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The Sun1 - see at ground level You will notice that this...

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The Sun's electromagnetic spect rum The sun emits what is very close to a black body spectrum. The nearest black body equivalent would be the spectrum of 5900K, though if we look at the details there are some deviations from this: The outside curve is a black body radiator at 5900K. This is an especially good fit to the right- hand part of the sun's spectrum when seen from space. The left-hand side (shorter wavelengths than the peak) is better characterised by a slightly lower temperature - say around 5700. This is true down to around 300nm. Below that there is a fall-off which fit even cooler bodies, until we get to 140-200nm, when the energy rises well above the 5900K black-body level. We shall see this below.
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In the diagram above we also see the effect of the Earth's atmosphere. The inner curve is what we
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Unformatted text preview: see at ground level. You will notice that this cuts off some of the radiation at all wavelengths, but over the middle visible band - 400-800nm - most radiation gets through (fortunately for life at ground level!). There are big "vl!). There are big "valleys" of attenuation from 800-1300nm where water and Carbon Dioxide absorption have a large effect. Above 1300nm (1.3 microns) there are several frequency bands where the water and CO 2 absorption are so strong the radiation does not reach ground level at all. The radiation less than 200nm in wavelength (the EUV and XUV) is also stopped high in the atmosphere (again, fortunately for life on the ground!)....
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