An acronym for "radio detection and ranging," radar starts with the transmission of a radio beam. When outgoing waves strike an object such as a plane, a portion of their energy reflects back to the sending station. Because the waves travel at a known speed, it's possible to calculate the object's exact distance, while other measures pinpoint direction, elevation, and speed. Developed independently in the U.S., Britain, and elsewhere in the 1930s, radar played a pivotal role in air defense and naval battles during World War II. In peacetime, the technology has had wide application in weather tracking, air-traffic control, and astronomy.

Related Links
Book Excerpt: "The Invention That Changed the World" by Robert Buderi