The development of radio astronomy. In 1931, Karl Jansky, an American engineer at the Bell Telephone Laboratories in New Jersey, studied static that was interfering with short-wave communication systems. He found that the static appeared four minutes earlier each day. Jansky knew that the stars rise four minutes earlier daily, and so he concluded that the static must be coming from beyond the solar system. He was actually receiving radio waves from the center of our galaxy.
Professional astronomers did not follow up on Jansky's discovery. However, an American amateur astronomer named Grote Reber designed a radio telescope and operated it in his backyard beginning in the late 1930's. Radio astronomy finally began to flourish after World War II (1939-1945). The study of radio waves from space greatly expanded astronomers' knowledge of the structure, size, and history of the universe. For example, it revealed a great deal of new information about the clouds of gas and dust between the stars in our galaxy. During the 1960's, radio astronomers played an important role in the discovery of quasars and pulsars. In 1965, astronomers testing a radio telescope and receiver system discovered the primordial background radiation, which astronomers believe was produced when the universe began with the big bang.
Excerpt from the "Astronomy" article, The World Book Encyclopedia © 1999