Sun |
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| Our Sun |
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| The Sun is in 2/3 of the galactic center towards the edge, at a distance of 30 000 light years of the center. The Sun moves in a speed of 230 km/s around this galactic center during its revolution which it makes in 250 million years: since its birth, it made 18 times the tour of the Milky Way. Our thermonuclear power plant transforms in its nucleus, in a temperature of 15 million degrees, the hydrogen into helium and it since 5 billion years. The consumption of the Sun is 4 million tons of hydrogen per second (loss of mass). In the center of this thermonuclear power plant, radioactive substances, tritium and beryllium 7, circulate freely. |
Fortunately 700 000 km (beam of the Sun) of matter,
isolate them from the space global inter. Superficial layers appears a
powerful wind which propagates in the space. Subjected to these squalls,
comets are decorated with a tail showing the solar direction. The Earth
is not totally sheltered by its magnetic folding screen, the wind
infiltrates by polar cracks, to show us these magnificent auroras
borealis of white, green, red lights. |
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| Distance Earth Sun |
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Because of the ellipticity of the Earth's orbit, the distance Earth - Sun varies of 3,3 %. We often believe that it is during the winter of the north hemisphere, that the Sun is farthest of the Earth. But really, the seasonal temperatures are essentially influenced by the height of the Sun in the sky. During the winter of the north hemisphere, the inclination of the axis of rotation of the Earth makes that the Sun never rises very high. The Earth is in closer of the Sun in January and in most farther in July. |
This image allows to compare the relative size of the Sun when it
belongs in closer of the Earth, in January (to the left), in the one
that it presents when it is in most farther, in July (to the right). The
angular size of the Sun is strikingly weaker in July, when it is in most
farther. If the orbit of our planet around the sun was perfectly
circular, our star would seem to have always the same size. These two
images of the Sun were taken since Spain in 2006. |
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| Protuberances |
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The eruptive protuberances of the Sun are enormous geysers of solar matter which dash in hundreds of thousand kilometers in the space. The spatial satellite
Soho Thrown in 1995, the Soho program contributes to the
international scientific programs of the study of the relations
Earth-sun. Soho is led in association with Nasa, in charge of the launch
of the satellite, his control and the realization of several
instruments. The satellite was built in Toulouse by an European
industrial consortium led by the company Astrium, instruments were
supplied by the scientific community. More than 500 researchers of 20
different countries are so involved in this program. France so conceived
instruments EIT, Swan and Golf, and strongly contributed to the
realization of the experiments Sumer, CDS and Lasco. Although it was not
conceived in this objective, Soho became the most prolific discoverer of
comets of the history of the astronomy.
made ceaselessly by surprising discoveries. The satellite so
detected complex gaseous currents circulating under the solar surface
but also the shock waves and the permanent explosions in the solar
atmosphere. |
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Placed between the Sun and the Earth, Soho detects the signs of solar activity before they reach our planet. At the end of 2003, violent solar flares took place, pouring a stream of energy particles in the solar system. The instruments of Soho were able to observe this unprecedented phenomenon. By mapping the sky in the ultraviolet ray, the instrument Swan is notably capable of studying the activity on the opposite face of the Sun. |
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| The cycle of the Sun |
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The easy observation of sunspots allows to notice not only that the rotation of the sun on itself is made in 27 days but also that the activity of the warm and cold zones of the Sun respect a cycle. The solar cycle is the period during which the activity of the Sun varies from a maximum to the other one. Theoretically, the solar activity is adjusted by a cycle of an average period of 11,2 years but the duration can vary between 8 and 15 years. The cycle of 11 years was determined for the first time by the German astronomer Heinrich Schwabe by 1843. In 1849, the Swiss astronomer Johann Rudolf Wolf ( 1816-1893 ) establishes a method of calculation of the solar activity based on the number of spots. The cycles of Schwabe are numbered from the maximum of 1761. In 2003, the cycle n°23 is on the decline, the cycle n°24 will begin in 2012. The variations of the solar activity are translated on Earth, by fluctuations in the distribution of the waves radio. The most got range of frequencies covers the said diametric waves or the short waves which propagate at long distance. During these magnetic thunderstorms, the very strong ionization of the high layers of the |
atmosphere can perturb the communications with
satellites with the consequences that we can imagine for
telecommunications. Sunspots appear group in the warm photosphere (5800
K) there as a colder, dark zone (4500 K) surrounded with a clearer
region (4500 K in 5800 K) and are due to a local increase of the
magnetic field. These spots can reach dimensions of several tens of
thousand km. At the beginning of the solar cycle, spots appear rather to
high latitude in both hemispheres (the North and the South). Throughout
the cycle, spots are going to get closer to the equator till the
beginning of the following cycle. |
One of the enigma not resolved by the first polar
passage in 1994 and 1995 concerns the temperature of the poles of the
Sun. During its passages over the South Pole then over the North Pole,
for a period of minimum solar energy, the probe had measured the
temperatures of the big polar holes. Strangely, the temperature of the
polar hole the North was about 7 in 8 percent lower than that of south
polar hole (source: Solar Wind Ion Composition Spectrometer). |
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| The life of a star |
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| " The universe needed places denser than the galaxies, to reach the complexity, it invents then stars " Trinh Xuan Thuan. Pushed by the gravity, the small clouds of hydrogen and helium of the young galaxy, collapse and the density increases gradually. The gaseous balls ignite, it is the birth of stars as the Sun. The nuclear energy loosened in its |
balls, stop the gravitational collapse and a balance settles down between the pressure of the radiation and that of the gravity. The big stars live some million years, stars average as our Sun, exhaust their reserve of hydrogen only at the end of 9 billion years and the small stars will burn their fuel, 20 billion for years. When the hydrogen is consumed, the |
gravitational pressure gets over it, the density increases and the temperature reaches 100 million degrees. The nuclei of helium 4, produced by the combustion of the hydrogen, group together to form nuclei of carbon 12. The pressure of the radiation resumes vigor, the contraction stops, the star swells excessively, cools and becomes a red giant. |
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| Later |
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300 million years later, the combustion of the helium is ended, the heart of the red giant contracts again, for lack of a sufficient radiation. The temperature reaches then 500 million degrees, and it is now in the tour of the carbon to waste away for make the other elements |
always more complex, as the neon, the oxygen, the sodium, the magnesium, the aluminum, the silicon, the phosphor, the sulfur. These sequences are going to repeat many a time by accelerating and towards the end of its life, the heart of the star contains some iron, some cobalt |
And some nickel, result of the combustion of the silicon. In stars, real cosmic ovens, are going to be made, more and more heavy chemical elements necessary for the walking forward towards the complexity. |
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| The cycle proton-proton |
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In the stars of solar type, a suite of reactions called
" chain proton-proton " operates in several stages. |
(2 protons and 1 only neutron) and a photon; two of these unstable nuclei merge to lead to the very unstable beryllium 6 which splits at once to give finally the stable nucleus of helium 4 with formation of 2 protons. 6 protons are thus necessary so that a stable nucleus of helium can form, with restoration of 2 protons; the balance sheet is many 4 protons for a nucleus He4. |
Chains protons-protons require a temperature superior to 10 million degrees. A small quantity of helium 3 forms of the beryllium 7, which, during the other chains of reactions, leads to the lithium 7 or to the boron 8 giving of the beryllium 8 (with intense release of neutrinos): all these nuclei, very unstable, quickly transmute in helium 4. To know more about it, read " Life and death of stars " of Agnès Acker and Ariane Lançon |
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| The layers of the Sun |
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| The death of a star |
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The death of a star can be sweet or rapes, it depends on its mass. Below 1,4 times the mass of the Sun, the star goes out in the serenity, it will pass of the size of a red giant (approximately 50 million Km of beam), in that of the Earth (approximately 6000 km of beam). The star becomes a white dwarf. Between 1,4 and 5 times the mass of the Sun, its agony is much more violent. Its beam |
narrows until 10 Km. The final density is enormous, nuclei cannot resist and the heart of the star becomes a gigantic nucleus of neutrons. The collapse provokes a terrible explosion which is going to throw the superior layers of the star in the space and we shall see shining in the sky, a supernova. Above 5 times the mass of the Sun, the collapse is extremely violent. This one cannot be any |
more arrested. The heart of the star A black hole becomes. The violence of the collapse produces a gigantic explosion which throws the superior layers of the star in the space. As in the previous case a supernova is going to extend, on hundreds of billion Km, sowing the interstellar middle of heavy elements, made during the life of the star and during the explosion. |
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Related subjects |
category : stars |
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Stars |
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Astronomy - october 15th 2007 |
