trum at various altitudes above Earth occurs to varying degrees. Much infra-red radiation does not reach ground level because of absorption in the upper atmosphere by water, and some carbon dioxide and oxygen molecules that lie between the ground and about 15 km of altitude (the troposphere). Ozone (tri-oxygen) and di-oxygen in the stratosphere absorbs much of the ultra-violet radiation (hence the 'ozone layer' at about 30km). A side effect of the ozone layer is that molecules re-radiate the energy in a few wavelengths of the green, red, and infrared regions, causing 'airglow'.
             It is because of the limitations of Earth's atmosphere, that astronomers learnt the benefits of observing from beyond it. Placing telescopes and instruments of mountain tops-to avoid clouds, bad weather and turbulence-or using balloons or aircraft, are useful, but satellites are far more so. All electromagnetic radiation can be detected, unaffected by absorp
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