What is Radio wave?
[[File:Dipole xmting antenna animation 4 408x318x150ms.gif|thumb|Diagram of an antenna emitting radio waves]] '''Radio waves''' make up part of the [[electromagnetic spectrum]]. These [[wave (physics)|wave]]s are packets of energy with differing [[wavelength]]s, similar to [[visible light]] waves, [[X-ray]]s or [[gamma ray]]s, except much longer. A radio wave, like other [[electromagnetic wave]]s, is similar to an [[ocean surface wave]] or any other type of wave. Both types of wave have a hill and valley shape, repeating over and over. A [[wavelength]] is measured as the distance from the top of one crest to the top of its neighboring crest. While the wavelength of visible light is very very small, less than one micrometer and much less than the thickness of a human hair, radio waves can have a wavelength from a couple [[centimeter]]s to several [[metre|meter]]s. They also have a [[radio frequency]]. The smallest radio waves are called [[microwave]]s. [[Shortwave]]s are not quite so small. There are also medium and long waves. [[Antenna]]s designed to send and receive radio waves are usually similar in size to the wavelength they are to use. Many radio antennas (like those on cars) are made long because they receive signals of [[FM radio]] (a few meters, several feet) or [[AM radio]] (hundreds of meters, about a thousand feet). == Uses == [[Manmade]] radio waves have been used since the 19th century for [[communication]]. [[Radar]] was developed in the 20th century, using radio waves to 'see' distant objects by [[Reflection|bouncing]] waves off an object and seeing how long it takes for the waves to return. [[Radio]]s also use these waves to send and receive information. Radio waves from other planets were first discovered in the 1930s by [[Karl Guthe Jansky]], working for [[Bell Laboratories]]. Bell was detecting [[noise (electronics)]] on radio channels, and had Jansky try to find the source of this static, or [[interference]]. After identifying noise that came from [[lightning]], he spent much time