Sun Wallpapers

Sun - photo wallpapers: The Sun is the star at the center of the Solar System. The Earth and other matter (including other planets, asteroids, meteoroids, comets and dust) orbit the Sun, which by itself accounts for about 99.8% of the solar system's mass. Energy from the Sun—in the form of sunlight—supports almost all life on Earth via photosynthesis, and drives the Earth's climate and weather. The Sun is composed of hydrogen(about 74% of its mass, or 92% of its volume), helium (about 25% of mass, 7% of volume), and trace quantities of other elements. The Sun has a spectral class of G2V. G2 implies that it has a surface temperature of approximately 5,500 K, giving it a white color which, because of atmospheric scattering, appears yellow as seen from the surface of the Earth. This is a subtractive effect, as the preferential scattering of blue photons (causing the sky color) removes enough blue light to leave a residual reddishness that is perceived as yellow. Its spectrum contains lines of ionized and neutral metals as well as very weak hydrogen lines. The V (Roman five) suffix indicates that the Sun, like most stars, is a main sequence star. This means that it generates its energy by nuclear fusion of hydrogen nuclei into helium and is in a state of hydrostatic balance, neither contracting nor expanding over time. There are more than 100 million G2 class stars in our galaxy. Because of logarithmic size distribution, the Sun is actually brighter than 85% of the stars in the galaxy, most of which are red dwarfs. The Sun orbits the center of the Milky Way galaxy at a distance of approximately 26,000 light-years from the galactic center, completing one revolution in about 225–250 million years. The orbital speed is 217 km/s, equivalent to one light-year every 1,400 years, and one AU every 8 days.[br]While the Sun is an averaged-sized star, it contains approximately 99% of the total mass of the solar system. The Sun is a near-perfect sphere, with an oblateness estimated at about 9 millionths,[7] which means that its polar diameter differs from its equatorial diameter by only 10 km. As the Sun exists in a plasmatic state and is not solid, it undergoes differential rotation as it spins on its axis (i.e. it rotates faster at the equator than at the poles). The period of this actual rotation is approximately 25 days at the equator and 35 days at the poles. However, due to our constantly changing vantage point from the Earth as it orbits the sun, the apparent rotation of the sun at its equator is about 28 days. The centrifugal effect of this slow rotation is 18 million times weaker than the surface gravity at the Sun's equator. Also, the tidal effect from the planets do not significantly affect the shape of the Sun. The Sun does not have a definite boundary as rocky planets do; in its outer parts the density of its gases drops approximately exponentially with increasing distance from the center of the Sun. Nevertheless, the Sun has a well-defined interior structure, described below. The Sun's radius is measured from its center to the edge of the photosphere. This is simply the layer above which the gases are too cool or too thin to radiate a significant amount of light; the photosphere is the surface most readily visible to the naked eye. Most of the Sun's mass lies within about 0.7 radii of the center. The solar interior is not directly observable, and the Sun itself is opaque to electromagnetic radiation. However, just as seismology uses waves generated by earthquakes to reveal the interior structure of the Earth, the discipline of helioseismology makes use of pressure waves (infrasound) traversing the Sun's interior to measure and visualize the Sun's inner structure. Computer modeling of the Sun is also used as a theoretical tool to investigate its deeper layers.[br]

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Sun Wallpapers @ Mega Wallpapers (08 Edition)
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