All stars apparently have a magnetic field. It was discovered on the Sun in 1908 by J. Hale (USA) from the Zeeman splitting of Fraunhofer lines in sunspots. According to modern concepts, it is ≈ 4000 Oe (intensity), or 0.4 T (magnetic induction). The field in spots is a manifestation of the general azimuthal field of the Sun, lines of force which have a different direction in the north and southern hemisphere.

Figure 56 The axisymmetric dipole component of the large-scale magnetic field of the Sun. Most

pronounced at the poles.

A weak dipole component of the magnetic field was discovered in 1953 by Babcock (USA) (≈1E or 10ˉ 4 T)

In the 70s of the 20th century, the same weak non-axisymmetric large-scale component of the magnetic field was discovered. It turned out to be associated with the interplanetary magnetic field, which has different directions in the radial components in different spatial sectors. This corresponds to a quadrupole whose axis lies in the plane of the solar equator. A two-sector structure corresponding to a magnetic dipole is also observed.

In general, the large-scale field of the Sun is complex. The structure of the field found on soft scales is even more complex. Observations indicate the existence of small-scale needle-like fields up to 2 * 10 3 Oe (induction 0.2 T). The sun's magnetic field is changing. The axisymmetric large-scale field changes with a period of ≈ 22 years. Every 11 years there is a reversal of the dipole component and a change in the direction of the azimuthal field.

The non-Semmitric component (sector) varies approximately with the period of the Sun's rotation around its axis. Small-scale fields change irregularly, chaotically.

The magnetic field is not essential for the equilibrium of the sun. The equilibrium state determines the balance of gravitational forces and pressure gradient. But all manifestations of solar activity (spots, flares, prominences, etc.) are associated with magnetic fields. The magnetic field plays a decisive role in the creation of the solar chromosphere and in heating up to a million degrees of the solar corona. The energy emitted in the ultraviolet and X-ray ranges is released in numerous localized regions identified with magnetic field loops. Regions in which radiation is weakened (coronal holes) are identified with configurations of magnetic field lines open to outer space. It is believed that streams originate in these areas solar wind.

1. Model of the internal structure of the Sun. Sources of solar energy.

Figure 57. Diagram of the structure of the sun.

The outer layers of the Sun (atmosphere) are directly observable. Therefore, theoretical models of their structure have been verified. Internal models are mostly theoretical. They are obtained by extrapolating physical conditions, on the surface and characteristics: size, mass, luminosity, rotation, chemical composition.

According to geological data, the age of the Sun is about 5 billion years. Its luminosity has changed little over the past 3 billion years. During these 3 billion years, the Sun has radiated 3.6 * 10 44 J, that is, each kilogram of the Sun's mass has released ~ 1.8 * 10 13 J of energy. Such an amount of energy, as calculations have shown, cannot provide chemical processes and gravity. (the gravitational energy of the Sun = 4 * 10 41 J).

The only possible, modern concept, the source of energy can be nuclear energy. If nuclear reactions are going on on the Sun and at the beginning all matter is hydrogen, then with the current luminosity of the Sun, nuclear energy would be enough for 170 billion years. For nuclear reactions to take place, a temperature of about ten million degrees is needed. Consequently, high luminosity implies a high temperature inside the Sun. According to observations in the photosphere, the temperature increases with depth with a gradient of 20 K per 1 km. This gives in the center ~ 1.4 * 10 6 K. The temperature can be estimated by the condition of hydrostatic equilibrium, considering the solar matter as an ideal gas: the gas pressure balances the forces of gravity. It turns out ≈ 14 * 10 6 K in the center, which is 3 times higher than the average.

The most significant in the interior of the Sun is proton - proton reaction... It begins with an extremely rare event - β - decay of one of the two protons at the moment of their especially close approach (14 * 10 9 years).

In β - decay, a proton turns into a neutron with the emission of a positron and neutrino. Combining with the second proton, the neutron gives the nucleus of heavy hydrogen - deuterium. For each pair of protons, the process takes an average of 14 billion years, which determines the slowness of thermonuclear reactions on the Sun and the total length of its evolution. Further nuclear transformations proceed much faster. Several options are possible, of which collisions of deuterium with a third proton and the formation of nuclei of the helium isotope should occur most often, which, combining and emitting two protons, give the nucleus of ordinary helium.

Another reaction under the conditions of the Sun plays a much smaller role. Ultimately, it also leads to the formation of a helium nucleus of four protons. The process is more complicated and can proceed only in the presence of carbon, the nuclei of which react at the first stages and are released at the latter. Thus, carbon is a catalyst, which is why the whole reaction is called carbon cycle.

During thermonuclear reactions in the interior of the Sun, it is released in the form of hard gamma quanta. When moving to the surface, they are repeatedly re-emitted, split into quanta of lower energy. The process takes millions of years. From one γ - quantum, several million quanta of visible light are formed, which leave the surface of the Sun.

In thermonuclear reactions, neutrinos are released. Due to its negligible mass and the absence of an electric charge, the neutrino interacts very weakly with matter. The Sun passes almost freely and flies out into interplanetary space at the speed of light. Its registration is difficult, but neutrinos can reap important information about the internal structure and conditions inside the Sun and stars.

Figure 58. Schematic section of the Sun and its

Like any ordinary star, the Sun is a giant self-gravitating ball of hot plasma - that is, a gas with a predominant content of charged particles (electrons, ions, etc.). These particles move at very high speeds in hot plasma. Where there are moving charged particles (electric current), there is also a magnetic field. The faster the charge moves, the stronger the magnetic field. Magnetic fields thus - the constant companions of the life of stars, including the sun. They also control many manifestations of the activity of stars: flares, ejections of matter, the formation of spots.

The sun has a large-scale magnetic field that slowly swirls around it due to its rotation. The "strength" of this field on the surface of the Sun is on average about 1 gauss (the unit of measurement of magnetic induction is a vector quantity that denotes the strength characteristic of the magnetic field at a given point in space). This can be compared to the magnetic field on the surface of the Earth. Sometimes, in certain areas of the Sun's surface, magnetic fields can increase - this leads to flares and causes coronal mass ejections - substances from the solar crust (outer layers of the Sun's atmosphere). When these fast streams of plasma reach the Earth's magnetosphere, they cause auroras, magnetic storms and other phenomena that affect people's lives. That is why the study of the magnetic fields of the Sun is considered not only a purely scientific, but also an applied task.

Mikhail Nagy / Rain

Dark spots on the surface of the Sun are also a manifestation of the local enhancement of the star's magnetic field. These spots are regions of the Sun's photosphere (the layer of the stellar atmosphere that gives the bulk of the radiation) with low temperatures. Observing sunspots and studying their magnetic fields is one of the daily tasks of modern heliophysics (a branch of astrophysics that studies the problems of solar physics). This is done by the Japanese space observatory Hinode, launched into orbit in 2006. With its help, in 2014, employees of the Japanese National Astronomical Observatory observed one of the pairs of spots that were then visible on the Sun (NOAA 11967).

The scientists observed a pair of spots, which allowed them to measure the magnitude of the magnetic field in different parts. They found that in the center of the larger spot, the field turned out to be about four thousand times greater than the average for the Sun. However, if this was expected, then the induction (force characteristic of the magnetic field) turned out to be even higher and amounted to a record 6250 Gauss.

What is the paradox of the discovery, as the scientists explained it and what is the special importance of the research - read in the material "The strongest magnetic field on the Sun was found where they did not expect" the popular science project "Elements".

In recent years, the theory of the structure of the sun and the phenomena on it have advanced greatly. In particular, on the basis of laboratory experiments with plasma, they came to the conclusion that magnetic fields on the Sun play a very important role in the phenomena observed on it.

Nuclear reactions take place in the core of the Sun, where the temperature is quite high - 16 million degrees. The radius of this zone, where energy is generated by nuclear reactions, is apparently about 200,000 km. With distance from the center of the Sun, the temperature drops rapidly - by 20 ° per kilometer. In this area, radiant energy is transferred by radiation. Before reaching one tenth of the radius to the photosphere, the temperature drops more slowly, and convection takes part in the transfer of energy in the form of a vertical rise of hot gases and a fall of cold gases. There is a mixing of the substance, which, however, is uneven in different directions.

In the photosphere, hydrogen atoms are mostly neutral, in the chromosphere, which is a transition layer, they ionize and complete ionization occurs in the corona. The thickness of the photosphere is only 200-300 km, that is, about V300 of the solar radius. Thus, the Sun's atmosphere consists of plasma - a mixture of ions and free electrons. The chromosphere, hundreds of thousands of times less dense than the photosphere, passes into the corona. Due to irradiation with the energy emitted by the photosphere, at its temperature of 6000 °, the thermometer in the chromosphere would show 5000 °, and even less in the corona. Particles of the rarefied gas of the chromosphere and corona would strike the thermometer so rarely that they could not heat it. However, the speeds of movement of particles in the chromosphere and corona are very high. It is known that the temperature of a gas can be measured by the kinetic energy of its particles. This is the so-called kinetic temperature. In the photosphere, the radiation temperatures and kinetic temperatures correspond to each other, but in the chromosphere and corona they differ sharply - in the chromosphere the kinetic temperature is tens of thousands of degrees, and in the corona - about a million degrees.

The "heating" of the chromosphere occurs due to the energy of waves propagating in it, generated by the motion of granules in the photosphere. In a corona extending to a distance of 10 solar radii, the number of atoms in 1 cm 3 is 100 billion times less than the number of molecules in 1 cm 3 of air at the surface of the Earth. At the same density as air, there would be enough matter in the corona for a layer surrounding the Sun, with a thickness of only a few millimeters. The main "radio emission of the Sun arises in it." With the same intensity as the corona, a heated body of the same size would emit at a temperature of a million degrees, and such a kinetic temperature is required, as we have seen, and the bright lines of multiply ionized metals observed in the spectrum of the corona.

The study of the interaction of the magnetic field and plasma has shown that the plasma as a whole is not affected by the motion along the lines of force of the magnetic field. When electrically charged particles move across the field lines (i.e., when current flows), an additional magnetic field arises. The addition of these magnetic fields causes the curvature and elongation of the lines of force following the movement of matter. Meanwhile, magnetic lines of force have a tension that tends to straighten them. This creates a magnetic pressure, and the field, preventing the plasma from crossing the lines of force, slows it down and can even drag it along if the field is strong. If it is weak, then the plasma moves the lines of force along with it. So, in all cases we can say that the lines of force are, as it were, “frozen” into the plasma.

This information, as well as regular measurements of the magnetic field strength in different places on the Sun, made it possible to approach the explanation of many phenomena on it.

The total magnetic field of the Sun is very weak, but it seems to play a big role. The corona beams, especially in the polar regions of the Sun, are located like lines of force that go out and enter at the poles of a magnetized ball. Changing the direction of the field in each hemisphere of the Sun from one solar cycle to the next is also very important. The reason for this change is not yet clear, but stars with very powerful magnetic fields are known, in which the polarity of the field also periodically changes.

When the Sun rotates, the fastest (equatorial) layers carry along the lines of force of the weak general field of the Sun, which are "frozen in" in them. These lines stretch out under the photosphere and wind around the Sun six times in three years, forming a tight spiral. If the lines of force are located closer together, it means that the overall (and distorted here) magnetic field of the Sun has increased.

Closer to the poles, the lines of force of the general field extend upward from the photosphere, and therefore the field does not increase here. However, at the equator itself, where the angular velocity of rotation in a certain zone changes little, the field also does not increase, and at latitudes + 30 °, where the rotation velocity changes most rapidly, the field enhancement is maximum. So, under the photosphere, similarities of tubes of condensed lines of force are formed. The gas pressure in them is added to the pressure of the magnetic field perpendicular to its lines. The gas in the "tube" expands and becomes, as it were, lighter and can "float" upward. In this place, where it approaches the surface, an increase in the magnetic field is observed on the Sun, and then the appearance of a torch, and behind it the field of torches. Their hot gases rise higher than neighboring places in the photosphere, because the weak magnetic field around them dampens small turbulent movements that tend to slow down the flow of hot escaping gas. Heating also occurs above the torches in the chromosphere and hot floccules appear. Finally, a brighter glow begins above the flocculi in the crown. This is how the active region on the Sun develops. Ascending to the surface and crossing it, the tube with condensed lines of force forms local amplifications of the magnetic field and sunspots appear. Their lower temperature is due to the fact that a very strong magnetic field in this region suppresses not only turbulence, but also strong convective motions. Therefore, here the inflow of hot gases from below stops, while around the spot, in the area of ​​torches and floccules, convection by a weak magnetic field is enhanced, since it suppresses weak turbulence and there the inflow of hot gases from below is facilitated. It is clear that the intersection of the curved tube with this surface in two places causes opposite magnetic polarities at the two main spots. The exit of the tube from the photosphere and the scattering of its lines lead to fragmentation and disappearance of the two main spots formed by the intersection of the flux tube with the surface of the Sun. The exit of the lines of force of the tube into the rarefied chromosphere and corona, where the gas pressure is less than the pressure of the magnetic field, leads to the fact that the lines diverge, forming loops and arcs.

Gradually, the areas of activity with the magnetic tubes that generate them in the eastern part form spots with polarities opposite to that which was at the beginning of the cycle at this pole of the Sun. This causes first the neutralization of the former general magnetic field, and then, three years before the end of the 11-year cycle of solar activity, creates a general field of opposite polarity.

After 11 years, the former picture of the polarities of the general field is restored.

Thus, in its main features, apparently, the correct explanation (given by Babcock), 22-year periodicity of solar activity, is obtained.

Chromospheric flares on the Sun are formed near the neutral points of magnetic fields in active regions, where the field strength rapidly increases with distance from these points. Here, an extremely rapid compression of the magnetic field takes place together with the plasma, into which it is "frozen", and the energy of the magnetic field is transformed into the radiation of the gas. Plasma is compressed into a thin cord and its temperature rises sharply - up to several tens of thousands of degrees. The density of the chromosphere increases here in a few minutes hundreds of thousands of times.

In addition to a huge increase in temperature, and with it radiation, especially ultraviolet and X-ray, the chromospheric flare also consists in the so-called burst of radio emission. At meter waves, the latter is amplified up to tens of millions of times.

The source of this radio emission moves from the chromosphere to the corona at a speed of about 1000 km / sec. Probably, it arises as a result of the emission of cosmic rays generated by the flare, and the bombardment of the plasma with these rays, which causes oscillations of the plasma, generating a burst of radio emission.

The rays observed in the corona are apparently generated by these streams of fast, electrically charged particles, pulling the lines of force of the magnetic field. Both this field and the corona plasma slow down particle flows, but some of them escape from the Sun's atmosphere and, falling into the Earth's atmosphere, produces auroras. The change in the picture of the solar magnetic field from the minimum of its activity to the maximum determines the changes in the shape of the corona, as we have already spoken about.

Many prominences, like corona rays, are caused by the movement of gas along the lines of force, which is why, for example, they are ejected along an arcuate trajectory and "roll down" them back to the surface of the Sun. Apparently, the prominences are located mainly in the areas of smooth changes in the magnetic field. The emergence of the glow of prominences suddenly at the top, and then their movement only downward is due, apparently, to processes similar to those which give chromospheric flares, but less sharp. Compression of the magnetic field leads to compression of the relatively cold gas, to an increase in its density and to luminescence.

These are the main features of the modern, mainly gas-magnetic, theory of solar phenomena.

Sunspots provide us with the most illustrative examples of non-stationary processes on the Sun. First of all, this is their rapid development. Sometimes two or three days are enough for a large sunspot or a large group of sunspots to develop in a "clean" place in the photosphere. As a rule, however, their development is slower and in large groups reaches a maximum in 2-3 weeks. Small spots and groups appear and disappear within a week, while large ones exist for several months. One spot is known that existed for 1.5 years. When a spot appears, when its penumbra is still small, the same photospheric granulation (Hansky, Thyssen) is visible in it, which, with further development, takes on a fibrous appearance; fibers are much more stable than pellets. When a round spot of regular shape approaches the solar edge, we observe it in projection and its diameter in the direction of the solar disk radius is greatly reduced (proportionally; see Fig. 8). In this case, the so-called Wilson effect is often observed, which consists in the fact that the penumbra of the spot is clearly visible from the side of the disk edge, and is strongly reduced from the side facing the center of the disk. This phenomenon allows the geometrical assimilation of a sunspot to a giant depression with conically tapering walls. But not all spots reveal this.

Usually a group of sunspots is stretched along heliographic longitude (in exceptional cases - up to 20 ° and more). At the same time, two of the largest sunspots with separate penumbraes are often outlined in a group, which have slightly different motions on the surface of the Sun. The eastern spot is called the leading one, the western one is called the next one. Such a tendency to form in pairs is often observed in individual sunspots that do not form groups with a large number of small satellite sunspots.

Rice. 38. Vortex structure of spots in the bipolar group. The directions of the vortices are opposite. (Spectrogram in the rays of Na)

Observations of radial velocities along different spectral lines in different parts of the sunspot and from different angles of view to it show the presence of strong (up to 3 km / s) movements in the penumbra of the sunspot - spreading of matter in its deep parts and flowing in of matter at a high altitude. The latter is confirmed by the vortex structure, which is noticeable above the spots on the spectroheliograms in the rays. The directions of these vortices are opposite in the southern and northern hemispheres of the Sun and indicate in single spots the inflow of matter in accordance with how it should be deflected by the Coriolis force.

Usually, on the outer edge of the penumbra, systematic movements are no longer observed.

As mentioned above, sunspots have strong magnetic fields. An intensity of 1000-2000 Oe is usual, and in one group at the end of February 1942, an intensity of 5100 Oe was measured. Detailed studies of the distribution of the direction and strength of the magnetic field inside the sunspot showed that in the center of the sunspot the magnetic field lines run along the axis of the sunspot (up or down), and as they move to the periphery of the sunspot, they deviate more and more from the normal to the surface, up to almost 90 ° at the edge of the penumbra. In this case, the magnetic field strength decreases from the maximum to almost zero.

Rice. 39. Change in the middle latitude and magnetic polarity of sunspots in successive cycles of solar activity

The larger the spot, the, as a rule, the stronger its magnetic field, but when a large spot, having reached its maximum size, begins to decrease, the strength of its magnetic field remains unchanged, and the total magnetic flux decreases in proportion to the area of ​​the spot. This can be interpreted as if the spot only contributes to the removal of the magnetic field outside, which exists for a long time under the surface. This is also confirmed by the fact that often the magnetic field does not disappear after the disappearance of the spot, but continues to exist there and is reinforced again with the new appearance of the spot in the same region. The presence of permanent flare fields here allows us to say that there are stable active areas in these places.

In groups with two large spots, the leading and next spots have opposite magnetic polarity (Figs. 38 and 39), which justifies the name of such groups - bipolar, as opposed to unipolar groups that include single spots. There are complex groups in which the spots of either polarity are randomly mixed. In each cycle of solar activity, the polarities of the leading and next spots in the northern and southern hemispheres are opposite to each other.

So, if in the northern hemisphere of the Sun the polarity of the leading sunspot is north (N), and the next one is south (S), then at the same time in the southern hemisphere the polarity of the leading sunspot is S, and the next one is N. In those rare sunspots that are crossed by the equator , the polarity of the north and south halves is opposite. But with the end of the cycle of solar activity, when its minimum passes, in each hemisphere, the distribution of magnetic polarity at the sunspots of the bipolar group changes to that which was in the previous cycle on the opposite hemisphere. This important fact was established by Hale and coworkers in 1913.

Although the local magnetic fields of the Sun are very strong, its general magnetic field is very weak and only with difficulty stands out against the background of local fields only during the years of sunspot minimums. Moreover, it is volatile. In the years 1953-1957, its intensity corresponded to a dipole with an induction of 1 G, the sign was opposite to the sign of the Earth's magnetic field, and the axis of the dipole coincided with the axis of rotation. In 1957, the sign of the field changed to the opposite in the southern polar regions of the Sun, and at the end of 1958 - in the northern regions. Last modified the field sign was observed in 1970-1971.

A change in the magnetic polarity of spots with the end of the solar cycle is not the only sign of the end of the cycle. Sunspots rarely form far from the equator. Their preferred zone lies within heliographic latitudes from 1-2 ° to 30 ° in both hemispheres. At the equator itself, spots are rare, as well as at latitudes above 30 °. But this picture has a peculiarity of its change in time: the first spots of the new cycle (after the imaginary) appear far from the equator (for example, spot с was recorded on March 15, 1914, from May 1943 and from October 1954), in while the last spots of the outgoing cycle are still observed near the equator. During the heyday of the cycle, near its maximum, sunspots can be found at all heliographic latitudes between - 45 ° and + 45 ° (a group of sunspots is known even with a latitude of + 50 °, observed in June 1957 during the maximum solar activity), but mainly between 5 and 20 °. Thus, the average heliographic latitude of sunspots steadily decreases with the development of the 11-year cycle of solar activity, and new sunspots appear closer and closer to the equator (Fig. 39). This pattern was first established in 1858 by Carrington and is sometimes called Spörer's law (although the latter established it 10 years later).

Thus, if by a period we mean a period of time during which all properties change and return to their original state, then the true period of solar activity is not 11 years, but 22 years. Interestingly, some alternation of the maximum height through the cycle also confirms the 22-year periodicity. An 80-year cycle of solar activity is also planned. For some internal reasons, solar activity varies widely with a characteristic time of about a century.

So, between 1645 and 1715. there were almost no sunspots on the sun, and the group appeared only once. This is the so-called Maunder minimum. Another minimum, the Spöhrer minimum, was between 1410 and 1510. On the contrary, the medieval high is between 1120 and 1280. was very energetic, like the one we are experiencing now. The described variations were accompanied by fluctuations in the average annual temperature in England within 1 ° C.

>> The magnetic field of the Sun

Do you have Sun's magnetic field: description and characteristics with photo, presence and role in Solar system, the appearance of sunspots and prominences, research.

The convective zone of the Sun is located under the upper layer of the photosphere (solar surface). It is inside it, as modern scientists say, that a magnetic field stars. Impossible to imagine a few great importance has a magnetic field in the processes taking place on the Sun. Most likely, it is a response to all active phenomena that occur in the atmosphere, including solar flares. That is, without it, the Sun would not be so interesting for the study of mankind.

Almost all objects recorded on the Sun originate under the influence of a magnetic field. First of all, these are, denoting the places of giant magnetic loops emerging from the depths of the Sun, crossing the solar surface. Because of this, the spots usually consist of north and south magnetic polarity. These areas are equal to the bases of the magnetic tube that emerges from the interior of the Sun. The cycles of solar activity are also influenced by the cyclical fluctuations of the magnetic field, which occurs in the interior of the Sun. Soaring above the surface of the Sun, visually as if hanging in the void, in fact, are penetrated by the threads of the magnetic field, based on it. And also, which we often observe in, is a simple repetition of the shape of the topology of the magnetic fields that surround them. Understanding all this allows us to calculate what magnetic situation on the Sun awaits us today and on any other day.

Methods for measuring the magnetic field of the Sun

Charged particles falling into a magnetic field move under its influence. In this case, electrons moving right-sided around the nucleus, under the influence of a magnetic field, increase energy, left-sided moving - it accordingly decreases. This so-called Zeemen effect splits the radiation of an atom into its components. By measuring the magnitude of the splitting, we are able to find out the magnitude and direction of the magnetic fields of distant objects that cannot be investigated directly, for example, the Sun. Determine with high accuracy the magnitude of the solar surface field allows the recent years but they are often ineffective when intending to measure the three-dimensional field in the sun's corona. In this case, using the methods of mathematics helps.

Knowledge of the nature and life of the Sun's magnetic field helps to make true predictions of the weather in space. The expectation of a new active solar flare can be determined at the present time by many indirect signs. However, at this stage of scientific processes, relatively long-term predictions of the time and duration of the ongoing solar cycles remain inaccurate. They are based more on the derivation of empirical dependencies, and not on specific physical models. The near future, we hope, will be able to explain quite well the behavior and activity of the Sun, and will make it possible, having correctly modeled its activity, to predict the weather in space no worse than the weather on Earth. Although it is already possible to accurately report the presence of a magnetic storm on the Sun today or on any calendar day.