Archive for April, 2005

Karl G. Jansky

Sixty years ago this month, the PROCEEDINGS OF THE INSTITUTE OF RADIO ENGINEERS (IRE) included Karl Jansky’s classic paper reporting reception of “electromagnetic waves of an unknown origin” but believed to be from “some source outside the solar system.” Jansky, a research engineer with the Bell Telephone Laboratories, stated that he initially had detected the mysterious waves in 1931 and had continued with a “comprehensive study of them ” during 1932. He had used a slowly rotating directional antenna, a receiver tuned to 14.6 m, and a chart recorder to obtain data on the direction and intensity of the waves as a function of time. Analysis of the data led Jansky to conclude that “the waves come, not from the sun, but from a direction which remains constant throughout the year.” He noted that the waves seemed to come approximately from the direction of Sagittarius in the Milky Way although his system was not accurate enough to identify a specific source.

Jansky was born in 1905 in Norman, OK, where his father was Dean of Engineering at the University. Jansky was named for Karl Guthe, a German-American physicist and teacher whom his father admired. In 1908 the Jansky family moved to Madison, WI, where his father became a professor and where Karl developed an early, interest in radio. He graduated in physics from the University of Wisconsin in 1927 and played on the ice hockey team while in school. He taught for a year at Wisconsin and later received the M.S. degree in 1936. He accepted a job offer at the Bell Telephone Laboratories in July 1928 and spent about two years at a radio laboratory in Cliffwood, NJ .

Jansky’s first assignment was to investigate natural sources of radio static, and he undertook construction of a short-wave recording system in addition to doing measurements of static interference with long-wave reception. His project suffered a temporary interruption when the laboratory was moved to a new site in Holmdel, NJ, a few miles away. By December 1931, he had managed to identify three sources of short-wave static: local thunderstorms, distant storms, and a steady hiss of uncertain origin. Initially he suspected that the third form of noise came from the sun but, as his observations were continued over the next several months, he realized that the origin was from beyond the solar system. In a later PROCEEDINGS paper published in October 1935, he wrote that the “interstellar interference” might be due to thermal agitation of electrically charged particles.

Many years later, it was determined by others that the noise observed by Jansky was synchrotron emission from electrons in regions with intense magnetic fields near the center of the galaxy. His failure to detect radio noise emission from the sun has been attributed to the fact that his observations were made during a near minimum of the eleven-year sunspot cycle. Radio frequency emission from the sun was in fact detected by J. S. Hey in Great Britain in February 1942 and by Grote Reber in the United States in 1943. It has been speculated that astronomers might have taken an earlier interest in Jansky’s work if he had identified the sun as a radio source. Although the significance of his findings was not fully appreciated .at the time they were reported in the early 1930’s, his identification of extraterrestrial radio noise did mark the effective beginning .of the new science of radio astronomy.

During World War II, Jansky engaged in research on radio direction finders and later worked on development of more sensitive amplifiers. Declining health after the war caused him to require protracted leaves of absence from work and led to an untimely death in February 1950 at age 44. There was a growing interest in the field of radio astronomy in the postwar years. When a national radio astronomy observatory was established in 1958 in Green Bank, WV, the main building was named for Jansky in honor of his pioneering contribution.

James E. Brittain
School of History, Technology, and Society
Georgia Institute of Technology

Submitted by Dick Reiman, Historian

Copyright 1993 IEEE. Reprinted with permission from the IEEE publication, “Scanning the Past” which covers a reprint of an article appearing in the Proceedings of the IEEE Vol. 81, No.10, October 1993.

April 4th, 2005


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