Karl Guthe Jansky

Karl Guthe Jansky
Born	(1905-10-22)October 22, 1905 Norman, Oklahoma, U.S.
Died	February 14, 1950(1950-02-14) (aged 44) Red Bank, New Jersey, U.S.
Nationality	American
Known for	Radio astronomy
Scientific career
Fields	Physics Radio astronomy

Karl Guthe Jansky (October 22, 1905 – February 14, 1950) was an American physicist and radio engineer who in August 1931 first discovered radio waves emanating from the Milky Way. He is considered one of the founding figures of radio astronomy.

Early life

Karl Guthe Jansky was born in what was then the Territory of Oklahoma where his father, Cyril M. Jansky, was Dean of the College of Engineering at the University of Oklahoma at Norman. Cyril M. Jansky, born in Wisconsin of Czech immigrants, had started teaching at the age of sixteen. He was a teacher throughout his active life, retiring as Professor of Electrical Engineering at the University of Wisconsin. He was an engineer with a strong interest in physics, a trait passed on to his sons. Karl Jansky was named after Dr. Karl Eugen Guthe, a Professor of Physics at the University of Michigan who had been an important mentor to Cyril M. Jansky.

Karl Jansky's mother, born Nellie Moreau, was of French and English descent. Karl's brother Cyril Jansky Jr., who was ten years older, helped build some of the earliest radio transmitters in the country, including 9XM in Wisconsin (now WHA of Wisconsin Public Radio) and 9XI in Minnesota (now KUOM).

Karl Jansky attended college at the University of Wisconsin where he received his BS in physics in 1927. In 1928 he joined the Bell Telephone Laboratories site in Holmdel, New Jersey. Bell Labs wanted to investigate atmospheric and ionospheric properties using "short waves" (wavelengths of about 10–20 meters) for use in transatlantic radio telephone service. As a radio engineer, Jansky was assigned the job of investigating sources of static that might interfere with radio voice transmissions.

Radio astronomy

At Bell Telephone Laboratories Jansky built an antenna designed to receive radio waves at a frequency of 20.5 MHz (wavelength about 14.6 meters). It was mounted on a turntable that allowed it to be rotated in any direction, earning it the name "Jansky's merry-go-round". It had a diameter of approximately 100 ft. and stood 20 ft. tall. By rotating the antenna on a set of four Ford Model-T tires, the direction of a received signal could be pinpointed. A small shed to the side of the antenna housed an analog pen-and-paper recording system.

After recording signals from all directions for several months, Jansky eventually categorized them into three types of static: nearby thunderstorms, distant thunderstorms, and a faint steady hiss of unknown origin. He spent over a year investigating the source of the third type of static. The location of maximum intensity rose and fell once a day, leading Jansky to initially surmise that he was detecting radiation from the Sun.

After a few months of following the signal, however, the brightest point moved away from the position of the Sun. Jansky also determined that the signal repeated on a cycle of 23 hours and 56 minutes, the period of the Earth's rotation relative to the stars (sidereal day), instead of relative to the sun (solar day). By comparing his observations with optical astronomical maps, Jansky concluded that the radiation was coming from the Milky Way and was strongest in the direction of the center of the galaxy, in the constellation of Sagittarius.

His discovery was widely publicized, appearing in the New York Times of May 5, 1933. He published his classic paper "Electrical disturbances apparently of extraterrestrial origin" in Proc. IRE in 1933. This paper was re-printed in Proc. IEEE in 1984 (for their centennial issue, where they note the research most likely would have won a Nobel prize, had not the author died young) and again in 1998, for the first centennial of radio. Jansky wanted to follow up on this discovery and investigate the radio waves from the Milky Way in further detail. He submitted a proposal to Bell Labs to build a 30 meter diameter dish antenna with greater sensitivity that would allow more careful measurements of the structure and strength of the radio emission. Bell Labs, however, rejected his request for funding on the grounds that the detected emission would not significantly affect their planned transatlantic communications system. Jansky was re-assigned to another project and did no further work in the field of astronomy.

Follow-up

Several scientists were interested in Jansky's discovery, but radio astronomy remained a dormant field for several years, due in part to Jansky's lack of formal training as an astronomer. His discovery had come in the midst of the Great Depression, and observatories were wary of taking on any new and potentially risky projects.

Two men who learned of Jansky's 1933 discovery were of great influence on the later development of the new study of radio astronomy: one was Grote Reber, a radio engineer who singlehandedly built a radio telescope in his Illinois back yard in 1937 and did the first systematic survey of astronomical radio waves. The second was Prof. John D. Kraus, who, after World War II, started a radio observatory at Ohio State University and wrote a textbook on radio astronomy, long considered a standard by radio astronomers.

Legacy and death

Full-size replica of Jansky's radio telescope, now at the National Radio Astronomy Observatory

In honor of Jansky, the unit used by radio astronomers for the strength (or flux density) of radio sources is the jansky (1 Jy = 10⁻²⁶ W m⁻² Hz⁻¹). The crater Jansky on the Moon is also named after him. The NRAO postdoctoral fellowship program is named after Karl Jansky. Additionally, NRAO awards the Jansky Prize annually in Jansky's honor. On January 10, 2012, the NRAO announced the Very Large Array (VLA), the radio telescope in Magdalena, New Mexico, would be renamed the Karl G. Jansky Very Large Array in honor of Karl Janksy's contribution to Radio Astronomy.

A full-scale replica of Jansky's original rotating telescope is located on the grounds of the NRAO site (38°25′53.9″N 79°48′58.5″W) in Green Bank, West Virginia, near a reconstructed version of Grote Reber's 9-meter dish.

The original site of Jansky's antenna (40°21′54.5″N 74°09′48.9″W) at what is now the vacant Bell Labs Holmdel Complex at 101 Crawfords Corner Road, Holmdel, New Jersey, was determined by Tony Tyson and Robert Wilson of Lucent Technologies (the successor of Bell Telephone Laboratories) in 1998, and a monument and plaque were placed there to honor the achievement. The monument is a stylized sculpture of the antenna and is oriented as Jansky's antenna was at 7:10 p.m. on September 16, 1932, at a moment of maximum signal caused by alignment with the center of our galaxy in the direction of the constellation Sagittarius.

Jansky noise is named after Jansky, and refers to high frequency static disturbances of cosmic origin.

Jansky was a resident of Little Silver, New Jersey, and died at age 44 in a Red Bank, New Jersey, hospital (now called Riverview Medical Center) due to a heart condition.

Selected writings

• 1932: Directional studies of atmospherics at high frequencies, Proc. IRE, 20, p. 1920.
• 1933: Electrical disturbances apparently of extraterrestrial origin, Proc. IRE, 21, p. 1387. (Reprinted  in Proc. IEEE, vol. 86, no. 7 (July 1998), pp. 1510–1515.) Published with the reprint is an explanatory article Introduction To "Electrical Disturbances Apparently Of Extraterrestrial Origin" .
• 1933: "Radio waves from outside the solar system", Nature, 132, p. 66.
• 1933: "Electrical phenomena that apparently are of interstellar origin", Popular Astronomy, 41, p. 548, Dec., 1933.
• 1935: A note on the source of interstellar interference, Proc. IRE, 23, p. 1158.
• 1937: Minimum noise levels obtained on short-wave radio receiving systems, Proc. IRE, 25, p. 1517.

See also

• Reber Radio Telescope
• Astronomical radio source

References

• Sullivan, W. T., ed. (2005), The Early Years of Radio Astronomy: Reflections Fifty Years After Jansky's Discovery, Cambridge University Press, ISBN 0-521-61602-6. In particular Chap.1 by Sullivan, "Karl Jansky and the discovery of extraterrestrial radio waves," pp. 3–42.

External links

• My Brother Karl Jansky and His Discovery of Radio Waves from Beyond the Earth
• F. Ghigo (2006-02-07). "Karl Jansky and the Discovery of Cosmic Radio Waves". National Radio Astronomy Observatory. Retrieved 2006-08-24.
• Serendipitous Discoveries in Radio Astronomy: Honoring the 50th Anniversary Announcing the Discovery of Cosmic Radio Waves by Karl G. Jansky on May 5, 1933
• Accompanying 3 photos: from 1962, from c.1960 (with Grote Reber), and one of Karl Jansky, another astronomy pioneer, from c.1930.
• Encyclopedia of Oklahoma History and Culture - Jansky, Karl
• http://www.nrao.edu/whatisra/hist_jansky.shtml
• http://www.bell-labs.com/news/1998/june/4/2.html