Jansky, Karl Guthe, 1905–50, American radio engineer; b. Norman, Okla. After graduating (1927) from the Univ. of Wisconson, he joined the Bell Telephone Laboratories. While trying to determine the causes of radio communications static, Jansky discovered (1931) radio waves from extraterrestrial sources—a discovery that prompted the investigations of Gröte Reber and led to the development of the science of radio astronomy. By 1932 Jansky had concluded that the source of the interference was located in the direction of the center of the Milky Way galaxy.
Jansky's discovery was serendipitous. Not only was it by chance that he had chosen a frequency at which the galactic center emits large amounts of radiation and at which the earth's atmosphere is transparent, he also was working at a period of minimum sunspot activity which occurs only every 11 years. At sunspot maximum, the ionosphere would have blocked all extraterrestrial radio waves at the 20 MHz frequency, and signals from the Milky Way would not have been detected.