The Sun is a star around which the Earth turns.

It has an approximate diameter of 1,400,000 km and a mass of 1.99 × 1033 g.

The Sun revolves around itself. However, since it is constituted by a large mass of gases, the different regions do not rotate in solidarity, but they do so at different speeds, which depend on latitude.

The Sun, and with it the entire solar system, moves towards a point in the firmament located in the constellation of Hercules at a speed of about 19 km / s. This is because the Sun has a movement of translation around the galactic center, like all the stars of the Galaxy, whose period is 200 million years.

The Sun is formed by a certain number of concentric layers, but the only ones that can be directly observed are the external ones, which are called the photosphere, chromosphere and corona, respectively, and constitute the so-called solar atmosphere. Each of these layers has distinctive properties that are its own. The transition of the properties of one layer to those of the next does not take place in a brusque way, but gradually.

The Sun is directly or indirectly responsible for the vast majority of the planet's energy sources. In addition to having direct importance in photovoltaic solar energy and solar thermal energy, it has an influence on other renewable energies such as wind energy. In the case of wind energy, the sun is responsible for heating large amounts of mass that, when changing density, move generating a space that will occupy another mass of cold air. This mass movement is the wind.

In the case of fossil energy that comes from fossil fuels, the Sun also has its responsibility. Fossil fuels such as coal or oil have been generated from organic compounds that were generated by solar radiation through photosynthesis. Despite having its origin in the Sun, this type of energy is considered non-renewable because the process of transformation into fossil fuels lasts millions of years.

Model of the internal structure of the Sun

Layers of the Sun - Photosphere, chromosphere, corona Fotosfera, the innermost layer of the Sun

The photosphere is the innermost layer and is responsible for almost all of the visible light that the Sun emits into space. On its innermost side, it borders on the convective region of the Sun, and on its outermost side, with the chromosphere.

The width of the photosphere is approximately 400 km, and the temperature decreases from a value of 7,500 K, in the most internal regions, to a value of 4,700 K, to the most external. The average pressure of the photosphere is only a few hundredths of the atmospheric pressure at sea level, while the density is only one ten-millionth of the density of Earth's atmosphere at sea level.

Observed in the telescope, the photosphere does not present a uniform appearance, but seems to be constituted by small granular cells, called rice grains, which appear separated by darker regions in which the temperature is lower.

Chromosphere, intermediate layer of the Sun

The chromosphere is the middle region of the solar atmosphere, and during the eclipses of the Sun, in the moments before the phase of fullness, it appears as a very fine arc of reddish color, which surrounds the eclipsed disk of the Sun. normal, that is, when there is no eclipse, it is not possible to observe the chromosphere so that the light from the photosphere attenuates its brightness, much weaker.

It is assumed that the chromosphere has a width of 2,000 to 3,000 km, but its upper end is covered by a forest of luminous gas springs, called spicules, so it is difficult to determine exactly the true dimensions. The density of the chromosphere decreases from the innermost to the outermost regions, but the temperature increases, at the same time, from 4,500 K to 100,000 K.

Crown, outer layer of the Sun

The crown is the outermost region of the solar atmosphere, and during the total eclipses it appears as a whitish halo that surrounds the eclipsed disk of the Sun. Its width is a few million kilometers, but the total luminosity is only equivalent to half the luminosity of the full moon. Analogously to the chromosphere, its vision is not possible outside the total eclipses, because the powerful luminosity of the neighboring photosphere masks the presence. The density of matter at the base of the crown is 109 atoms / cm2, which is equivalent to 10-10 times the density of the Earth's atmosphere at sea level.

The crown's temperature generally fluctuates around one million Kelvin, but in some of its regions it can be much higher. For a long time the cause of these temperatures has been a mystery, but nowadays it is believed that shock waves, caused by certain convective currents that occur in the photosphere, cause the warming of the corona and probably also of the chromosphere.

For the study of these two solar regions, the coronagraph is used. When analyzing the sunlight with a spectrometer, a continuous emission spectrum is obtained, on which numerous dark emission lines, said by Fraunhofer, overlap. The continuous component of the spectrum originates in the photosphere, and especially in its more superficial regions.

Indeed, in the photosphere there is at all times a dynamic balance between the rate of creation of negative hydrogen ions and the rate of destruction of these same ions, so that there is always a negative ion of hydrogen for every million atoms of hydrogen. hydrogen. The formation of these ions takes place by means of the absorption of photons that come from the interior of the Sun, while their destruction is accompanied by the emission of photons towards the outside of the Sun, which constitute the almost totality of the visible component of the Sun. solar radiation.

It is necessary, however, to establish three hypotheses concerning the solar photosphere. According to the first, the photosphere must be in hydrostatic equilibrium; the second assumes that it must also be in thermal equilibrium; and, according to the third, between its chemical components it is necessary that there be at least 90% hydrogen.

On the other hand, the absorption spectrum of the Sun occurs due to the presence, in the outer layers of the solar atmosphere, of atoms capable of absorbing photons of certain well-determined wavelengths; therefore, some radiation from the interior of the photosphere is selectively absorbed, which gives rise to the corresponding dark lines of the spectrum.

From these it has been possible to determine the chemical composition of the outer regions of the Sun. It has been seen that hydrogen and helium together constitute 96 to 99% of the photosphere, and that the rest is constituted by the others chemical elements, of which about 60 have now been identified. The existence of some 18 types of molecules in the coldest regions of the solar surface has also been detected.

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Last review: November 9, 2016