the final stage of the evolution of white dwarfs. The masses of black dwarfs, like the masses of white dwarfs, are limited above 1.4 solar masses.

Neutron star- stellar formations with masses of the order of 1.5 solar and sizes noticeably smaller than white dwarfs, about 10-20 km in diameter. The density of such stars can reach 1000,000,000,000 densities of water. And the magnetic field is the same number of times greater than the Earth’s magnetic field. Such stars consist mainly of neutrons, tightly compressed by gravitational forces. Often such stars are pulsars.

New star- stars whose luminosity suddenly increases 10,000 times. The nova is a binary system consisting of a white dwarf and a companion star located on the main sequence. In such systems, gas from the star gradually flows to the white dwarf and periodically explodes there, causing a burst of luminosity.

Supernova- this is a star that ends its evolution in a catastrophic explosive process. The flare in this case can be several orders of magnitude larger than in the case of a nova. Such a powerful explosion is a consequence of the processes occurring in the star at the last stage of evolution.

Double star- these are two gravitationally bound stars revolving around a common center of mass. Sometimes there are systems of three or more stars, in this general case the system is called a multiple star. In cases where such a star system is not too far from the Earth, individual stars can be distinguished through a telescope. If the distance is significant, then it is possible to understand that astronomers can see a double star only by indirect signs - fluctuations in brightness caused by periodic eclipses of one star by another and some others.

Pulsars- these are neutron stars in which the magnetic field is inclined to the rotation axis and, while rotating, they cause modulation of the radiation that comes to Earth.

The first pulsar was discovered using the Mallard Radio Astronomy Observatory radio telescope. Cambridge University. The discovery was made by graduate student Jocelyn Bell in June 1967 at a wavelength of 3.5 m, that is, 85.7 MHz. This pulsar is called PSR J1921+2153. Observations of the pulsar were kept secret for several months, and it was then named LGM-1, which means “little green men.” The reason for this was radio pulses that reached the Earth at regular intervals, and therefore it was assumed that these radio pulses were of artificial origin.

Jocelyn Bell was in Hewish's group, they found 3 more sources of similar signals, after which no one doubted that the signals were not of artificial origin. By the end of 1968, 58 pulsars had already been discovered. And in 2008, 1,790 radio pulsars were already known. The closest pulsar to our solar system is 390 light years away.

Quasars are brilliant objects that emit the most significant amounts of energy found in the Universe. Being at a colossal distance from the Earth, they demonstrate greater brightness than cosmic bodies located 1000 times closer. According to the modern definition, a quasar is the active nucleus of a galaxy, where processes occur that release a huge amount of energy. The term itself means “star-like radio source.” The first quasar was noticed by American astronomers A. Sandage and T. Matthews, who were observing stars at a California observatory. In 1963, M. Schmidt, using a reflector telescope that collected electromagnetic radiation at one point, discovered a deviation in the spectrum of the observed object towards the red, which determined that its source was moving away from our system. Subsequent studies showed that the celestial body, recorded as 3C 273, is located at a distance of 3 billion light years. years and is receding at a tremendous speed - 240,000 km/s. Moscow scientists Sharov and Efremov studied the available early photographs of the object and found that it repeatedly changed its brightness. Irregular changes in brightness intensity suggest a small source size.

5. ENERGY SOURCES OF STARS

Over the course of a hundred years after R. Mayer formulated the law of conservation of energy in 1842, many hypotheses were expressed about the nature of the energy sources of stars, in particular, a hypothesis was proposed about the fall of meteoroids on a star, the radioactive decay of elements, and the annihilation of protons and electrons. Only gravitational compression and thermonuclear fusion are of real importance.

Thermonuclear fusion in the interior of stars

By 1939, it was established that the source of stellar energy was thermonuclear fusion occurring in the bowels of stars. Most stars radiate because in their core four protons combine through a series of intermediate steps into one alpha particle. This transformation can occur in two main ways, called the proton-proton or p-p cycle and the carbon-nitrogen or CN cycle. In low-mass stars, energy release is mainly provided by the first cycle, in heavy stars - by the second. The supply of nuclear energy in a star is finite and is constantly spent on radiation. The process of thermonuclear fusion, which releases energy and changes the composition of the star's matter, in combination with gravity, which tends to compress the star and also releases energy, and radiation from the surface, which carries away the released energy, are the main driving forces of stellar evolution.

Hans Albrecht Bethe is an American astrophysicist who won the Nobel Prize in Physics in 1967. The main works are devoted to nuclear physics and astrophysics. It was he who discovered the proton-proton cycle of thermonuclear reactions (1938) and proposed a six-stage carbon-nitrogen cycle to explain the process of thermonuclear reactions in massive stars, for which he received the Nobel Prize in Physics for “contributions to the theory of nuclear reactions, especially for the discoveries relating to the energy sources of stars."

Gravitational compression

Gravitational compression is an internal process of a star due to which its internal energy is released.

Suppose that at some point in time, due to the cooling of the star, the temperature in its center will decrease slightly. The pressure in the center will also decrease and will no longer compensate for the weight of the overlying layers. Gravity forces will begin to compress the star. In this case, the potential energy of the system will decrease (since the potential energy is negative, its module will increase), while the internal energy, and therefore the temperature inside the star, will increase. But only half of the released potential energy will be spent on increasing the temperature, the other half will be used to maintain the radiation of the star.

6. EVOLUTION OF STARS

Stellar evolution in astronomy is the sequence of changes that a star undergoes during its life, that is, over millions or billions of years while it emits light and heat. Over such enormous periods of time, the changes are quite significant.

The main phases in the evolution of a star are its birth (star formation), a long period of (usually stable) existence of the star as an integral system in hydrodynamic and thermal equilibrium, and, finally, the period of its “death,” i.e. an irreversible imbalance that leads to the destruction of a star or its catastrophic contraction. The course of a star's evolution depends on its mass and initial chemical composition, which, in turn, depends on the time of formation of the star and its position in the Galaxy at the time of formation. The greater the mass of a star, the faster its evolution and the shorter its “life.”

A star begins its life as a cold, rarefied cloud of interstellar gas, compressed under its own gravity and gradually taking the shape of a ball. When compressed, gravitational energy turns into heat, and the temperature of the object increases. When the temperature in the center reaches 15-20 million K, thermonuclear reactions begin and compression stops. The object becomes a full-fledged star.

After a certain time - from a million to tens of billions of years (depending on the initial mass) - the star depletes the hydrogen resources of the core. In large and hot stars this happens much faster than in small and cooler ones. Depletion of the hydrogen supply leads to the stopping of thermonuclear reactions.

Without the pressure that arose during these reactions and balanced the internal gravity in the body of the star, the star begins to contract again, as it previously did during its formation. Temperature and pressure rise again, but, unlike the protostar stage, to a much higher level. The collapse continues until thermonuclear reactions involving helium begin at a temperature of approximately 100 million K.

The thermonuclear “burning” of matter, resumed at a new level, causes a monstrous expansion of the star. The star "swells", becoming very "loose", and its size increases by approximately 100 times. So the star becomes a red giant, and the helium burning phase lasts about several million years. Almost all red giants are variable stars.

After the cessation of thermonuclear reactions in their core, they, gradually cooling, will continue to weakly emit in the infrared and microwave ranges of the electromagnetic spectrum.

SUN

The Sun is the only star in the Solar System; all the planets of the system, as well as their satellites and other objects, including cosmic dust, move around it.

Characteristics of the Sun

· Mass of the Sun: 2,1030 kg (332,946 Earth masses)

Diameter: 1,392,000 km

· Radius: 696,000 km

Average density: 1,400 kg/m3

Axis tilt: 7.25° (relative to the ecliptic plane)

Surface temperature: 5,780 K

Temperature at the center of the Sun: 15 million degrees

Spectral class: G2 V

Average distance from Earth: 150 million km

· Age: about 5 billion years

Rotation period: 25,380 days

Luminosity: 3.86 1026 W

· Apparent magnitude: 26.75m

Structure of the sun

According to the spectral classification, the star is a “yellow dwarf” type; according to rough calculations, its age is just over 4.5 billion years, it is in the middle of its life cycle. The sun, consisting of 92% hydrogen and 7% helium, has a very complex structure. At its center there is a core with a radius of approximately 150,000-175,000 km, which is up to 25% of the total radius of the star; at its center the temperature approaches 14,000,000 K. The core rotates around its axis at high speed, and this speed significantly exceeds indicators of the outer shells of the star. Here, the reaction of helium formation from four protons occurs, resulting in a large amount of energy passing through all layers and emitted from the photosphere in the form of kinetic energy and light. Above the core there is a zone of radiative transfer, where temperatures are in the range of 2-7 million K. This is followed by a convective zone approximately 200,000 km thick, where there is no longer re-radiation for energy transfer, but plasma mixing. At the surface of the layer, the temperature is approximately 5800 K. The atmosphere of the Sun consists of the photosphere, which forms the visible surface of the star, the chromosphere, which is about 2000 km thick, and the corona, the last outer shell of the sun, the temperature of which is in the range of 1,000,000-20,000,000 K. From the outer part The corona causes the release of ionized particles called solar wind.

Magnetic fields play an important role in the occurrence of phenomena occurring on the Sun. The matter on the Sun is everywhere a magnetized plasma. Sometimes in certain areas the magnetic field strength increases quickly and strongly. This process is accompanied by the emergence of a whole complex of solar activity phenomena in various layers of the solar atmosphere. These include faculae and spots in the photosphere, flocculi in the chromosphere, and prominences in the corona. The most remarkable phenomenon, covering all layers of the solar atmosphere and originating in the chromosphere, are solar flares.

During observations, scientists found that the Sun is a powerful source of radio emission. Radio waves penetrate into interplanetary space, which are emitted by the chromosphere (centimeter waves) and the corona (decimeter and meter waves).

Radio emission from the Sun has two components - constant and variable (bursts, “noise storms”). During strong solar flares, radio emission from the Sun increases thousands and even millions of times compared to radio emission from the quiet Sun. This radio emission is non-thermal in nature.

X-rays come mainly from the upper layers of the chromosphere and corona. The radiation is especially strong during the years of maximum solar activity.

The sun emits not only light, heat and all other types of electromagnetic radiation. It is also a source of a constant flow of particles - corpuscles. Neutrinos, electrons, protons, alpha particles, and heavier atomic nuclei all together make up the corpuscular radiation of the Sun. A significant part of this radiation is a more or less continuous outflow of plasma - the solar wind, which is a continuation of the outer layers of the solar atmosphere - the solar corona. Against the background of this constantly blowing plasma wind, individual regions on the Sun are sources of more directed, enhanced, so-called corpuscular flows. Most likely, they are associated with special regions of the solar corona - coronary holes, and also, possibly, with long-lived active regions on the Sun. Finally, the most powerful short-term fluxes of particles, mainly electrons and protons, are associated with solar flares. As a result of the most powerful flares, particles can acquire speeds that are a noticeable fraction of the speed of light. Particles with such high energies are called solar cosmic rays.

Solar corpuscular radiation has a strong influence on the Earth, and primarily on the upper layers of its atmosphere and magnetic field, causing many interesting geophysical phenomena.

Evolution of the sun

It is believed that the Sun was formed approximately 4.5 billion years ago, when the rapid compression under the influence of gravity of a cloud of molecular hydrogen led to the formation of a type 1 star of the T Tauri population in our region of the Galaxy.

A star as massive as the Sun should exist on the main sequence for a total of about 10 billion years. Thus, the Sun is now approximately in the middle of its life cycle. At the present stage, thermonuclear reactions are taking place in the solar core, converting hydrogen into helium. Every second in the Sun's core, about 4 million tons of matter is converted into radiant energy, resulting in the generation of solar radiation and a flux of solar neutrinos.

When the Sun reaches an age of approximately 7.5 - 8 billion years (that is, in 4-5 billion years), the star will turn into a red giant, its outer shells will expand and reach the Earth's orbit, possibly pushing the planet further away. Under the influence of high temperatures, life as we understand it today will simply become impossible. The Sun will spend the final cycle of its life as a white dwarf.

CONCLUSION

From this work the following conclusions can be drawn:

· Basic elements of the structure of the Universe: galaxies, stars, planets

Galaxies are systems of billions of stars orbiting the center of the galaxy and connected by mutual gravity and common origin,

Planets are bodies that do not emit energy and have a complex internal structure.

The most common celestial bodies in the observable Universe are stars.

According to modern concepts, a star is a gas-plasma object in which thermonuclear fusion occurs at temperatures above 10 million degrees K.

· The main methods for studying the visible Universe are telescopes and radio telescopes, spectral readings and radio waves;

· The main concepts describing stars are:

Stellar magnitude, which characterizes not the size of the star, but its brilliance, that is, the illumination that the star creates on Earth;

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OTHER

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