Jansky, Karl Guthe (1905-1950)

US radio engineer who in 1932 discovered that the Milky Way galaxy emanates radio waves; he did not follow up his discovery, but it marked the birth of radioastronomy.

Jansky was born in Norman, Oklahoma, and graduated in physics from the University of Wisconsin. In 1928 he joined the Bell Telephone Laboratories, New Jersey, where he investigated causes of static that created interference on radio-telephone calls.

Jansky noticed that the background hiss on a loudspeaker attached to his specially built receiver and antenna system reached a maximum intensity every 24 hours. It seemed to move steadily with the Sun but gained on the Sun by four minutes per day. This amount of time correlates with the difference of apparent motion, as seen on Earth, between the Sun and the stars, so Jansky surmised that the source must lie beyond the Solar System. By 1932, he had concluded that the source lay in the direction of Sagittarius - the centre of our Galaxy.