Radio waves are a part of the electromagnetic spectrum. Just as an optical telescope gathers visible light and magnifies it, a radio telescope is a large dish-shaped device that gathers and amplifies radio frequencies from space. Radio telescopes do not "see" the way an optical telescope does; the radio signals the telescopes gather are used to create diagrams showing where the strongest radio sources are located.

Cosmic radio waves were discovered accidentally by Karl Jansky (1905-1950) in 1932. He had been using a receiver to search for the source of radio noise that was interfering with long distance radio-telephone conversations. That the source could be out in the cosmos was a big surprise, but there was no follow-up to the discovery because radio astronomy did not exist as a science.

One person, an amateur ham-radio enthusiast named Grote Reber, was electrified by Jansky's discovery. Reber built the...