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date: 21 February 2020

Jansky, Karl Guthefree

(22 October 1905–14 February 1950)
  • Thomas R. Williams

Jansky, Karl Guthe (22 October 1905–14 February 1950), electrical engineer and discoverer of radio emissions originating in the Milky Way galaxy, was born in Norman, Oklahoma, the son of Cyril Methodius Jansky and Nellie Moreau. His father, after 1908 a professor of electrical engineering at the University of Wisconsin, stimulated his intellectual growth through chess and bridge and family discussions that resembled critical debates. Jansky’s lifelong interest in electronics began when as a child he built a crystal radio and continued into his senior thesis on vacuum tubes at the University of Wisconsin. He was elected to Phi Beta Kappa and received a B.S. in physics in 1927. He was awarded an M.S. in physics by the same institution in 1936.

After a year as a graduate student, and instructor, Jansky sought employment at the Bell Telephone Laboratories. A pre-employment physical examination revealed that his kidneys had been damaged by Bright’s disease. Intercession by his brother C. Moreau Jansky, a former Bell Labs employee who knew the corporate doctors, overcame their objections, and Jansky joined Bell Labs in August 1928. He married Alice La Rue Knapp in 1929; they had two children.

Assigned to the reception branch of the Bell Labs Radio Research Division at Cliffwood, New Jersey, Jansky worked in a small research group supervised by Harald Friis. His first project was to identify the sources of static that regularly interfered with transoceanic radiotelephone communications and specifically to determine the angle and direction from which the radio noise arrived at an antenna. To attack this problem Jansky designed a large antenna that rotated around its short central axis in the horizontal plane once every twenty minutes. The project was delayed by relocation of the laboratory to Holmdel, but by August 1931 Jansky recognized that his 24-hour recordings exhibited a regular maximum of steady, hiss static in addition to episodic peaks correlated with local or distant storms. Initially Jansky associated the daily maximum with the sun, but it soon became apparent that the noise maximum was moving away from the sun. Within six months he was certain that the hiss static maximum was extraterrestrial in origin. In April 1932 Friis agreed and directed Jansky to prepare a report of his results. Published later that same year in Proceedings of the Institute of Radio Engineers (PIRE), the paper carried an ultraconservative title that, following Friis’s directions, obscured the revolutionary nature of Jansky’s findings: “Directional Studies of Atmospherics at High Frequencies.”

As laboratory staffing shrank because of the depression, Jansky was assigned other research projects. By December 1932, however, with a few additional observations and tutoring from his Bell Labs colleague A. M. Skellett, Jansky became certain that the steady hisslike static originated at a fixed point in space that apparently moved across the sky each day because of the earth’s rotation. With some difficulty he developed approximate celestial coordinates for that point. Then, in two PIRE papers published in 1933, he described the basic astronomy involved; in language again conservatively guided by Friis, he articulated his revolutionary claim that the hiss static seemed to have its origin in our Milky Way galaxy, with a maximum in a direction that pointed close to the galactic center. Other work priorities soon displaced research on this galactic radio noise, and after 1936 Jansky made no more observations.

Astronomers were not completely unresponsive to Jansky’s discovery, although his only direct effort to stimulate their interest was with one 1933 paper in Popular Astronomy. The following year Harlan True Stetson discussed Jansky’s discovery in his book on radio waves and their interaction with the earth. Fred Whipple, his student Jessie Greenstein at Harvard University, and others hypothesized that the radio energy detected by Jansky originated in interstellar dust. Greenstein in particular seems to have been convinced of the importance of Jansky’s observations. Still, Friis was correct in noting in his retrospective assessment that there had been no encouragement to Jansky from the astronomical community, despite nationwide publicity surrounding his initial discovery.

After 1936 Jansky’s work continued to involve improvements in radiotelephony, including projects on siting receivers for transatlantic radio communications and on manmade sources of radio noise. He received a citation for his research on radio direction finding during World War II. Jansky’s health was never secure and declined rapidly after 1945. Progressive failure of his kidneys led to hypertensive cardiovascular disease, the underlying cause of his death from a cerebral thrombosis in Red Bank, New Jersey.

Jansky’s observation of extraterrestrial radio waves and his identification of their origin in the direction of the galactic center were among the most important fundamental astronomical discoveries of the twentieth century. As a result of his observations and those of later experimenters, astronomers broadened their focus from visible light, for millennia the sole medium of astronomical observation, to include radiation at both higher and lower frequencies, a shift that transformed astronomy and greatly enlarged the understanding of the universe. Although Jansky was unable to pursue this interest and was never honored for his discovery during his lifetime, his work was taken up by others. In 1944 Grote Reber published the first crude radio map of the sky, based on observations with a homemade parabolic reflector in Wheaton, Illinois. After World War II British and Australian engineers, working with surplus radio and radar equipment, refined Reber’s map and identified discrete radio sources, many of which were soon correlated with optical counterparts. Thereafter radio astronomy grew in importance during the last half of the twentieth century. In recognition of his contribution the basic unit of measurement for flux density (for any wavelength of radiation) is named the jansky.


Jansky’s working notebooks and papers are in the Bell Telephone Laboratories Archives. Some of his letters to family members are in the C. M. Jansky Papers in the University of Wisconsin Archives. Jansky’s articles in the Proceedings of the Institute of Radio Engineers in 1932 (pp. 1920–32), 1933 (pp. 1158–63, 1517–30), and 1935 (pp. 1517–30), are well illustrated. See also his articles in Nature 132 (8 July 1933): 66, and Popular Astronomy 44, no. 10 (Dec. 1933): 548–55. C. Moreau Jansky reminisced about his brother in a talk published in American Scientist 45 (Jan. 1957): 5–12. A biographical essay is W. T. Sullivan III, “Karl Jansky and the Discovery of Extraterrestrial Radio Waves,” in his The Early Years of Radio Astronomy (1984). Sullivan reviews a controversy that arose after Jansky’s death, centering on Friis’s conservative approach to the announcement of Jansky’s discovery, as well as allegations that Jansky’s desire to continue working on his discovery was thwarted by Friis. The debate was prompted by Jansky’s later supervisor, George C. Southworth, in “Early History of Radio Astronomy,” Scientific Monthly 82 (Feb. 1956): 55–66, and it was possibly encouraged by C. Moreau Jansky, “The Discovery and Identification by Karl Guthe Jansky of Electromagnetic Radiation of Extraterrestrial Origin in the Radio Spectrum,” Proceeding of the Institute of Radio Engineers 46 (1958): 13–15. Friis published an account in his own defense, “Karl Jansky: His Career at Bell Telephone Laboratories,” Science 149 (1965): 841–42.