Jansky's Early Radio Astronomy
At Bell Labs Karl Jansky Discovered Celestial Short-Wave Signals
May 20, 2008
Karl Jansky
Karl Jansky was born in Oklahoma in 1905 but moved to Wisconsin three years later. After being raised in Wisconsin and graduating with a degree in physics from the University of Wisconsin, Jansky started working for Bell labs (forerunner to AT&T) in 1928. Because he had chronic kidney disease Bell labs almost didn't hire Jansky. However an older brother who had previously worked at Bell labs intervened for him.
Jansky's Work at Bell Labs
Bell labs was primarily interested in telephone communications. In Jansky's time short-wave radio transmissions were used for long distance and transatlantic telephone communications. Consequently the noise or static in these radio frequencies reduced the quality of these early telephone communications.
Therefore Jansky's job assignment at Bell labs was to study this short-wave (20.5 MHz) radio static and if possible design receivers to minimize the noise. This was a purely applied problem, but Jansky made a fundamental discovery, celestial radio waves, that revolutionized astronomy.
For the first two years, Jansky worked at the Cliffwood, New Jersey laboratory, but he moved to the Holmdel, New Jersey laboratory in 1930.
First Jansky needed a short-wave radio antenna and receiver. This equipment is relatively common today, but in Jansky's time radio was relatively new and the techniques for building radio receivers were less established. Hence it took Jansky a couple years to build and modify the equipment for his work.
To study the direction of the radio waves, Jansky's antenna was mounted on wheels from a model T car and rotated like a merry-go-round.
Jansky started detailed studies of the radio static in late 1930. He identified three sources of static. The first two were thunderstorms, both distant and local. The third source of radio noise was more difficult to identify. Jansky noticed that the strength of this static varied with a time period equal to the time Earth rotates on its axis. That told him the radio waves originated outside the solar system. These radio waves originated from the direction of the constellation Sagittarius and turned out to be from the core of the Milky Way Galaxy. Jansky had discovered the first celestial radio signals. Jansky published a series of papers on these celestial radio waves during the 1930s. His discovery was also featured in the May 5, 1933 issue of the New York Times.
The Origin of Radio Astronomy
Jansky's discovery of celestial radio signals was the origin of radio astronomy, so Jansky is considered the father of radio astronomy. In his honor astronomers measure the strength of celestial radio signals in units of janskys.
However the astronomical community greeted Jansky's discovery by resoundingly ignoring it. Bell labs declined Jansky's request to build a larger receiver. With the advent of World War II, Jansky, like most American scientists and engineers, was assigned to defense related projects. After the war ended, Jansky's kidney disease worsened. He died at age 44 on February 14, 1950.
Most astronomers ignored Jansky's discovery, but Grote Reber and John Kraus, inspired by Jansky's work, built radio receivers and began doing radio astronomy. Building on the work of these pioneers, radio astronomy is now a very important branch of astronomy.
Further Reading
Friis, H.T., "Karl Jansky: His Career at Bell Telephone Laboratories", Science, Vol. 149, p. 841-842, August, 1965.
Sullivan, W.T., Classics in Radio Astronomy, Springer Verlag, 1982.
Zeilik, M. Astronomy: The Evolving Universe, 9th ed. Cambridge, 2002.
 |
 |
