Sun (astr. ☉) – single star solar system. Sun revolves around other objects of the system: the planets and their moons, dwarf planets and their moons, asteroids, meteors, comets and cosmic dust. Sun’s mass is 99.866% of the total mass of the solar system. Solar radiation sustains life on Earth (light is required for the initial stages of photosynthesis), determines the climate. Sun consists of hydrogen (~ 73% of the mass and ~ 92% by volume), helium (~ 25% of the mass and ~ 7% of ) and other elements with a lower concentration of iron, nickel, oxygen, nitrogen, silicon, sulfur, magnesium, carbon, neon, calcium and chromium . 1 million atoms of hydrogen for 98 000 atoms of helium, oxygen 851, 398 carbon atoms, 123 atoms of neon, 100 of nitrogen, 47 iron atoms, 38 atoms of magnesium, 35 silicon atoms and 16 sulfur atoms, 4 atoms of argon, 3 atoms of aluminum , 2 atom of nickel, sodium and calcium, as well as quite a bit of all the other elements. The average density of the Sun is 1.4 g / cm ³. The spectral classification of the type Sun G2V («yellow dwarf”). The surface temperature of the sun reaches 6000 K. Therefore, the sun shines almost white light, but the direct light of the sun on the surface of the planet gets some yellow tint because of the strong scattering and absorption of short-wave part of the spectrum of atmosphere (in a clear sky, with blue ambient light from sky, sunlight again gives white light).
The solar spectrum contains lines of ionized and neutral metals as well as ionized hydrogen. In our galaxy, the Milky Way, there are over 100 billion stars. With 85% of the stars in our galaxy – are stars fainter than the Sun (mostly red dwarfs). Like all main sequence stars, the sun produces energy through nuclear fusion. In the case of the vast majority of the solar energy produced in the synthesis of helium from hydrogen.
Distance of the Sun from the Earth, 149,600,000 miles, approximately astronomical unit, and the apparent angular diameter as seen from Earth as the moon – a little more than half a degree (31-32 minutes). The sun is located about 26,000 light years from the center of the Milky Way revolves around him, making one revolution more than 200 million years . Orbital velocity of the sun is 217 km / s – so it is a light-year of 1400 Earth years, and one astronomical unit – for 8 Earth days. Currently, the Sun is in the inner edge of the Orion arm of our galaxy, between the sleeve of Perseus and the Sagittarius arm, the so-called “local interstellar cloud” – an area of increased density, located, in turn, has a lower density in the “local bubble” – the area of scattered hot interstellar gas. Of the stars belonging to the closest 50 star systems within 17 light-years, currently known, the Sun is the fourth brightest star (its absolute magnitude 4,83 m).
Sun belongs to the first type of the stellar population. One of the common theories of the solar system suggests that its formation was caused by the explosion of one or more supernovae . This is based, in particular, on the fact that the matter of the solar system is contained abnormally high proportion of gold and uranium, which could be the result of endothermic reactions caused by the explosion, or nuclear transmutation of elements by neutron .
Radiation of the Sun – the main source of energy on Earth. Its capacity is characterized by the solar constant – the amount of energy passing through the area of unit area perpendicular to the sun. At a distance of one astronomical unit (that is, in the orbit of the Earth), this constant is about 1370 W / m ².
Passing through the Earth’s atmosphere, solar radiation loses energy is about 370 W / m ², and the earth’s surface reaches only 1,000 W / m ² (in clear weather, and when the sun is at the zenith). This energy can be used in a variety of natural and artificial processes. Thus, plants, using it through photosynthesis, synthesize organic compounds with oxygen. Direct sunlight or heat energy conversion using solar cells can be used to produce electricity (solar power) or do other useful work. By photosynthesis in the distant past was obtained and the energy stored in petroleum and other fossil fuels.
Ultraviolet radiation from the Sun has antiseptic properties make it suitable for disinfection of water and various objects. It also causes sunburn, and has other biological effects – for example, stimulates the production of vitamin D. Exposure to ultraviolet portion of the solar spectrum is strongly attenuated by the ozone layer in the earth’s atmosphere, so that the intensity of UV radiation at the Earth’s surface varies with latitude. The angle at which the sun is above the horizon at noon affects many types of biological adaptation – for example, it determines human skin color in different regions of the world.
Observed from the ground path of the sun over the sky changes throughout the year. The path described by a year the point at which the sun is in the sky at a particular given time is called the analemma and has a figure-8 shape, elongated along a north – south. The most notable variation in the apparent position of the sun in the sky – it swings along the north – south with amplitudes 47 ° (caused by tilting the plane of the ecliptic to the plane of the celestial equator, equal to 23,5 °). There is also another component of this variation, directed along the axis of the east – west and the resulting increase in the rate of orbital motion of the Earth in its approach to perihelion and reduction – when approaching aphelion. The first of these movements (north – south) is the cause of the seasons.
Earth passes through aphelion in early July and away from the Sun at a distance of 152 million km, and after perihelion – in early January and is close to the Sun at a distance of 147 million km . The apparent diameter of the Sun between the two dates is changed to 3% . Since the difference in distance is about 5 million km, the Earth at aphelion gets about 7% less heat. Thus, the winter in the northern hemisphere, a bit warmer than in the south, and the summer is a little cooler.
Sun – magnitnoaktivnaya star.
It has a strong magnetic field, the intensity of which varies with time and which changes direction approximately every 11 years, during the solar maximum. Variation of the magnetic field of the sun cause a variety of effects which together is called solar activity, and includes such phenomena as sunspots, solar flares, solar wind variations, etc., and on the Earth causes the aurora in the high and mid-latitudes and geomagnetic storms that have a negative impact on the work of communication, means of transmission, as well as a negative impact on living organisms (cause headaches and poor health in people who are sensitive to magnetic storms). It is assumed that the solar activity has played a major role in the formation and evolution of the solar system. It also affects the structure of the Earth’s atmosphere.
It is believed that the Sun was formed about 4.59 billion years ago when the fast compression by gravity clouds of molecular hydrogen led to the formation in our region of the galaxy star of the first type of the stellar population of T Tauri.
The star of this mass as the Sun, there should be on the main sequence for a total of about 10 billion years. So, now the sun is roughly in the middle of its life cycle. At the present stage in the solar core are thermonuclear reactions converting hydrogen into helium. Every second, the Sun’s core about 4 million tons of matter is converted into radiant energy, resulting in generated solar radiation and solar neutrino flux.
Mass of the sun is not enough to ensure that its evolution was completed by a supernova explosion. Instead, according to existing ideas, in 4-5 billion years, it will turn into a red giant. As soon as the hydrogen fuel in the core will burn, its outer shell will expand, and the kernel – compressed and heated. After about 7.8 billion years, when the temperature in the core reaches about 100 million K, it will begin thermonuclear fusion reaction of carbon and oxygen in helium. In this phase of the development of thermal instability in the Sun will lead to the fact that it will start to lose weight and drop the shell. Apparently, the expanding outer layers of the Sun at the time made the modern Earth’s orbit. In this study show that, even before this moment the sun weight loss will cause the earth to move farther from the Sun’s orbit and thus avoid the absorption of the outer layers of the solar plasma .
Despite this, all the water on Earth will go into a gaseous state, and its atmosphere is disrupted strong solar wind. Increasing the temperature of the sun at this time is that in the next 500-700 million years the Earth’s surface is too hot for her life could have existed in its modern sense. According to Professor J. Casting, loss of life due to the increase in temperature due to the increased brightness of the Sun , and possibly up to the red giant phase – in 1 billion years .
After the Sun will the red giant phase, thermal fluctuations lead to the fact that its outer shell will be disrupted, and it is formed of a planetary nebula. In the center of the nebula formed from the remains of very hot white dwarf core of the sun, which for many billions of years it will gradually cool and fade. This life cycle is typical for stars of low and average weight.
The central part of the Sun with a radius of about 150-175 thousand km (ie, 20-25% of the radius of the Sun), which are thermonuclear reactions, called a solar nucleus . The density of matter in the core is about 150 000 kg / m ³  (150 times higher than the density of water and ~ 6.6 times higher than the density of the dense metal on Earth – Os), and the temperature in the center of the core – more than 14 million K. Analysis of the data by the mission SOHO, showed that the core speed of the Sun around its axis is much higher than on the surface . The nucleus is the proton-proton fusion reaction, which resulted in four protons produced helium-4. In this case, every second light turn 4.26 million tons of matter, but this figure is insignificant compared to the mass of the Sun – 2.1027 tons. Power generated by different areas of the nucleus, depending on their distance to the center of the Sun. In the center it reaches, according to theoretical estimates, 276.5 W / m ³ . Thus, the volume of people (0.05m ³) have to heat 285 kcal / day (1192 kJ / day), which is much smaller than the specific heat of the living waking man. Specific heat is the total volume of the sun is two orders of magnitude smaller. With such a modest specific energy supplies “fuel” (hydrogen) is enough for a few billion years to maintain a fusion reaction.
Kernel – the only place in the sun, in which the energy and heat is obtained from a fusion reaction, the rest of the star is heated by this energy. All the energy of the nucleus sequentially passes through the layers, up to the photosphere, which is emitted in the form of sunlight, and the kinetic energy.
Above the nucleus, at distances of about 0.2-0.25 to 0.7 solar radii from the center, there is a zone of radiative transfer. In this zone, the energy transfer occurs mainly through the emission and absorption of photons. The direction of each individual photon is emitted by the plasma layer, does not depend on what photons are absorbed by the plasma, so it may or may not get into the next layer of the plasma in the radiative zone, and move back into the lower layers. Because of this period of time during which repeatedly re-radiated photon (originally emerged in the core) reaches the convective zone, can be measured in millions of years. The average time for the sun is 170 thousand years .
The temperature difference in the area range from 2 million to the surface up to 7 million to a depth . Thus in this area there are no macroscopic convective motion, which says that the adiabatic temperature gradient in it more than the gradient of radiative equilibrium.For comparison, the red dwarfs pressure can prevent the mixing of matter and the convection zone starts right from the nucleus. The density of matter in the area ranges from 0.2 (on the surface) to 20 (in depth) density of water .
Closer to the Sun’s surface temperature and the density of the substance is not enough for the complete transfer of energy by reradiation. Eddy mixing of the plasma and the energy transfer to the surface (photosphere) is accomplished mainly movements of the substance itself. On the one hand, the substance of the photosphere, the surface cools, sinks deep into the convection zone. On the other hand, the substance in the bottom of the radiation received from the area of radiation transport and rises to the top, and both processes are at a significant rate. This method of energy transfer is called convection, and the subsurface layer thickness of about 200 Suns 000 km, where it is happening – the convection zone. As we approach the surface temperature drops to an average of 5800 K, and the gas density to less than one thousandth the density of terrestrial air. 
According to current data, its role in the physics of solar processes is extremely high, as it is in it originate diverse movements of solar material. Thermals in the convective zone cause the surface granules (which are in fact vertices thermals) and supergranulation. The flow rate was an average of 1-2 km / s, and its maximum value reaches 6 km / s. The lifetime of the granules is 10-15 minutes, which is comparable with the period for which the gas can once go round granules. Consequently, the thermal convection in the area are in conditions dramatically different from those that contributed to the Benard cells . As movements in the area caused the effect of magnetic dynamo and therefore generates a magnetic field that has a complex structure.
Photosphere (the layer that emits light) forms the visible surface of the Sun. Its thickness corresponds to an optical thickness of approximately 2/3 units. In absolute terms, the photosphere reaches the thickness, according to various estimates, from 100 and 400 km . Comes from the photosphere bulk optical (visible) solar radiation, the radiation is from the deeper layers to it no longer comes. Temperature as it approaches the outer edge of the photosphere decreases from 6600 K to 4400 K . The effective temperature of the photosphere of a total of 5778 K . It can be calculated by the Stefan – Boltzmann, according to which the radiation power of a black body is directly proportional to the fourth power of the temperature of the body. Hydrogen under such conditions remains almost entirely in the neutral state. Photosphere forms a visible surface of the Sun, which are determined by the size of the Sun, the distance from the sun, etc. Since the gas in the photosphere is relatively sparse, the speed of rotation is much less than the speed of rotation of solids. The gas in the equatorial and polar regions, moves irregularly – on the equator it does turnover for 24 days at the poles – 30 days
Chromosphere (from al-Greek. Χρομα – color, σφαίρα – a ball, a sphere) – Sun’s outer shell thickness of about 2000 km, the surrounding photosphere. Origin of the name of this part of the solar atmosphere due to its reddish color, caused by the fact that in the visible spectrum of the chromosphere is dominated by red H-alpha emission line of hydrogen Balmer series. The upper boundary of the chromosphere has expressed a smooth surface of it are constant hot emissions, called spicules. The number of spicules observed at the same time, an average of 60-70 thousand  Because of this, at the end of XIX century Italian astronomer Secchi, watching the chromosphere of the telescope, compared it with the burning prairies). Chromospheric temperature increases with altitude from 4000 to 20 000 K (temperature greater than 10 000 K is relatively small).
The density of the chromosphere is small, so the brightness is insufficient to see in normal circumstances. But at the total solar eclipse, when the moon covers the bright photosphere, located above the chromosphere becomes visible and is red. It can also be observed at any time with the help of special narrow-band optical filters. In addition to the aforementioned H-alpha with wavelength 656.3 nm, the filter can also be configured on the line Ca II K (393,4 nm) and Ca II H (396,8 nm). The main chromospheric structures that are visible in these lines [:
chromospheric network covering the whole surface of the sun, consisting of lines surrounding the supergranulation cell sizes up to 30 thousand kilometers in diameter;
plages – bright cloud-formation, often confined to areas with strong magnetic fields – the active areas of the surrounding sun spots;
fibers and filaments (fibrils) – dark lines of varying widths and lengths, as plages, often found in active regions.
Corona – the last outer shell of the sun. The crown consists mainly of prominences and eruptions of energy, outgoing, and erupting into several hundreds or even more than a million miles in space, forming the solar wind. The average coronal temperature is from 1 000 000 to 2 000 000 K, and the maximum, in some areas – from 8 million to 20 million K . Despite the high temperatures, it is visible to the naked eye only during a total solar eclipse, as the density of matter in the corona is small, so small, and its brightness. Unusually intense heating of this layer is called, apparently, the effect of magnetic reconnection and the impact of the shock waves (see the coronal heating problem.) The shape of the crown varies depending on the phase of the solar cycle: during periods of peak activity, it is round, and at the minimum – stretched along the solar equator. Since the temperature of the corona is very large, it radiates intense ultraviolet and X-ray bands. This radiation does not penetrate the Earth’s atmosphere, but recently it became possible to study them with the spacecraft. The radiation in different regions of the corona is uneven. There are hot active and quiet region and coronal holes with a relatively low temperature of 600 000 K, of which space out the magnetic field lines. This (“open”) magnetic configuration allows the particles to freely leave the Sun, so the solar wind is emitted mainly from coronal holes.
The visible spectrum of the solar corona consists of three different components, called L, K and F components (or, respectively, L-crown, K-corona and the F-corona, another name for L-components – E-crown . K- component – a continuous spectrum of the corona. In the background to a height of 10.9 “from the visible edge of the Sun is visible emission L-component. Starting from a height of about 3 ‘(the angular diameter of the sun – about 30’) and can be seen above the Fraunhofer spectrum, the same as spectrum of the photosphere. It is F-component of the solar corona. At a height of 20 ‘F-component dominates the spectrum of the corona. height 9.10 “is taken as the border separating the inner from the outer crown. solar radiation with a wavelength of less than 20 nm, the full proceeds from the the Crown. This means that, for example, common images of the Sun at wavelengths 17.1 nm (171 Å), 19,3 nm (193 Å), 19,5 nm (195 Å), the solar corona is visible only with its elements and the chromosphere and photosphere – not visible. Two coronal holes, almost always exist in the north and south poles of the Sun, and the other, temporarily appearing on its visible surface, almost did not emit x-rays.
From the outer solar corona expires solar wind – a stream of ionized particles (mostly protons, electrons, and α-particles), which applies to the gradual decrease in density, to the limits of the heliosphere. The solar wind is divided into two components – the slow solar wind and the fast solar wind. Slow solar wind has a speed of about 400 km / s and a temperature of 1.4-1.6 x 106 K and the composition corresponds closely to the crown. Fast solar wind has a speed of about 750 km / s, temperature of 8.105 K, and the composition of a substance similar to the photosphere. Slow solar wind is twice as dense and less permanent than fast. Slow solar wind has a more complex structure with regions of turbulence .
On average, the sun radiates to the wind about 1.3 x 1036 particles per second. Hence – a total loss of mass of the sun (for this type of radiation) for the year is 3.2 · 10-14 solar masses. This is equivalent to a loss of mass equal to the Earth for 150 million years. Many natural phenomena on Earth are associated with disturbances in the solar wind, including geomagnetic storms and auroras.
The first direct measurements of the characteristics of solar wind were held in January 1959, the Soviet station “Luna-1” . The observations were made using a scintillation counter and a gas ionization detector . Three years later, the same measurements were carried out by American scientists using the station “Mariner-2” . In the late 1990s, using an ultraviolet coronal spectrometer (born Ultraviolet Coronal Spectrometer (UVCS)) on board the satellite SOHO observations were made of regions of the fast solar wind at the solar poles.
The magnetic field of the Sun
Since the solar plasma has a high electrical conductivity, it can generate electric currents and, as a consequence, the magnetic field. Directly observed in the solar photosphere, the magnetic field can be divided into two types, according to their scale.
The large-scale (global or global) magnetic field with characteristic dimensions comparable to the size of the Sun, has an average intensity at the photosphere of a few gauss. At the minimum of the solar cycle, it has about a dipole structure, with the field strength at the poles of the solar maximum. Then, as we approach the peak of the solar cycle, the field strength at the poles and gradually decrease after one or two years after the maximum of the cycle are equal to zero (the “reversal of the solar magnetic field”). In this phase of the general magnetic field of the Sun does not completely disappear, but its structure is not the dipole and quadrupole. After that, the intensity of solar dipole increases again, but he already has a different polarity. Thus, the full cycle of change of the total magnetic field of the sun, with the sign changes is equal to twice the length of the 11-year cycle of solar activity – about 22 years (the “law of Hale”).
Medium-and small-scale (local) field of the sun differ significantly larger field strengths and lower regularity. The most powerful magnetic field (up to several thousand gauss) are observed in groups of sunspots at the peak of the solar cycle. In this case, a typical situation where the magnetic field spots in the western (“head”) of the group, including the largest spot (so-called. “Group leader”) coincides with the polarity of the total magnetic field on the corresponding pole of the Sun («p- polarity “), and in the eastern (” tail “) part – the opposite of him (« f-polarity “). Thus, the magnetic fields of spots are usually bipolar or multipolar structure. In the photosphere also observed unipolar region of the magnetic field, which, in contrast to groups of sunspots, are closer to the poles and have a significantly lower magnetic field (a few gauss), but a large area and life span (up to several solar rotations).
According to modern ideas, shared most of the researchers, Sun’s magnetic field is generated at the bottom of the convection zone through the mechanism of convective hydromagnetic dynamo, and then emerges into the photosphere by the magnetic buoyancy. The same mechanism explains the 22-year cycles of solar magnetic field.
There are also some indications for primary (ie arose with the sun), or at least very long-lived magnetic field below the bottom of the convection zone – in the radiative zone and the core of the sun.
Solar activity and the solar cycle
Complex phenomena caused by the generation of high magnetic fields on the Sun, called the solar activity. These fields appear in the photosphere as sunspots and cause phenomena such as solar flares, generating streams of accelerated particles, changes in the levels of electromagnetic radiation in the different bands, coronal mass ejections, solar wind disturbances, variations of fluxes of galactic cosmic rays (Forbush effect) etc.
With solar activity variations are also related to geomagnetic activity (including magnetic storms) that result from reaching the Earth’s interplanetary disturbances caused, in turn, active phenomena on the Sun.
One of the most common indicators of solar activity is the Wolf number, associated with the number of sunspots on the visible hemisphere of the Sun. The overall level of solar activity varies with the characteristic period approximately equal to 11 years (the so-called “solar cycle” or “eleven-year cycle”). This period is maintained accurately and in XX century was closer to 10 years, and over the last 300 years ranged from about 7 to 17 years. Cycles of solar activity made to attribute sequential numbers starting from arbitrarily selected the first cycle, the maximum of which was in 1761. In 2000, there was a maximum of 23 of the first cycle of solar activity.
There are also variations in solar activity of longer duration. Thus, during the second half of XVII century, solar activity, and in particular, her eleven-year cycle were severely weakened (Maunder minimum). In the same period, a decrease in Europe average annual temperature (so-called. Little Ice Age), which might be due to the influence of solar activity on the Earth’s climate. There is also a view that global warming is to some extent due to the increase of the global level of solar activity during the second half of the XX century. However, the mechanisms of this effect is still not clear.
The largest group of sunspots on record occurred in April 1947 in the southern hemisphere of the Sun. Its maximum length is 300 000 km, maximum width – 145 000 km and a maximum area of more than 6000 parts per million square hemisphere (TIR) of the Sun , which is about 36 times that of Earth. The band was easily visible to the naked eye at sunset. According to the catalog of Pulkovo Observatory, this group (№ 87 of 1947) took place on the visible hemisphere of the Sun from the Earth, from 31 March to 14 April 1947, the maximum area was its 6761 discharge as the maximum area of the largest spot in the group – 5055 TIR number of spots the group reached 172 .
Since the magnetic activity of the Sun is subject to periodic changes, and with this change and its luminosity (see the solar cycle), it can be regarded as a variable star. In the years of maximum activity of the sun is brighter than in years minimum. The amplitude of the solar constant up to 0.1% (in absolute values is 1 W / m ², while the average value of the solar constant – 1361.5 W / m ²) .
Also, some researchers attribute to the class of low-level sun variable stars like BY Dragon . The surface of these stars stained (up to 30% of the total), and by the rotation of stars there are changes in their brightness. The Sun this variability is very weak.
The solar neutrino problem
Nuclear reactions in the core of the sun, lead to the formation of a large number of electron neutrinos. The measurement of the neutrino flux on Earth, which are constantly produced from the late 1960s showed that the number of solar electron neutrinos detected in approximately two to three times less than that predicted by the standard solar model, which describes the processes in the Sun. This mismatch between experiment and theory has been called “solar neutrino problem” and more than 30 years has been one of the mysteries of solar physics. The situation is complicated by the fact that neutrinos interact very weakly with matter, and the creation of a neutrino detector, which is capable enough to accurately measure the flux of neutrinos even such a power as emanating from the Sun – technically complex and expensive task (see neutrino astronomy).
Suggested two main ways to solve the solar neutrino problem. First, it was possible to modify the model of the sun so as to reduce the expected fusion activity (and hence temperature) in the nucleus, and therefore the flow of neutrinos emitted by the Sun. Second, it can be assumed that part of the electron neutrinos emitted by the core of the sun, the motion of the Earth into a non registered ordinary neutrino detectors of other generations (muon and tau neutrinos). Today it is clear that the right is likely to be the second path.
In order to have a transition of one type of neutrino to another – that is what is called the phenomenon of neutrino oscillations – neutrinos must have a non-zero mass. It is now established that this is indeed the case. In 2001, the Sudbury Neutrino Observatory (English) were directly recorded solar neutrinos of all three grades, and it was shown that their total flux is consistent with the standard solar model. However, only about a third of the Earth reaches the neutrino is electronic. This amount is consistent with the theory, which predicts a shift of electron neutrinos into neutrinos of another generation in vacuum (actually “neutrino oscillations”), and in the solar matter (“the Mikheev – Smirnov – Wolfenstein”). Thus, in the present solar neutrino problem seems to be solved.
Coronal heating problem
Above the visible surface of the Sun (photosphere), which has a temperature of about 6000 K, is the solar corona with a temperature over 1 million K can be shown that the direct flow of heat from the photosphere is not enough to lead to such a high temperature of the corona.
Assumed that the energy to heat the corona comes turbulent motions subphotospheric convection zone. In addition, for the transfer of energy into the corona proposed two mechanisms. First, it is heat wave – the sound and magnetohydrodynamic waves generated by the turbulent convection zone, subject to the crown, and there are scattered, and their energy is converted into thermal energy of the coronal plasma. An alternative mechanism – magnetic heating, in which magnetic energy is continuously generated by photospheric motions, released by the reconnection of the magnetic field in the form of large solar flares, or a large number of small flares .
At the moment it is unclear what type of wave provides an efficient mechanism for coronal heating. It can be shown that all the waves except Alfvén MHD are scattered or reflected before they reach the corona, the same dissipation of Alfven waves in the corona is difficult. Therefore, modern researchers have focused mainly on the mechanism of heating by solar flares. One of the possible candidates for the source of coronal heating – continuously occurring small-scale outbreaks , although the final clarity on this issue has not yet been reached.
Early observations of the Sun
From the earliest times humanity recognizes the important role of the sun – bright disk in the sky, carrying the light and heat. In many prehistoric and ancient cultures, the Sun was worshiped as a deity. The cult of the Sun occupied an important place in the religions of civilizations of Egypt, the Incas, the Aztecs. Many ancient monuments associated with the sun, for example, megaliths accurately mark the summer solstice position (one of the largest such megaliths are in-Nabta Playa (Egypt) and Stonehenge (England)), the pyramid at Chichen Itza (Mexico) are constructed in such a way the shadow of the earth slipped on a pyramid in the vernal and autumnal equinoxes, etc. The ancient Greek astronomers, observing the apparent annual motion of the sun along the ecliptic, the sun was considered one of the seven planets (from al-Greek. ἀστὴρ πλανήτης – wandering star). In some languages, the Sun, along with the planets, is dedicated to the week.
The development of modern scientific understanding
One of the first to attempt to look at the sun from the scientific point of view, the Greek philosopher Anaxagoras. He said that the sun – not the chariot of Helios, as taught Greek mythology, a giant, “is bigger than the Peloponnese,” a red-hot metal ball. For this heresy, he was imprisoned and sentenced to death, and was released only through the intervention of Pericles.
The idea that the Sun – is the center around which the planets are turning, expressed Aristarchus of Samos and ancient scientists (see heliocentric system of the world.) This theory was revived by Copernicus in the XVI century.
The first distance from the Earth to the sun trying to figure Aristarchus of Samos, by measuring the angle between the sun and the moon phase in the first or last quarter, and defining of a right triangle corresponding ratio of the distance from the Earth to the Moon to the distance from the Earth to the Sun.By Aristarchus, the distance to the sun 18 times longer than the distance to the moon. In fact, the distance to the Sun in 394 times the distance to the moon. But the distance to the moon in the antiquity it was determined very accurately Hipparchus, and he used the method proposed by Aristarchus of Samos (the other, of course, above).
Chinese astronomers for centuries, since the time of the Han Dynasty, observed sunspots. First spots were sketched in 1128 in the chronicle of John of Worcester. In 1610 begins the era of instrumental studies of the Sun. The invention of the telescope and its special varieties for observations of the Sun – helioscope – allowed Galileo, Thomas Herriot, Christoph Scheiner and other scientists to examine sunspots. Galileo, apparently, the first among the researchers found a part of the solar spots structure, in contrast to Scheiner, considering their passing before the sun the planets. This assumption allowed Galileo discovered the rotation of the sun and calculate its period. Priority open spots and their nature has been devoted more than ten years the debate between Galileo and Scheiner, however, most likely, the first observation and the first publication does not belong to any of them.
The first is more or less a reasonable estimate of the distance from Earth to the Sun parallax method were Giovanni Domenico Cassini and Jean Richer. In 1672, when Mars was in great opposition to the Earth, they measured the position of Mars at the same time in Paris and Cayenne – the administrative center of French Guiana. Observed parallax was 24. ” The results of these observations, it was found the distance from Earth to Mars, which was then converted to the distance from the Earth to the Sun – 140 million km.
At the beginning of XIX century, Father Pietro Angelo Secchi (Italian Pietro Angelo Secchi), the chief Vatican astronomer, initiated this line of research in astronomy, as spectroscopy, spreading sunlight into its component colors. It became clear that in this way we can study the stars, and found the Fraunhofer absorption lines in the solar spectrum. Thanks spectroscopy found a new element in the Sun, which was named in honor of helium Greek sun god Helios.
Remained unclear for a long time a source of solar energy. In 1848, Robert Mayer advanced meteorite hypothesis that the sun is heated by bombardment by meteorites. However, with so many meteorites strongly heated and the Earth would be, in addition, terrestrial geological strata would consist mainly of meteorites, and finally, the mass of the sun was to rise, and this would affect the movement of the planets. Therefore, in the second half of the XIX century, many researchers considered the most plausible theory, developed by Helmholtz (1853) and Lord Kelvin , who proposed that the sun is heated by the slow gravitational compression (the “mechanism of Kelvin – Helmholtz”). Based on this mechanism, the calculations estimated the maximum age of the sun at 20 million years, and the time at which the sun off – no more than 15 million . However, this hypothesis contradicts the geological data on the age of the rocks, which indicated a much higher figures. However, the Encyclopedia Britannica says the gravity model only allowed .
Only in the XX century was correct solution to this problem. Rutherford initially hypothesized that the source of internal energy of the sun is radioactive decay. In 1920, Sir Arthur Eddington proposed that the pressure and the temperature in the interior of the sun is so high that there can be a fusion reaction in which hydrogen nuclei (protons) fuse into helium-4 nucleus. Since the mass of the latter is less than the sum of the masses of four free protons, the part of the mass in this reaction is converted into the energy of the photons . That hydrogen is predominant in the composition of the Sun, confirmed in 1925, Cecilia Payne. Fusion theory was developed in the 1930s, astrophysicists Chandrasekhar and Hans Bethe. Bethe calculated in detail the two major fusion reactions, which are sources of solar energy. Finally, in 1957, a paper appeared Margaret Burbidge “Synthesis of elements in stars” in which it was shown that most of the elements in the universe was the result of nucleosynthesis in stars.
In 1905, George Ellery Hale (born George Ellery Hale) at the Mount Wilson Observatory installed the first solar telescope in the small observatory built, and began searching for the answer to the origin of sunspots, Galileo. George Hale discovered that sunspots are caused by the magnetic field, because it reduces the surface temperature. It is the magnetic field at the Sun’s surface from solar winds – the eruption of plasma of the solar corona on the hundreds of thousands of kilometers into space.