Electromagnetic radiation is defined as "the emission and transmission of energy in the form of electromagnetic waves” (Chang, pp. 246). An electromagnetic wave consists of two waves at perpendicular planes, on representing the electrical field while the other represents the magnetic field. This spectrum is split up into about 81 octaves, much like the octaves of sound, which scientists have categorized in order to depict the usefulness of the different properties. Theoretically electromagnetic waves can be as long as the expansive width of the universe in one wave, to a wavelength the size of a quanta (the smallest amount of energy that can be transmitted). That, however, is at this point in time negligible because we either cannot detect wavelengths so extremely large or infinitesimally small. So generally the spectrum is regarded to be set between 30,000,000 km and .0001 angstroms (1 km is equal to 1 X 10^13 angstroms).
The longest and least energetic of the accepted wavelengths are radio waves. Their wavelengths range from 300,000 km to 30 cm and a frequency of 30 kHz to 3,000,000 kHz. The waves are used in the transmission of radio and television signals. AM and FM radio signals fall in the long-wave radio range, while TV signals use the short-wave radio range, somewhere in the 3 m wavelength. Radio waves take up about 30 of the 81 octaves.
The next slightly more energetic and shorter wavelength is microwaves. Obviously, most are familiar with microwaves since they are always being used to cook food, but microwaves are also used in radiotelescopes and radar, even the radiation from a neutral hydrogen atom falls in this range. Microwave range extends from wavelengths of 30 cm to .3 cm and frequencies of 1-100 billion cycles per second. This corresponds to 6 1/2 octaves.
Then comes the infrared range. While much of the radio spectrum passes easily through our atmosphere, infrared is almost completely blocked off due to absorption by gaseous molecules that reside there.