Microwave is a short wavelength radio wave. It varies from 1 to 300 millimeters (about 1/25 to 12 inches) in length. Like light waves, microwaves may be reflected and concentrated. They pass easily through rain, smoke, and fog, which block visible light waves. They can also pass through the ionosphere, which surrounds Earth and blocks or reflects longer radio waves. Thus, microwaves are well suited for long-distance, satellite, and space communications and for navigation signals.
Microwaves first came to public notice through the use of radar in World War II (1939-1945). Today, many satellite communications systems and radio telescopes use them. In TV, microwave transmission sends programs from pickup cameras in the field to the TV transmitter. These programs can then be sent via satellites to locations around the world. Microwaves can also cook food in microwave ovens.
