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.
(born Oct. 22, 1905, Norman, Okla., U.S.—died Feb. 14, 1950, Red Bank, N.J.) U.S. engineer. He graduated from the University of Wisconsin and went to work for Bell Telephone Laboratories. Assigned to track down sources of static that could interfere with radiotelephone communication, he discovered (1931) the first extraterrestrial source of radio waves, emanating from the constellation Sagittarius in the direction of the Milky Way Galaxy's centre. The discovery proved that celestial bodies could emit radio waves and marked the beginning of radio astronomy.
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