by yudaica2013 ·

Main article: The photosphere is the visible where visible light is emitted from the Sun’s photosphere is considered the “surface” solar and viewed through a telescope shows bright granules formed by projected on a darker background. Because of the turmoil of our atmosphere, these granules seem to be always in turmoil. Since the Sun is gaseous, its photosphere is somewhat transparent: it can be observed to a depth of several hundred miles before turning completely opaque. It is generally acknowledged that the solar photosphere is about 100 or 200 km depth. Schematic of the ring structure of a solar flare and its origin caused by the deformation of the electromagnetic field lines. Although the edge or limb of the Sun is quite clear in a photograph or image projected with a solar telescope, is easily seen that the solar disk brightness decreases towards the edge.This phenomenon of the center to limb darkening arises because the Sun is a gaseous body with a temperature that decreases with distance from the center. The light seen in the center comes in most of the lower layers of the photosphere, hotter and therefore brighter. Looking toward the limbus, the visual direction of the observer is almost tangential to the edge of the solar disk as radiation comes mainly from the upper layers of the photosphere, emitting colder and with less intensity than the deep layers at the base of the photosphere. A photon takes an average of 10 days after is a merger of two hydrogen atoms to pass through the radiant zone and a month to travel the 200 000 km of the convective zone, and use only about 8 minutes to cross the distance separating Earth from the Sun is not the photons travel faster now, but outside the sun the way of the photons is hampered by the constant changes, shocks, twists and turbulence experienced in the inside the sunThe bright granules in the photosphere are often hexagonal in shape and are separated by thin dark lines. The granules are evidence of the bubbling convective motion of hot gases in the outdoor sun Indeed, the photosphere is a continuous mass of boiling in which convective cells are seen as granules in motion with a lifetime is only about nine minutes. The average diameter of individual granules is from about 700 to 1000 km and are particularly noticeable during periods of minimum solar activity. There are also turbulent motions on a larger scale, the “supergranulation, with typical diameters of about 35 000 km. Each supergranulation contains hundreds of individual granules and survives between 12 to 20 hours. It was Richard Christopher Carrington (1826-1875), brewer and amateur astronomer, first observed photospheric granulation in the nineteenth century.In 1896 Frenchman Pierre Jules Cesar Janssen (1824-1907) was able to photograph for the first time the photospheric granulation. A detailed picture of a group of sunspots observed in the visible. The umbra and penumbra are clearly discernible and the solar granulation. The most obvious sign of activity in the photosphere are sunspots. In ancient times the sun was regarded as a divine fire and therefore perfect and infallible. Just as it was known that the bright face of the Sun was at times clouded with dark spots, but figured it was due to objects passing in the space between the Sun and Earth. When Galileo (1564-1642) built the first astronomical telescope, giving rise to a new stage in the study of the Universe, made the following statement, “Repeated observations have convinced me, that these spots are substances in the Sun’s surface, in the produced continuously and which also dissolve, some sooner and others later. “A typical sunspot is a dark central region, called the “umbra”, surrounded by a “penumbra” clearer. A single spot may reach up to 12 000 km (almost as large as the diameter of Earth), but a group of spots can reach 120 000 km long and sometimes even more. The penumbra consists of a structure of bright and dark filaments that extend more or less radially from the umbra. Both (umbra and penumbra) appear dark by contrast with the photosphere, simply because they are cooler than the average temperature of the photosphere. Thus, the umbra has a temperature of 4000 K, while the penumbra reaches 5600 K, lower than both the 6000 K with the granules of the photosphere.For the Stefan-Boltzmann law, where the total energy radiated by a black body (like a star) is proportional to the fourth power of its effective temperature (E T4, where 5.67051 10-8 W / m2 K4), the umbra emits approximately 32 of the light emitted by an equal area of the photosphere and the penumbra similarly has a brightness of 71 of the photosphere.

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