Data from Wikipedia and NASA (C)
Star centers of our solar system; round to it rotate the planets, comets, asteroids and minor bodies likee meteoroida and powder.
Since the antiquity has been attempted explanations on the structure and composition of the sun. Greek philosopher Anassagora thought that it was a great sphere of inflamed metal, while Eratostene was the first one to calculate with precision the distance of the Earth from the Sun, in III century a.C., approximately 149 million kilometers, value much neighbor to that one modern. Copernico was the first one to put it to the center of the solar system in 16° the century, while Galileo with the first observations with the telescope discovering the solar spots. Isaac Netwon discovered its spectra but it studied Fraunhofer later on, while William Herschel discovered the infrared radiation. Lord Kelvin proposed that the sun was liquid and in cooling, and that it emitted its last inner heat. An other wrong hypothesis was the meteoric hypothesis on its formation. Only Rutheford in the 1904 began to propose a mechanism of radioactive decay like source of inner energy of heat. After the discovery of the relation between mass and energy of Einstein, Arthur Eddington proposed the idea of fusion reaction nuclear to its inside. The idea was studied from the physicists Chandrasekar and Bethe.
The sun has a inner temperature of 15 million °C and a density 1,50 g/cm³ maintained by means of the fusion reactions proton-proton of the hydrogen nuclei); every second 600.000.000 tons of hydrogen are transformed in 595.500.000 tons of helium. The lacking 4.500.000 tons hydrogen transform directly in energy second the equation of Einstein E=mc². The energy generated every second is equal to 405 x 1024 Joule, than expressed in watt-hour TWh (is equivalent to 112.500.000.000 for comparison the world-wide production of electric power in 2005 has been of 17.907 TWh).
The Sun is a star of main
sequence of spectral type G2 (a yellow dwarf). A star of G2 type, before
exausting all the its fuel completely, has a life of approximately 10 billions
of years, and currently the sun is to half of its vital cycle. The energy generated
is released initially through gamma rays and X, but during the emission towards
the outside it is continuously absorbed and released from surrounding atoms.
The result is that its frequency is lowered, and becomes therefore a
electromagnetic radiation more lowland. The passage of the energy from the
nucleus to the surface of the sun employs also 10 million years. To the end by
means of its emission the sun appears to us like a body to approximately
The nucleus is the inner zone of the Sun, where happen the thermonuclear reactions of fusion of hydrogen. The temperature is of the order of 15 million kelvin, the density is of approximately 160 g/cm³ and the pressure around to 500 billions of atmospheres. It is hidden to the direct observation. The information on its state come from the eliosismologia, that it takes advantage of the vibrations of the Sun, and from the emitted analysis of the neutrini from the fusion reactions. Other data as the production of energy total and the chemical composition of the surface allow to define the theoretical models. To these temperatures the hydrogen atoms of the nucleus separate in protons and electrons. The thermal energy is therefore high that when protons met met accidentally, gains the electrical repulsion electrical between same charges and they join to form a helium nucleus. Every second 594 million tons of hydrogen are converted. Therefore the sun is lightened every second of 4 million tons. Its total mass is enough large because, also after 10 billions of years of active life, its mass is reduced only imperceptibly. The energy freed from the fusion nuclear is introduced initially under photon shape. But they do not make much road interacting with other atoms. Once caught up the surface of the Sun they travel in the interplanetary space. The neutrini, other by-product of the fusion nuclear reactions, passes instead through the matter, and exits from the Sun online straight. A smallest part is intercepted from the little detectors of neutrini in activity on the planet. To the conditions enforced in the center of the Sun the medium proton must wait for 13 billions of years before melting with others three and forming a helium nucleus. As the time passes to the probability of the reactions it increases. The solar brightness increases slowly therefore, that it has induced some theorists to assume that between 500 million or a billion years the Sun will be too much warm in order to concur the life on the Earth. This increase is independent from the stellar evolution to which the Sun will go encounter, and that it will carry it between approximately 5 billions of years transforming itself in a giant red. The solar nucleus will become still more concentrated warmth than today: the fusion of helium, typical of the red giants, demands hundred of million degrees.
Situated to the outside of the nucleus, it absorbs the produced energy and it transmits for radiation to the superior layer. Pressure and temperature are still enough elevated to maintain the matter in state of plasma.
Situated to the outside of
the radiativa zone, transports the energy towards the outside by means of
convettivi motions. The gas that composes this zone moves, schematically, like
the water of a pot in boiling. It has a thickness of approximately
The fotosfera is the
superficial layer of the Sun, that is the zone of emission of the visible
light, is thick approximately
The cromosfera is the superior
layer respect the fotosfera. It is transparent, visible only with special
filters or during the totals eclipsess of Sun. This layer is interested from
various emissivi phenomena like spicule and the solar swells. It is thick
the solar corona is the more external part of the solar atmosphere, it does not have defined limits and it extends for tens million km. It is constituted from particles of ionized gases (hydrogen) and vapors from the below layers of the solar atmosphere. The temperature is much elevating (more than a million kelvin), superior to the fotosfera and the gas is a lot rarefied being in the state of plasma. Moreover the solar corona can be the solar wind for the entire solar system . It produces millionth of the visible light. The crown is separated from the fotosfera from the cromosfera. The exact mechanism of heating is a topic of scientific debate, but the main hypotheses include the induction of the solar magnetic field and the waves of sonic pressure (the last possibility are less probable now that has discovered the presence of crowns in primordiali stars). The crown is dispersed from the solar wind in its extremities. The crown is not uniform distributed around the surface: during the periods of quiet approximately it is confined in the equatorial regions, with "holes" in the polar regions, while during the periods of solar activity it is distributed around the Equator and to the poles and is mainly present in the areas of activity of the solar spots. Transienti the "transienti" of the crown are enormous amounts of material of the crown that travel more than million than km/h, and containing approximately 10 times the energy of flare that it provokes them. Some greater expulsions can emit hundred of million tons of matter in the space: when they catch up the Earth can damage the satellites and disturb the telecommunicationses.
A solar spot is a region of
the fotosfera characterized from a smaller temperature of the surrounding
atmosphere and from strong magnetic activity. Also if the solar spots are
extremely luminous, because they have a temperature of approximately 5000
kelvin, the contrast with the surrounding regions, still more luminous thanks
to a temperature of 6000 kelvin them renders clearly visible like dark spots.
If they were observable isolatedly they would be more luminous than one filament
lamp. The number of solar spots is correlated with the intensity of the solar radiation.
During the Minimum of Maunder they nearly disappeared, and the Earth in the
same period was cooled off in consisting way. The correlation between the two
events is object of arguments in the scientific community. Observation of the
solar spots : the first probable references to the solar spots are those of the
Chinese astronomers of the first millenium
The plasma and the electric particles that form the Sun generate a powerful magnetic field, connected to many solar phenomena like the spots and the solar eruptions. The layers of eliosferiche currents extend until the external edges of the solar system, and derive from the interaction of the solar magnetic field with interplanetary plasma. The Sun rotates to the Equator (approximately 25 days) regarding the greater latitudes (approximately 35 days close to the poles). This differentiates rotations them to the various latitudes of the Sun provokes to the twisting of the lines of the magnetic field and the consequent formation of solar spots and solar swells.
The solar wind is a
particle current emitted from the solar atmosphere. The solar wind is one
particle current (more than other protons with high energy, ~500 keV) emitted
from the solar atmosphere. Also the other stars show the same phenomenon, and
it is spoken therefore about stellar wind, or also of loss of mass. In 50 years
' a German scientist of name Ludwig Biermann studied comets, and the fact that
their tail always headed in opposite direction to the Sun. Biermann postulated
that this happened because the Sun emitted a constant particle flow that pushed
far away the tail of the comet. Eugene Parker understood that the flow of heat
from the sun in the model of Chapman and the tail of the comet tip via from the
sun in the hypothesis of Biermann had to be the result of the same phenomenon.
Since the gravity force is weakened with the distance from the sun, the
external solar corona escapes in the interstellar space. In the solar system,
the composition of this wind is identical to the crown of the Sun: 73% hydrogen
and 25% helium, with the rest formed from traces, and heavy are ionized. Close
to the Earth, the speed of the varied solar wind varied from
The first satellites plan to observe the Sun were Pioneer 5, 6, 7, 8 and 9 of NASA, launch between 1959 and 1968. These probes carried out the first measures detailed of the solar wind and the magnetic field. In years ' 70 operated the probes Helios 1 and Skylab. They came observed the first emissions of mass and the holes of the solar corona. NASA launch in 1980 the Solar Maximum Mission, constituted from a probe planned in order to observe the ultraviolet radiations, gamma rays and X rays coming from the solar flare during a period of high activity. The Japanese satellite Yohkoh came launch in 1991 and observed solar flare to the wavelengths of i X rays. The collected data allowed to identify various types of flare and demonstrated that the solar corona, also in the various periods from those of maximum activity, is more active and dynamics than how much was not supposed. The Ulysses probe came instead planned in order to study the polar regions; it came launch and directed so to go away from the ecliptical plan. Make observations of the solar wind and the magnetic field strength. The Genesis mission executed test on the solar wind and was planned for having a direct measure of the composition of the solar material