The sun is a typical star and is a giant ball of gas. By their physical characteristics the Sun — an average star of mass of about 2*1030 kg and a radius of 7*108 m.
The sun consists mainly of hydrogen (~70% by mass) and helium (~29%). (Hydrogen by number of atoms in 10 once more, than other elements.) The mass of the Sun in 330 000 times the mass of Earth, and a huge gravitational pull greatly compresses these gases. Calculating the amount of solar ball, it is possible to calculate, the average density of solar matter is 1,4*103 kg/m3, t. e. more the density of water. Towards the center the pressure of the overlying layers increases and the density of the gas increases, reaching the center of the Sun about 1,5*105 kg/m3, more than 10 times the density of lead.
The sun radiates into the world every second an enormous amount of energy. The source of this energy are thermonuclear reactions, which occur in the subsoil thereof. The temperature in the center of the Sun reaches 13*106 K and gradually decreases with distance from the center.
The transfer of energy from the interior of the Sun takes place mainly by radiation. The radiation of the inner layers is absorbed by overlying layers, which in turn by means of radiation energy is transferred to the next layers, and so on, to layer, radiation which breaks, finally, out, in outer space.
Layer, which is formed in the visible radiation of the Sun, called the photosphere, we see as the disk of the sun. The thickness of the photosphere is a few hundred kilometers, pressure order 0,1 ATM. The temperature of the inner layers of the photosphere is about 6000K to 4500K and decrease in its external layer. The photosphere is the lower atmosphere of the Sun. Above it there is the chromosphere, and the outer tenuous part of the atmosphere called crown (rice. 6.4). The gas in the chromosphere and the corona is very tenuous: in the upper chromosphere contains only about 1015 atoms/m3, and in the crown — by an order of magnitude less (compare with the Earth's atmosphere: pL=2,7*1025 molecules/m3).
Losing energy by radiation into the World environment, gas in the photosphere cools quickly, and in the layer, lying under the photosphere, occurs vertical mixing — convection. When observed through a telescope can be seen, the photosphere consists of numerous pellets small clouds of hot gas more, that rise from the depths, displacing the cooled gas, and in a few minutes apart, substituted new. Sometimes formed steady rising streams of hot gases, called torches. They are visible as brighter areas. From time to time appear in the photosphere dark spots, representing a colder region. By the way, the movement of these spots was detected rotation of the Sun.
Under the influence of powerful convective motions in the solar matter arise mechanical vibrations and waves are formed, similar to sound. As propagation of these waves into the upper atmosphere, where the gas is strongly attenuated, the amplitude of the (scope) vibrations of the particles of the gas increases to a few kilometers and greatly increase the speed of oscillatory motion of particles. However, such fluctuations can not long maintain the correct character, and undulations of extended regions of gas are divided into separate small randomly moving mass of gas. In the result at the expense of mechanical energy of waves greatly increases the average energy of random motion of gas particles, and the temperature in the chromosphere increases to tens of thousands of Kelvins, and in the crown to 106 To). Due to the very low density of matter the brightness of the corona is a million times less, than photosphere, and does not exceed the brightness of the moon. The crown is convenient to observe during a total solar Eclipse, when the Moon shuts from us the bright disk of the photosphere. The crown has a radiant structure, moreover, the length of the rays can be more than ten times the radius of the photosphere.
The kinetic energy of the gas particles in the corona is so great, many of them overcome the Sun's gravity and fly off into interplanetary space. The flow of these particles, moving at speeds of hundreds of km/s, call the solar wind. Note, what the solar wind, and light pressure causes the formation "comet's tail", which is always directed away from the Sun.