Solar atmosphere, photosphere, chromosphere and corona of a star. The main layers in the solar atmosphere What is the visible layer of the solar atmosphere called?

Structure of the Sun

1 – core, 2 – radiative equilibrium zone, 3 – convective zone, 4 – photosphere, 5 – chromosphere, 6 – corona, 7 – spots, 8 – granulation, 9 – prominence

Internal structure of the Sun. Core

The central part of the Sun with a radius of about 150,000 km (0.2 - 0.25 solar radii), in which thermonuclear reactions occur, is called the solar core.

The density of the substance in the core is approximately 150,000 kg/m³ (150 times higher than the density of water and ~6.6 times higher than the density of the heaviest metal on Earth - iridium), and the temperature in the center of the core is more than 14 million K.

Because The highest temperatures and densities should be in the central parts of the Sun; nuclear reactions and the accompanying energy release occur most intensely near the very center of the Sun. In the nucleus, along with the proton-proton reaction, the carbon cycle plays a significant role.

As a result of the proton-proton reaction alone, 4.26 million tons of matter are converted into energy every second, but this value is insignificant compared to the mass of the Sun - 2·1027 tons. Internal structure of the Sun.

Radiant Equilibrium Zone

As you move away from the center of the Sun, the temperature and density become lower, the release of energy due to the carbon cycle quickly stops, and up to a distance of 0.2–0.3 radius, the temperature becomes less than 5 million K, and the density also drops significantly. As a result, nuclear reactions practically do not occur here. These layers only transmit radiation that occurs at greater depths outward.

It is significant that instead of each absorbed quantum of high energy, particles, as a rule, emit several quanta of lower energies as a result of successive cascade transitions. Therefore, instead of γ-quanta, X-rays appear, instead of X-rays, UV quanta appear, which, in turn, are already in the outer layers “fragmented” into quanta of visible and thermal radiation, finally emitted by the Sun.

That part of the Sun in which the release of energy due to nuclear reactions is insignificant and the process of energy transfer occurs only through absorption of radiation and subsequent re-emission is called the radiative equilibrium zone. It occupies an area from approximately 0.3 to 0.7 solar radii.

Convective zone

Above the level of radiative equilibrium, the substance itself begins to take part in energy transfer.

Directly below the observable outer layers of the Sun, over about 0.3 of its radius, a convective zone is formed in which energy is transferred by convection.

In the convective zone, vortex mixing of the plasma occurs. According to modern data, the role of the convective zone in the physics of solar processes is exceptionally great, since it is in it that various movements of solar matter and magnetic fields originate.

The structure of the solar atmosphere. Photosphere

The outermost layers of the Sun (the solar atmosphere) are usually divided into the photosphere, chromosphere and corona.

The photosphere is that part of the solar atmosphere in which visible radiation is formed, which has a continuous spectrum. Thus, almost all solar energy coming to us is emitted in the photosphere. The photosphere is visible when directly observing the Sun in white light in the form of its apparent “surface”.

The thickness of the photosphere, i.e. The length of the layers, from where more than 90% of the radiation in the visible range comes, is less than 200 km, i.e. about 3·10–4 R. As calculations show, when observed tangentially to such layers, their apparent thickness decreases several times, as a result of which, near the very edge of the solar disk (limb), the fastest drop in brightness occurs over a period of less than 10–4 R. For this reason, the edge of the Sun appears exceptionally sharp. The concentration of particles in the photosphere is 1016–1017 per 1 cm3 (under normal conditions, 1 cm3 of the earth’s atmosphere contains 2.7 1019 molecules). The pressure in the photosphere is about 0.1 atm, and the temperature of the photosphere is 5,000 - 7,000 K.

Under such conditions, atoms with ionization potentials of several volts (Na, K, Ca) are ionized. The remaining elements, including hydrogen, remain predominantly in a neutral state.

The photosphere is the only region of neutral hydrogen on the Sun. However, as a result of insignificant ionization of hydrogen and almost complete ionization of metals, it still contains free electrons. These electrons play an extremely important role: when they combine with neutral hydrogen atoms, they form negative hydrogen ions H -

Negative hydrogen ions are formed in negligible quantities: out of 100 million hydrogen atoms, on average, only one turns into a negative ion.

H– ions have the property of unusually strongly absorbing radiation, especially in the IR and visible regions of the spectrum. Therefore, despite their insignificant concentration, negative hydrogen ions are the main reason determining the absorption of radiation in the visible region of the spectrum by photospheric matter. The bond of the second electron to the atom is very weak, and therefore even IR photons can destroy the negative hydrogen ion.

Radiation occurs when electrons are captured by neutral atoms. Formed upon capture

photons determine the glow of the photospheres of the Sun and stars close to it in temperature. Thus, yellowish

The light of the Sun, which is commonly called “white,” arises when another electron is added to a hydrogen atom.

The electron affinity of a neutral H atom is 0.75 eV. When an electron is added to the H atom ( e) with energy greater than 0.75 eV, its excess is carried away by electromagnetic radiation e+H → H– + ħ ω, a significant part of which falls in the visible range.

Observations of the photosphere reveal its fine structure, reminiscent of closely spaced cumulus clouds. Light round formations are called granules, and the entire structure is called granulation. The angular dimensions of the granules on average are no more than 1" arc, which corresponds to 725 km on the Sun. Each individual granule exists for an average of 5–10 minutes, after which it disintegrates, and in its place appear

The granules are surrounded by dark spaces, forming cells or honeycombs. The spectral lines in the granules and in the spaces between them are shifted to the blue and red sides, respectively. This means that the substance in the granules rises and around them sinks. The speed of these movements is 1–2 km/s.

Granulation is a manifestation of the convective zone located under the photosphere observed in the photosphere. In the convective zone, active mixing of matter occurs as a result of the rise and fall of individual masses of gas (convection elements). Having traveled a path approximately equal to their size, they seem to dissolve in the environment, giving rise to new heterogeneities. In the outer, colder layers,

the sizes of these inhomogeneities are smaller

Chromosphere

In the outer layers of the photosphere, where the density decreases to 3×10-8 g/cm3, the temperature reaches values ​​below 4,200 K. This temperature value turns out to be the minimum for the entire solar atmosphere. In higher layers, the temperature begins to increase again. First, there is a slow increase in temperature to several tens of thousands of kelvins, accompanied by the ionization of hydrogen and then helium. This part of the solar atmosphere is called the chromosphere.

The reason for such strong heating of the outermost layers of the solar atmosphere is the energy of acoustic (sound) waves, which arise in the photosphere as a result of the movement of convection elements.

In the uppermost layers of the convective zone, directly below the photosphere, convective movements are sharply slowed down and convection suddenly stops. Thus, the photosphere from below is constantly, as it were, “bombarded” by convective elements. From these impacts, disturbances arise in it, observed in the form of granules, and it itself begins to oscillate with a period corresponding to the frequency of the photosphere’s own oscillations (about 5 minutes). These vibrations and disturbances that arise in the photosphere generate waves in it that are close in nature to sound waves in the air. When spreading upward, i.e. into layers with lower density, these waves increase their amplitude to several kilometers and turn into

shock waves.

The length of the chromosphere is several thousand km. The chromosphere has an emission spectrum consisting of bright lines. This spectrum is very similar to the spectrum of the Sun, in which all absorption lines are replaced by emission lines, and there is almost no continuous spectrum. However, in the spectrum of the chromosphere, the lines of ionized elements are stronger than in the spectrum of the photosphere. In particular, helium lines are very strong in the spectrum of the chromosphere, while in the Fraunhofer spectrum they are practically invisible. These spectral features confirm an increase in temperature in the chromosphere.

When studying images of the chromosphere, the first thing that attracts attention is its inhomogeneous structure, which is much more pronounced than granulation in the photosphere.

The smallest structural formations in the chromosphere are called spicules. They have an oblong shape, and are elongated mainly in the radial direction. Their length is several thousand km, and their thickness is about 1,000 km. At speeds of several tens of km/s, spicules rise from the chromosphere into the corona and dissolve in it.

Through spicules, the substance of the chromosphere is exchanged with the overlying corona.

There are hundreds of thousands of spicules existing on the Sun at the same time.

The spicules in turn form a larger structure called the chromospheric network, generated by wave motions caused by much larger and deeper elements

subphotospheric convective zone than granules.

The chromospheric network is best seen in images with strong lines in the far UV region of the spectrum,

for example, in the 304 Å resonance line of ionized helium.

The chromospheric network consists of individual cells ranging in size from 30 to 60 thousand km.

Crown

In the upper layers of the chromosphere, where the gas density is only 10–15 g/cm3, another unusually sharp increase in temperature occurs, to about a million kelvins. This is where the outermost and thinnest part of the Sun's atmosphere, called the solar corona, begins.

The brightness of the solar corona is a million times less than the photosphere, and does not exceed the brightness of the Moon at full moon. Therefore, the solar corona can be observed during the total phase of solar eclipses, and outside of eclipses - with the help of special telescopes (coronagraphs), in which an artificial eclipse of the Sun is arranged.

The crown does not have sharp outlines and has an irregular shape that changes greatly over time. This can be judged by comparing its images obtained during various eclipses. The brightest part of the corona, located no more than 0.2-0.3 solar radii from the limb, is usually called the inner corona, and the rest, a very extended part, is the outer corona. An important feature of the crown is its radiant structure. The rays come in various lengths up to a dozen or more solar radii. At the base, the rays usually thicken, some of them bend towards the neighboring ones.

The spectrum of the corona has a number of important features. It is based on a weak continuous background with an energy distribution that repeats the energy distribution in the continuous spectrum of the Sun. Against this background

continuous spectrum, bright emission lines are observed in the inner corona, the intensity of which decreases with distance from the Sun. Most of these lines cannot be obtained in laboratory spectra. In the outer corona, Fraunhofer lines of the solar spectrum are observed, which differ from the photospheric lines in their relatively greater residual intensity.

The corona radiation is polarized, and at a distance of about 0.5 Rfrom the edge of the Sun the polarization increases to approximately 50%, and at greater distances it decreases again.__

Corona radiation is scattered light from the photosphere, and the polarization of this radiation makes it possible to establish the nature of the particles on which scattering occurs - these are free electrons.

The appearance of these free electrons can only be caused by the ionization of the substance. However, in general, the ionized gas (plasma) must be neutral. Therefore, the concentration of ions in the corona must also correspond to the concentration of electrons.

The emission lines of the solar corona belong to ordinary chemical elements, but in very high stages of ionization. The most intense - green coronal line with a wavelength of 5303 Å - is emitted by the Fe XIV ion, i.e. an iron atom lacking 13 electrons. Another intense one - the red coronal line (6,374 Å) - belongs to the atoms of ninefold ionized iron Fe X. The remaining emission lines are identified with the ions Fe XI, Fe XIII, Ni XIII, Ni XV, Ni XVI, Ca XII, Ca XV, Ar X and etc.

Thus, the solar corona is a rarefied plasma with a temperature of about a million kelvins.

Zodiacal light and counterradiance

A glow similar to the “false corona” can also be observed at great distances from the Sun in

form of zodiacal light.

Zodiacal light is observed on dark moonless nights in spring and autumn in southern latitudes soon

after sunset or shortly before sunrise. At this time, the ecliptic rises high above the horizon, and a light stripe running along it becomes noticeable. As it approaches the Sun, which is below the horizon, the glow intensifies and the stripe expands, forming a triangle. Its brightness gradually decreases with increasing distance from the Sun.

In the area of ​​the sky opposite the Sun, the brightness of the zodiacal light increases slightly, forming an elliptical nebulous spot with a diameter of about 10º, which is called the antiradiance. Counter-shine

caused by the reflection of sunlight from cosmic dust.

sunny wind

The solar corona has a dynamic continuation far beyond the Earth's orbit to distances of the order of 100 AU.

There is a constant outflow of plasma from the solar corona at a speed that gradually increases with distance from the Sun. This expansion of the solar corona into interplanetary space is called the solar wind.

Due to the solar wind, the Sun loses about 1 million tons of matter every second. The solar wind consists primarily of electrons, protons, and helium nuclei (alpha particles); the nuclei of other elements and neutral particles are contained in very small quantities.

The solar wind (the flow of particles - protons, electrons, etc.) is often confused with the pressure effect of sunlight (the flow of photons). The pressure of sunlight is currently several thousand times greater than the pressure of the solar wind. The tails of comets, always directed in the opposite direction from the Sun, are also formed due to the pressure of light, and not due to the solar wind.

38. Active formations in the solar atmosphere: spots, faculae, flocculi, chromospheric flares, prominences. Cyclicity of solar activity.

Active formations in the solar atmosphere

From time to time, rapidly changing active formations appear in the solar atmosphere, sharply different from the surrounding undisturbed regions, the properties and structure of which do not change at all or almost completely with time. In the photosphere, chromosphere and corona, the manifestations of solar activity are very different. However, they are all connected by a common reason. This reason is the magnetic field, always

present in active regions.

The origin and cause of changes in magnetic fields on the Sun are not fully understood. Magnetic fields can be concentrated in any layer of the Sun (for example, at the base of the convective zone), and periodic increases in magnetic fields can be caused by additional excitations of currents in the solar plasma.

The most common manifestations of solar activity are spots, faculae, flocculi, and prominences.

Sunspots

The most famous manifestation of solar activity are sunspots, which usually appear in entire groups.

The sunspot appears as a tiny pore, barely distinguishable from the dark spaces between the granules. After a day, the pore develops into a round dark spot with a sharp boundary, the diameter of which gradually increases up to a size of several tens of thousands of km. This phenomenon is accompanied by a gradual increase in the magnetic field strength, which in the center of large spots reaches several thousand oersteds. The magnitude of the magnetic field is determined by the Zeeman splitting of spectral lines.

Sometimes several small spots appear within a small area extended parallel to the equator - a group of spots. Individual spots predominantly appear on the western and eastern edges of the area, where the bottoms of the spot - the leading (western) and tail (eastern) - develop more strongly than others. The magnetic fields of both main sunspots and the small ones adjacent to them always have opposite polarity, and therefore such a group of sunspots is called bipolar

3-4 days after the appearance of large spots, a less dark penumbra appears around them, having a characteristic radial structure. The penumbra surrounds the central part of the sunspot, called the umbra.

Over time, the area occupied by a group of spots gradually increases, reaching its maximum

values ​​approximately on the tenth day. After this, the spots begin to gradually decrease and disappear, first the smallest of them, then the tail (having previously broken up into several spots), and finally the leading one.

In general, this entire process lasts about two months, but many groups of sunspots do not have time to

go through all the stages described and disappear earlier.

The central part of the spot only appears black due to the high brightness of the photosphere. In fact, in the center

The brightness of the spots is only an order of magnitude less, and the brightness of the penumbra is approximately 3/4 of the brightness of the photosphere. Based on the Stefan-Boltzmann law, this means that the temperature in the sunspot is 2–2.5 thousand K less than in the photosphere.

The decrease in temperature in the sunspot is explained by the influence of the magnetic field on convection. A strong magnetic field inhibits the movement of matter occurring across the lines of force. Therefore, in the convective zone under the sunspot, the circulation of gases, which transfers a significant part of the energy from the depths to the outside, is weakened. As a result, the temperature of the spot turns out to be lower than in the undisturbed photosphere.

The large concentration of the magnetic field in the shadow of the leading and tail sunspots suggests that the main part of the magnetic flux of the active region on the Sun is contained in a giant tube of field lines emerging from the shadow of the north polarity sunspot and entering back into the south polarity sunspot.

However, due to the high conductivity of solar plasma and the phenomenon of self-induction, magnetic fields with a strength of several thousand oersteds can neither arise nor disappear within a few days corresponding to the time of appearance and decay of a group of sunspots.

Thus, it can be assumed that magnetic tubes are located somewhere in the convective zone, and the appearance of groups of sunspots is associated with the floating of such tubes.

Torches

In undisturbed regions of the photosphere there is only a general magnetic field of the Sun, the strength of which is about 1 Oe. In active regions, the magnetic field strength increases hundreds and even thousands of times.

A slight increase in the magnetic field to tens and hundreds of Oe is accompanied by the appearance in the photosphere of a brighter region called a torch. In total, faculae can occupy a significant proportion of the entire visible surface of the Sun. They have a characteristic fine structure and consist of numerous veins, bright dots and nodules - torch granules.

The faculae are best visible at the edge of the solar disk (here their contrast with the photosphere is about 10%), while in the center they are almost completely invisible. This means that at some level in the photosphere the plume is hotter than the neighboring undisturbed region by 200–300 K and, on the whole, slightly protrudes above the level

undisturbed photosphere.

The appearance of a torch is associated with an important property of the magnetic field - it prevents the movement of ionized matter occurring across the lines of force. If the magnetic field has a sufficiently high energy, then it “allows” the movement of matter only along the lines of force.

A weak magnetic field in the plume region cannot stop relatively powerful convective movements. However, it can give them a more correct character. Typically, each element of convection, in addition to the general rise or fall in the vertical, makes small random movements in the horizontal plane. These movements, which lead to friction between the individual elements of convection, are inhibited by the magnetic field present in the plume region, which facilitates convection and allows hot gases to rise to a greater height and transfer a greater flow of energy. Thus, the appearance of the plume is associated with increased convection caused by a weak magnetic field.

Torches are relatively stable formations. They can exist for several weeks or even months without much change.

Floccules

The chromosphere above sunspots and faculae increases its brightness, and the contrast between the disturbed and undisturbed chromosphere increases with height. These brighter regions of the chromosphere are called flocculi. An increase in the brightness of a floccule compared to the surrounding undisturbed chromosphere does not provide grounds for determining its temperature, since in a rarefied and very transparent chromosphere for a continuous spectrum, the relationship between temperature and radiation does not obey the Planck and Stefan-Boltzmann laws.

The increase in the brightness of the floccule in the central parts can be explained by an increase in the density of matter in the chromosphere by 3–5 times at an almost constant temperature value, or with a slight increase in it. Solar flares

In the chromosphere and corona, most often in a small region between developing sunspots, especially near the polarity interface of strong magnetic fields, the most powerful and rapidly developing manifestations of solar activity, called solar flares, are observed.

At the beginning of the flare, the brightness of one of the light nodules of the flocculus suddenly increases. Often in less than a minute, strong radiation spreads along a long rope or floods an entire area tens of thousands of kilometers long.

In the visible region of the spectrum, the increase in luminescence occurs mainly in the spectral lines of hydrogen, ionized calcium and other metals. The level of the continuous spectrum also increases, sometimes so much that the flash becomes visible in white light against the background of the photosphere. Simultaneously with visible radiation, the intensity of UV and X-ray radiation, as well as the power of solar radio emission, increases greatly.

During flares, the shortest wavelength (i.e., the “hardest”) X-ray spectral lines and even, in some cases, γ-rays are observed. The burst of all these types of radiation occurs in a few minutes. After reaching the maximum, the radiation level gradually weakens over several tens of minutes.

All of these phenomena are explained by the release of a large amount of energy from unstable plasma located in the region of a very inhomogeneous magnetic field. As a result of the interaction of the magnetic field and plasma, a significant part of the energy of the magnetic field turns into heat, heating the gas to a temperature of tens of millions of kelvins, and also goes to accelerate plasma clouds.

Simultaneously with the acceleration of macroscopic plasma clouds, the relative movements of the plasma and magnetic fields lead to the acceleration of individual particles to high energies: electrons up to tens of keV and protons up to tens of MeV.

The flow of such solar particles has a significant impact on the upper layers of the Earth's atmosphere and its magnetic field.

Prominences

The active formations observed in the corona are prominences. Compared to the surrounding plasma, these are denser and “colder” clouds, glowing in approximately the same spectral lines as the chromosphere.

Prominences come in very different shapes and sizes. Most often these are long, very flat formations located almost perpendicular to the surface of the Sun. Therefore, when projected onto the solar disk, prominences look like curved filaments.

Prominences are the largest formations in the solar atmosphere, their length reaches hundreds of thousands of km, although their width does not exceed 6,000–10,000 km. Their lower parts merge with the chromosphere, and their upper parts extend for tens of thousands of km. However, there are prominences of much larger sizes.

The exchange of matter between the chromosphere and the corona constantly occurs through the prominences. This is evidenced by the frequently observed movements of both the prominences themselves and their individual parts, occurring at speeds of tens and hundreds of km/s.

The emergence, development and movement of prominences is closely related to the evolution of sunspot groups. At the first stages of development of the active region, short-lived and rapidly changing sunspots are formed.

prominences near sunspots. At later stages, stable quiet prominences appear, existing without noticeable changes for several weeks and even months, after which a stage of activation of the prominence may suddenly occur, manifested in the occurrence of strong movements, ejections of matter into the corona and the appearance of rapidly moving eruptive prominences.

Eruptive, or eruptive, resemble huge fountains in appearance, reaching heights of up to 1.7 million km above the surface of the Sun. The movements of clots of matter in them occur quickly; erupt at speeds of hundreds of km/s and change their shape quite quickly. As the altitude increases, the prominence weakens and dissipates. In some prominences, sharp changes in the speed of movement of individual clumps were observed. Eruptive prominences are short-lived.

Solar Activity

All considered active formations in the solar atmosphere are closely related to each other.

The appearance of flares and flocculi always precedes the appearance of spots.

Outbreaks occur during the most rapid growth of a group of sunspots or as a result of strong changes occurring in them.

At the same time, prominences appear, which often continue to exist for a long time after the collapse of the active region.

The totality of all manifestations of solar activity associated with a given part of the atmosphere and developing over a certain time is called the center of solar activity.

The number of sunspots and other associated manifestations of solar activity changes periodically. The era when the number of activity centers is greatest is called the maximum of solar activity, and when there are none or almost none at all, it is called the minimum.

As a measure of the degree of solar activity, the so-called. Wolf numbers proportional to the sum of the total number of spots f and ten times the number of their groups g: W= k(f+ 10g).

Proportionality factor k depends on the power of the tool used. Typically, Wolf numbers are averaged (for example, over months or years) and a graph of the dependence of solar activity on

The solar activity curve shows that maxima and minima alternate on average every 11 years, although the time intervals between individual successive maxima may

range from 7 to 17 years.

During the minimum period, there are usually no spots on the Sun for some time. They then begin to appear far from the equator, at approximately ±35° latitudes. Subsequently, the spot formation zone gradually descends towards the equator. However, in areas less than 8° from the equator, spots are very rare.

An important feature of the solar activity cycle is the law of changes in the magnetic polarity of sunspots. During each 11-year cycle, all leading spots of bipolar groups have some polarity in the northern hemisphere and the opposite in the southern hemisphere. The same is true for tail spots, in which the polarity is always opposite to that of the leading spot. In the next cycle, the polarity of the leading and tail spots is reversed. At the same time, the polarity of the general magnetic field of the Sun changes, the poles of which are located near the poles of rotation.

Many other characteristics also have an eleven-year cyclicity: the proportion of the Sun's area occupied by faculae and flocculi, the frequency of flares, the number of prominences, as well as the shape of the corona and

solar wind power.

The cyclicity of solar activity is one of the most important problems of modern solar physics, which has not yet been fully resolved.

When we observe a sunny summer landscape, it seems to us that the whole picture is flooded with light. However, if we look at the sun using special instruments, we will find that its entire surface resembles a giant sea, where fiery waves rage and spots move. What are the main components of the solar atmosphere? What processes occur inside our star and what substances are included in its composition?

Total information

The Sun is a celestial body that is a star, and the only one in the Solar System. Planets, asteroids, satellites and other space objects revolve around it. The chemical composition of the Sun is approximately the same at any point on it. However, it changes significantly as it approaches the center of the star, where its core is located. Scientists have discovered that the solar atmosphere is divided into several layers.

What chemical elements make up the Sun?

Humanity has not always had the data about the Sun that science has today. Once upon a time, supporters of the religious worldview argued that the world cannot be known. And as confirmation of their ideas, they cited the fact that it is not possible for a person to know what the chemical composition of the Sun is. However, progress in science has convincingly proven the fallacy of such views. Scientists have especially advanced in the study of stars after the invention of the spectroscope. Scientists study the chemical composition of the Sun and stars using spectral analysis. So, they found out that the composition of our star is very diverse. In 1942, researchers discovered that there was even gold in the Sun, although not much of it.

Other substances

The chemical composition of the Sun mainly includes elements such as hydrogen and helium. Their predominance characterizes the gaseous nature of our star. The content of other elements, for example, magnesium, oxygen, nitrogen, iron, calcium, is insignificant.

Using spectral analysis, researchers found out what substances are definitely not on the surface of this star. For example, chlorine, mercury and boron. However, scientists suggest that these substances, in addition to the basic chemical elements that make up the Sun, may be located in its core. Almost 42% of our star consists of hydrogen. Approximately 23% comes from all the metals that are part of the Sun.

Like most parameters of other celestial bodies, the characteristics of our star are calculated only theoretically using computer technology. The initial data are indicators such as the radius of the star, its mass and its temperature. Scientists have now determined that the chemical composition of the Sun is represented by 69 elements. Spectral analysis plays a major role in these studies. For example, thanks to him the composition of the atmosphere of our star was established. An interesting pattern was also discovered: the set of chemical elements in the composition of the Sun is surprisingly similar to the composition of stony meteorites. This fact is important evidence that these celestial bodies have a common origin.

Fire crown

It is a layer of highly rarefied plasma. Its temperature reaches 2 million Kelvin, and the density of the substance exceeds the density of the earth’s atmosphere by hundreds of millions of times. Here the atoms cannot be in a neutral state; they constantly collide and ionize. The corona is a powerful source of ultraviolet radiation. Our entire planetary system is exposed to the solar wind. Its initial speed is almost 1 thousand km/sec, but as it moves away from the star it gradually decreases. The speed of the solar wind at the surface of the earth is approximately 400 km/sec.

General ideas about the crown

The solar crown is sometimes called the atmosphere. However, it is only its external part. The easiest time to observe the corona is during a total eclipse. However, it will be very difficult to sketch it, because the eclipse lasts only a few minutes. When photography was invented, astronomers were able to get an objective picture of the solar corona.

After the first images were taken, researchers were able to detect areas that are associated with increased activity of the star. The Sun's corona has a radiant structure. It is not only the hottest part of its atmosphere, but is also the closest to our planet. In fact, we are constantly within its boundaries, because the solar wind penetrates into the most distant corners of the solar system. However, we are protected from its radiation effects by the earth's atmosphere.

Core, chromosphere and photosphere

The central part of our star is called the core. Its radius is equal to approximately a quarter of the total radius of the Sun. The matter inside the core is very compressed. Closer to the surface of the star is the so-called convective zone, where the movement of matter occurs, generating a magnetic field. Finally, the visible surface of the Sun is called the photosphere. It is a layer more than 300 km thick. It is from the photosphere that solar radiation comes to Earth. Its temperature reaches approximately 4800 Kelvin. Hydrogen here remains practically neutral. Above the photosphere is the chromosphere. Its thickness is about 3 thousand km. Although the chromosphere and the solar corona are located above the photosphere, scientists do not draw clear boundaries between these layers.

Prominences

The chromosphere has a very low density and is inferior in radiation intensity to the solar corona. However, an interesting phenomenon can be observed here: giant flames, the height of which is several thousand kilometers. They are called solar prominences. Sometimes prominences rise to a height of up to a million kilometers above the surface of the star.

Research

Prominences are characterized by the same density indicators as the chromosphere. However, they are located directly above it and are surrounded by its sparse layers. For the first time in the history of astronomy, prominences were observed by French researcher Pierre Jansen and his English colleague Joseph Lockyer in 1868. Their spectrum includes several bright lines. The chemical composition of the Sun and prominences is very similar. It mainly contains hydrogen, helium and calcium, and the presence of other elements is negligible.

Some prominences, having existed for a certain period of time without visible changes, suddenly explode. Their substance is ejected into nearby outer space at a gigantic speed, reaching several kilometers per second. The appearance of the chromosphere often changes, which indicates various processes occurring on the surface of the Sun, including the movement of gases.

In regions of the star with increased activity, one can observe not only prominences, but also spots, as well as increased magnetic fields. Sometimes, with the help of special equipment, flares of especially dense gases are detected on the Sun, the temperature of which can reach enormous values.

Chromospheric flares

Sometimes the radio emission from our star increases hundreds of thousands of times. This phenomenon is called a chromospheric flare. It is accompanied by the formation of spots on the surface of the Sun. At first, the flares were noticed in the form of an increase in the brightness of the chromosphere, but later it turned out that they represent a whole complex of different phenomena: a sharp increase in radio emission (X-ray and gamma radiation), mass ejection from the corona, proton flares.

Drawing conclusions

So, we found out that the chemical composition of the Sun is mainly represented by two substances: hydrogen and helium. Of course, there are other elements, but their percentage is low. In addition, scientists have not discovered any new chemical substances that would be part of the star and would not be present on Earth. Visible radiation is formed in the solar photosphere. It, in turn, is of enormous importance for maintaining life on our planet.

The sun is a hot body that continuously emits. Its surface is surrounded by a cloud of gases. Their temperature is not as high as that of the gases inside the star, but it is still impressive. Spectral analysis allows us to find out from a distance what the chemical composition of the Sun and stars is. And since the spectra of many stars are very similar to the spectra of the Sun, this means that their composition is approximately the same.

Today, the processes occurring on the surface and inside the main star of our planetary system, including the study of its chemical composition, are studied by astronomers in special solar observatories.

Like any planet or star, The sun has its own atmosphere. By it we mean such outer layers from where at least part of the radiation can freely escape into the surrounding space without being absorbed by the overlying layers. Our star consists entirely of gas. Its atmosphere begins 200-300 km deeper than the visible edge of the solar disk. These deepest layers are called photosphere. Since their thickness is no more than one thousandth of the solar radius (from 100 to 400 km), the photosphere is sometimes called surface of the Sun. The density of gases in the photosphere is hundreds of times less than at the Earth's surface. The temperature of the photosphere decreases from 8000 K at a depth of 300 km to 4000 K in the uppermost layers. The average effective temperature perceived by the Earth can be calculated from the Stefan-Boltzmann equation and is 5778 K. Under such conditions, almost all gas molecules disintegrate into individual atoms. Only in the uppermost layers are relatively few simple molecules of the type H 2, OH, CH.
If you examine the Sun through a telescope with high magnification, you can observe thin layers of the photosphere: all of it seems strewn with small bright grains - granules, separated by a network of narrow dark paths. Granulation results from the mixing of warmer gas flows and descending cooler ones. Convection in the outer layers of the Sun plays a huge role in determining the overall structure of the atmosphere. Ultimately, it is convection, as a result of complex interaction with solar magnetic fields, that is the cause of all the diverse manifestations of solar activity.
Photosphere forms the visible surface of the Sun, from which the size of the star, the distance from the surface of the Sun to other celestial bodies, etc. are determined.

The photosphere is the visible disk of the Sun. In Fig. a small dark area is visible,

which is called a sunspot. The temperature in such areas is much

lower compared to the surrounding atmosphere and reaches only 1500 K.

The photosphere gradually passes into the more rarefied outer solar layers of the atmosphere - chromosphere and corona. Chromosphere so named for its reddish-purple color. It can only be seen with the naked eye for a few seconds during a total solar eclipse (when the Moon completely covers (eclipses) the Sun from an observer on Earth, i.e. the centers of the Earth, Moon and Sun are on the same line). The chromosphere is very heterogeneous and consists mainly of elongated elongated tongues (spicules). The temperature of these chromospheric jets is two to three times higher than in the photosphere and increases with height from 4000 to 15,000 K., and the density is hundreds of thousands of times less. The total length of the chromosphere is 10-15 thousand kilometers. The increase in temperature will be explained by the propagation of waves and magnetic fields penetrating into it from the convective zone.

The chromosphere of the Sun observed during total

solar eclipse

Chromosphere It is customary to divide it into two zones:

— lower chromosphere- extends to approximately 1500 km, consists of neutral hydrogen, its spectrum contains a large number of weak spectral lines;

— upper chromosphere- formed from individual spicules ejected from the lower chromosphere to a height of up to 10,000 km and separated by more rarefied gas.

Often during eclipses (and with the help of special spectral instruments - and without waiting for eclipses) above the surface of the Sun one can observe bizarrely shaped “fountains”, “clouds”, “funnels”, “bushes”, “arches” and other brightly luminous formations from the chromospheric substances. From time to time, jets, clouds and arches of hot gas rise from the chromosphere, called prominences. During a total solar eclipse they are visible to the naked eye. Some prominences float calmly, others rise at speeds of several hundred kilometers per second to a height reaching the solar radius. Prominences have approximately the same density and temperature as the chromosphere. But they are above it and surrounded by higher, highly rarefied upper layers of the solar atmosphere. Prominences do not fall into the chromosphere because their matter is supported by the magnetic fields of active regions of the Sun. The spectrum of prominences, like the chromosphere, consists of bright lines, mainly hydrogen, helium and calcium. Emission lines from other chemical elements are also present, but they are much weaker. Some prominences, having remained for a long time without noticeable changes, suddenly seem to explode, and their matter is thrown into interplanetary space at a speed of hundreds of kilometers per second.

A prominence is a giant fountain of hot gas that

rises to heights of tens and hundreds of thousands of kilometers and

held above the surface of the Sun by a magnetic field.

Solar prominence in comparison with our planet

Sometimes explosion-like things happen in very small areas solar atmosphere. These are the so-called chromospheric flares. They usually last several tens of minutes. During flares in the spectral lines of hydrogen, helium, ionized calcium and some other elements, the glow of a separate section of the chromosphere suddenly increases tens of times. Ultraviolet and X-ray radiation increases especially strongly: sometimes its power is several times higher than the total radiation power of the Sun in this short-wave region of the spectrum before the flare. Flashes- the most powerful explosion-like processes observed on the Sun. They can last only a few minutes, but during this time energy is released, which can sometimes reach 10 25 J. Approximately the same amount of body comes from the Sun to the entire surface of the Earth in a whole year.
Spots, torches, prominences, chromospheric flares - all these are manifestations of solar activity. With increasing activity, the number of these formations on the Sun increases.

The outer layer of the Sun's atmosphere includes the solar Crown.It extends for many millions of kilometers, and its border continues to the very end of the entire solar system. Naturally, all the planets, including our Earth, are under a huge solar dome. The solar corona begins immediately after the chromosphere and consists of fairly rarefied gas. The temperature of the corona is about a million Kelvin. Moreover, it increases from the chromosphere up to two million at a distance of the order 70000 km from the visible surface of the Sun, and then begins to decrease, reaching one hundred thousand degrees near the Earth.

Due to the enormous temperature, the particles move so quickly that during collisions, electrons fly off from the atoms, which begin to move as free particles. As a result of this, light elements completely lose all their electrons, so that there are practically no hydrogen or helium atoms in the corona, but only protons and alpha particles. Heavy elements lose up to 10-15 outer electrons. For this reason, unusual spectral lines are observed in the solar corona, which for a long time could not be identified with known chemical elements.

The gaseous envelope surrounding our planet Earth, known as the atmosphere, consists of five main layers. These layers originate on the surface of the planet, from sea level (sometimes below) and rise to outer space in the following sequence:

• Troposphere;
• Stratosphere;
• Mesosphere;
• Thermosphere;
• Exosphere.

Diagram of the main layers of the Earth's atmosphere

In between each of these main five layers are transition zones called "pauses" where changes in air temperature, composition and density occur. Together with pauses, the Earth's atmosphere includes a total of 9 layers.

Troposphere: where weather occurs

Of all the layers of the atmosphere, the troposphere is the one with which we are most familiar (whether you realize it or not), since we live on its bottom - the surface of the planet. It envelops the surface of the Earth and extends upward for several kilometers. The word troposphere means "change of the globe." A very appropriate name, since this layer is where our everyday weather occurs.

Starting from the surface of the planet, the troposphere rises to a height of 6 to 20 km. The lower third of the layer, closest to us, contains 50% of all atmospheric gases. This is the only part of the entire atmosphere that breathes. Due to the fact that the air is heated from below by the earth's surface, which absorbs the thermal energy of the Sun, the temperature and pressure of the troposphere decrease with increasing altitude.

At the top there is a thin layer called the tropopause, which is just a buffer between the troposphere and the stratosphere.

Stratosphere: home of the ozone

The stratosphere is the next layer of the atmosphere. It extends from 6-20 km to 50 km above the Earth's surface. This is the layer in which most commercial airliners fly and hot air balloons travel.

Here the air does not flow up and down, but moves parallel to the surface in very fast air currents. As you rise, the temperature increases, thanks to the abundance of naturally occurring ozone (O3), a byproduct of solar radiation and oxygen, which has the ability to absorb the sun's harmful ultraviolet rays (any increase in temperature with altitude in meteorology is known as an "inversion") .

Because the stratosphere has warmer temperatures at the bottom and cooler temperatures at the top, convection (vertical movement of air masses) is rare in this part of the atmosphere. In fact, you can view a storm raging in the troposphere from the stratosphere because the layer acts as a convection cap that prevents storm clouds from penetrating.

After the stratosphere there is again a buffer layer, this time called the stratopause.

Mesosphere: middle atmosphere

The mesosphere is located approximately 50-80 km from the Earth's surface. The upper mesosphere is the coldest natural place on Earth, where temperatures can drop below -143°C.

Thermosphere: upper atmosphere

After the mesosphere and mesopause comes the thermosphere, located between 80 and 700 km above the surface of the planet, and contains less than 0.01% of the total air in the atmospheric envelope. Temperatures here reach up to +2000° C, but due to the extreme thinness of the air and the lack of gas molecules to transfer heat, these high temperatures are perceived as very cold.

Exosphere: the boundary between the atmosphere and space

At an altitude of about 700-10,000 km above the earth's surface is the exosphere - the outer edge of the atmosphere, bordering space. Here weather satellites orbit the Earth.

What about the ionosphere?

The ionosphere is not a separate layer, but in fact the term is used to refer to the atmosphere between 60 and 1000 km altitude. It includes the uppermost parts of the mesosphere, the entire thermosphere and part of the exosphere. The ionosphere gets its name because in this part of the atmosphere the radiation from the Sun is ionized when it passes through the Earth's magnetic fields at and. This phenomenon is observed from the ground as the northern lights.

The Sun, the central body of the Solar System, is a very hot plasma ball. The sun is the closest star to the earth. The light from it reaches us in 8 1/3 minutes. The Sun had a decisive influence on the formation of all bodies in the Solar System and created the conditions that led to the emergence and development of life on Earth.

The radius of the Sun is 109 times, and the volume is approximately 1,300,000 times greater than the radius and volume of the Earth, respectively. The mass of the Sun is also great. It is approximately 330,000 times the mass of the Earth and almost 750 times the total mass of the planets moving around it.

The Sun probably arose along with other bodies of the Solar System from a gas and dust nebula. About 5 billion years ago. At first, the substance of the Sun became very hot due to gravitational compression, but soon the temperature and pressure in the depths increased so much that nuclear reactions began to occur spontaneously. As a result of this, the temperature in the center of the Sun rose very much, and the pressure in its depths increased so much that it was able to balance the force of gravity and stop the gravitational compression. This is how the modern structure of the Sun arose. This structure is maintained by the slow conversion of hydrogen into helium occurring in its depths. Over the 5 billion years of the Sun's existence, about half of the hydrogen in its central region has already turned into helium. As a result of this process, the amount of energy that the Sun emits into space is released.

The radiation power of the Sun is very high: it is equal to 3.8×10 20 MW. A tiny fraction of solar energy reaches the Earth, amounting to about half a billionth. It maintains the earth's atmosphere in a gaseous state, constantly heats land and water bodies, gives energy to winds and waterfalls, and ensures the vital activity of animals and plants. Part of the solar energy is stored in the bowels of the Earth in the form of coal, oil and other minerals.

The sun is a spherically symmetrical body in equilibrium. Everywhere at the same distances from the center of this ball, the physical conditions are the same, but they change noticeably as you approach the center. Density and pressure quickly increase in depth, where the gas is more strongly compressed by the pressure of the layers above. Consequently, the temperature also increases as it approaches the center. Depending on changes in physical conditions, the Sun can be divided into several concentric layers, gradually transforming into each other.

At the center of the Sun, the temperature is 15 million degrees, and the pressure exceeds hundreds of billions of atmospheres. The gas is compressed here to a density of about 1.5x10 5 kg/m 3. Almost all of the Sun's energy is generated in a central region with a radius of approximately 1/3 that of the Sun. Through the layers surrounding the central part, this energy is transferred outward. Over the last third of the radius there is a convective zone. The reason for mixing (convection) in the outer layers of the Sun is the same as in a boiling kettle: the amount of energy coming from the heater is much greater than that removed by thermal conductivity. Therefore, the substance is forced to move and begins to transfer heat on its own.

The layers of the Sun are virtually unobservable. Their existence is known either from theoretical calculations or on the basis of indirect data. Above the convective zone are the directly observable layers of the Sun, called its atmosphere. They are better studied, since their properties can be judged from observations.

The internal structure of the Sun is layered, or shell-like, it is differentiated into spheres, or regions. In the center is core, then radial energy transfer region, Further convective zone and finally atmosphere. A number of researchers include three external areas: photosphere, chromosphere and corona. True, other astronomers consider only the chromosphere and corona to be the solar atmosphere.

Core- the central region of the Sun with ultra-high pressure and temperature, ensuring the flow of nuclear reactions. They release enormous amounts of electromagnetic energy in extremely short wavelength ranges.

Region of beam energy transfer is located above the core. It is formed by practically motionless and invisible ultra-high-temperature gas. The energy generated in the core is transferred through it to the outer spheres of the Sun by beam method, without moving gas. This process should be imagined something like this. From the core to the region of radiation transfer, energy enters in extremely short-wave ranges - gamma radiation, and leaves in longer-wave x-rays, which is associated with a decrease in gas temperature towards the peripheral zone.

Convective region is located above the previous one. It is also formed by invisible hot gas in a state of convective mixing. It is due to the position of the region between two environments that differ sharply in the pressure and temperature prevailing in them. The transfer of heat from the solar interior to the surface occurs as a result of local uplifts of highly heated air masses under high pressure to the periphery of the star, where the temperature of the gas is lower and where the light range of the Sun's radiation begins. The thickness of the convective region is estimated to be approximately 1/10 of the solar radius.