4-Earth_sun_geometry_2011

# 4-Earth_sun_geometry_2011 - 2)ThecausesoftheEarth seasons A...

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Solar Radiation and the Seasons  2) The causes of the Earth  2) The causes of the Earth  seasons seasons

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A few considerations about the Sun The Sun surface is extremely hot ~ 5800K The electromagnetic energy is not depleted as it propagates towards the earth However as it moves away from the sun it is distributed over a greater area, which reduces its intensity (that is, the intensity of the solar radiation is less over Earth than it is over Mercury, for instance)
From Stefan-Boltzman Law E =σ T 4 (w/m 2 ) = The total solar emission= E x Sun area = E x 4πR 2 sun Where R sun = 6.955x10 8 m Total solar emission= 3.865 x 10 26 W E=6.4x10 E=6.4x10 7 Watts Watts per per m m 2 In other words, to know the In other words, to know the total solar emission we need to total solar emission we need to calculate E for the entire sun!!! calculate E for the entire sun!!!

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Imagine a sphere completely surrounding the Sun whose radius is equal the mean distance Earth- Sun = 1.5x10 11 m As the distance from the Sun increases the intensity of the radiation decreases in the proportion of the distance squared (the inverse square law) The incoming radiation = 2 2 11 26 / 1367 ) 10 5 . 1 ( 4 10 865 . 3 m W m x W x = π SOLAR CONSTANT SOLAR CONSTANT
FOR THE SAKE OF COMPARISON The solar constant for The solar constant for Mars (2.25x10 Mars (2.25x10 11 11 m from m from the Sun) = 608 W/m the Sun) = 608 W/m 2 For Earth = 1367 W/m For Earth = 1367 W/m 2

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Causes of Earth’s Season interesting sites with movies: http://astro.unl.edu/naap/motion1/animations/seasons_ecliptic.swf http://www.youtube.com/watch?v=DuiQvPLWziQ Earth’s orbit around the Sun is not perfectly circular but is an ellipse. Earth is nearest to the Sun (perihelion) on about January 4 and farthest away (aphelion) on July 4. These different represent only about 3% in terms of distance and 7% in terms of changes in the intensity of radiation . THESE DIFFERENCES DO NOT CAUSE SEASONS ON
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4-Earth_sun_geometry_2011 - 2)ThecausesoftheEarth seasons A...

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