Radio engineer, born in Norman, Oklahoma, USA. He studied at the University of Wisconsin and joined Bell Telephone Laboratories in 1928. His fundamental discovery (1932) was of radio waves from outer space, while working on interference suffered by radio reception. This discovery allowed the development of radio astronomy during the 1950s. The unit of radio emission strength, the jansky, is named after him.
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
Jansky was born in Norman, Oklahoma, to a Czech-American family. 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).
Education and engineering
Jansky attended college at the University of Wisconsin where he received his BS in physics in 1927. 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
Jansky built an antenna designed to receive radio waves at a frequency of 20.5 MHz (wavelength about 14.6 meters).
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. 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 the galaxy, in the constellation of Sagittarius. 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.
Follow-up
Several scientists were interested by 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.
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. John Kraus, who, after World War II, started a radio observatory at Ohio State University and wrote a textbook on radio astronomy, still considered a standard by many radio astronomers.
Legacy
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 Hz-1).
A full-scale replica of Jansky's original rotating telescope is located on the grounds of the NRAO site in Green Bank, West Virginia, near a reconstructed version of Grote Reber's 30m dish.
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