In: Physics
Earth's atmosphere acts as an impenetrable barrier to all the elctromagnetic waves except radio and visible waves. The atmosphere of the earth absorbs most of the wavelengths, shorter than ultraviolet and most of the wavelengths between infrared and microwaves. Very large wavelength of radio waves are also absorbed by the ionosphere of the Earth's atmosphere but short to medium range wavelengths of radio waves are penetrable to the atmosphere, this range of radio waves which are penetrable to the atmosphere is known as radio window. The radio window start point is 5 MHz of frquency and end point is 30 GHz. The lower frequency end of the radio window is due to radio signals which are reflected back into space by the inosphere. The upper frequency end of the radio window is caused by the absorption of the radio waves by water vapor and carbon dioxide in the atmosphere. Therefore if the atmospheric conditions changes. the radio window expands or shrinks.