<P> To prevent interference between different users, the artificial generation and use of radio waves is strictly regulated by law, coordinated by an international body called the International Telecommunications Union (ITU), which defines radio waves as "electromagnetic waves of frequencies arbitrarily lower than 3 000 GHz, propagated in space without artificial guide". The radio spectrum is divided into a number of radio bands on the basis of frequency, allocated to different uses . </P> <P> Radio waves were first predicted by mathematical work done in 1867 by Scottish mathematical physicist James Clerk Maxwell . Maxwell noticed wavelike properties of light and similarities in electrical and magnetic observations . His mathematical theory, now called Maxwell's equations, described light waves and radio waves as waves of electromagnetism that travel in space, radiated by a charged particle as it undergoes acceleration . In 1887, Heinrich Hertz demonstrated the reality of Maxwell's electromagnetic waves by experimentally generating radio waves in his laboratory, showing that they exhibited the same wave properties as light: standing waves, refraction, diffraction, and polarization . Radio waves, originally called "Hertzian waves", were first used for communication in the mid 1890s by Guglielmo Marconi, who developed the first practical radio transmitters and receivers . The modern term "radio wave" replaced the original name "Hertzian wave" around 1912 . </P> <P> Radio waves in vacuum travel at the speed of light . When passing through a material medium, they are slowed according to that object's permeability and permittivity . Air is thin enough that in the Earth's atmosphere radio waves travel very close to the speed of light . </P> <P> The wavelength is the distance from one peak of the wave's electric field (wave's peak / crest) to the next, and is inversely proportional to the frequency of the wave . The distance a radio wave travels in one second, in a vacuum, is 299,792,458 meters (983,571,056 ft) which is the wavelength of a 1 hertz radio signal . A 1 megahertz radio signal has a wavelength of 299.8 meters (984 ft). </P>

Do radio waves penetrate the earth's atmosphere