Radio waves make up the part of the electromagnetic spectrum with the longest wavelengths. Radio waves are used in radio and television broadcasts, satellite transmissions and cell phone signals. Astronomical objects give off radio waves which can be detected by radio telescopes.
Radio waves can be used to carry information through amplitude modulation or frequency modulation, which are abbreviated to A.M. and F.M. Amplitude is the height of the wave, and frequency is the number of vibrations of the wave in one second. In amplitude modulation, the information that the wave carries is encoded in variations of the amplitude, whereas in frequency modulation, the frequency varies.
Planets, comets and other astronomical objects also emit radio waves as a result of nuclear reactions. These radio waves are emitted at extremely long wavelengths and can be detected by radio telescopes. A large collection of radio telescopes is found at the Very Large Array in New Mexico, where a series of telescopes work together to interpret radio waves into images. This arrangement is known as an interferometer, because it images the sky by collecting data on the interference patterns of radio waves from astronomical objects.
Man-made radio waves are created by running an electrical current through a wire, which generates an electromagnetic field. As the field builds up, the wave disperses outwards from the wire. If current is applied repeatedly, a wave pattern forms. This basic mechanism underlies all radio transmitter technology.