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Calculation To calculate the amount of sunlight reaching the ground nike juvenate herren schwarz , both the elliptical orbit of the Earth and the attenuation by the Earth's atmosphere have to be taken into account. The extraterrestrial solar illuminance (Eext), corrected for the elliptical orbit by using the day number of the year (dn), is: where dn=1 on January 1; dn=2 on January 2; dn=32 on February 1, etc. In this formula dn-3 is used, because in modern times Earth's perihelion, the closest approach to the Sun and therefore the maximum Eext, occurs around January 3 each year. The solar illuminance constant (Esc), is equal to 128103 lx. The direct normal illuminance (Edn), corrected for the attenuating effects of the atmosphere is given by: where c is the atmospheric extinction coefficient and m is the relative optical airmass. Solar constant A 1903 Langley bolograph with an erroneous solar constant of 2.54 caloriesminutesquare centimeter. Solar irradiance spectrum at top of atmosphere, on a linear scale and plotted against wavenumber. The solar constant, a measure of flux, is the amount of incoming solar electromagnetic radiation per unit area that would be incident on a plane perpendicular to the rays nike juvenate kaufen , at a distance of one astronomical unit (AU) (roughly the mean distance from the Sun to the Earth). When solar irradiance is measured on the outer surface of Earth's atmosphere, the measurements can be adjusted using the inverse square law to infer the magnitude of solar irradiance at one AU and deduce the solar constant. The solar constant includes all types of solar radiation, not just the visible light. It is measured by satellite to be roughly 1.366 kilowatts per square meter (kWm). The actual direct solar irradiance at the top of the atmosphere fluctuates by about 6.9% during a year (from 1.412 kWm in early January to 1.321 kWm in early July) due to the Earth's varying distance from the Sun, and typically by much less than one part per thousand from day to day. Thus, for the whole Earth (which has a cross section of 127,400,000 km), the power is 1.7401017 W, plus or minus 3.5%. The solar constant does not remain constant over long periods of time (see Solar variation), but over a year varies much less than the variation of direct solar irradiance at the top of the atmosphere arising from the ellipticity of the Earth's orbit. The approximate average value cited, 1.366 kWm, is equivalent to 1.96 calories per minute per square centimeter nike blazer suede schwarz , or 1.96 langleys (Ly) per minute. The Earth receives a total amount of radiation determined by its cross section (RE), but as it rotates this energy is distributed across the entire surface area (4RE). Hence the average incoming solar radiation, taking into account the angle at which the rays strike and that at any one moment half the planet does not receive any solar radiation, is one-fourth the solar constant (approximately 342 Wm). At any given moment, the amount of solar radiation received at a location on the Earth's surface depends on the state of the atmosphere and the location's latitude. The solar constant includes all wavelengths of solar electromagnetic radiation, not just the visible light (see Electromagnetic spectrum). It is linked to the apparent magnitude of the Sun, 26.8, in that the solar constant and the magnitude of the Sun are two methods of describing the apparent brightness of the Sun, though the magnitude is based on the Sun's visual output only. In 1884, Samuel Pierpont Langley attempted to estimate the solar constant from Mount Whitney in California. By taking readings at different times of day, he attempted to remove effects due to atmospheric absorption. However, the value he obtained nike blazer suede rot , 2.903 kWm, was still too great. Between 1902 and 1957, measurements by Charles Greeley Abbot and others at various high-altitude sites found values between 1.322 and 1.465 kWm. Abbott proved that one of Langley's corrections was erroneously applied. His results varied between 1.89 and 2.22 calories (1.318 to 1.548 kWm), a variation that appeared to be due to the Sun and not the Earth's atmosphere. The angular diameter of the Earth as seen from the Sun is approximately 111,000 radians, meaning the solid angle of the Earth as seen from the Sun is approximately 1140,000,000 of a steradian. Thus the Sun emits about two billion times the amount of radiation that is caught by Earth, in other words about 3.861026 watts. Sunlight intensity in the Solar System Different bodies of the Solar System receive light of an intensity inversely proportional to the square of their distance from Sun. A rough table comparing the amount of light received by each planet on the Solar System follows (from data in ): Planet Perihelion - Aphelion distance (AU) Solar radiation maximum and minimum (Wm) Mercury 0.3075 0.4667 14,446 6,272 Venus 0.7184 0.7282 2,647 2 nike liberty 2011 kaufen ,576 Earth 0.9833 1.017 1,413 1,321 Mars 1.382 1.666 715 492 Jupiter 4.950 5.458 55.8 45.9 Saturn 9.048 10.12 16.7 13.4 Uranus 18.38 20.08 4.04 3.39 Neptune 29.77 30.44 1.54 1.47 The actual brightness of sunlight that would be observed at the surface depends also on the presence and composition of an atmosphere. For example Venus' thick atmosphere reflects more than 60% of the solar light it receives. The actual illumination of the surface is about 14,000 lux, comparable to that on Earth "in the daytime with overcast clouds". Sunlight on Mars would be more or less like daylight on Earth wearing sunglasses, and as can be seen in the pictures taken by the rovers, there is enough diffuse sky radiation that shadows would not seem particularly dark. Thus it would give perceptions and "feel" very much like Earth daylight. For comparison purposes, sunlight on Saturn is slightly brighter than Earth sunlight at the average sunset or sunrise (see daylight for comparison table). Even on Pluto the sunlight would still be bri? The .
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