Jansky, Karl (1905-1950)

views updated May 17 2018

Jansky, Karl (1905-1950)

American radio engineer

One of the ways modern astronomers study the Universe is by tracing light waves through telescopes; another is by studying radio waves. The man who discovered the existence of these extraterrestrial radio waves, and thus founded radio astronomy , was Karl Jansky. Employed as an engineer in Bell Laboratories, New Jersey, Jansky was assigned the job of reducing static noise on transatlantic radio transmissions, and it was while inquiring into the origin of this static that he made his discovery.

The third of six children, Karl Guthe Jansky was born in Norman, Oklahoma, while that region was still a territory. His father, Cyril Jansky, was a college professor who taught electrical engineering and eventually became the head of the School of Applied Science at the University of Wisconsin. Jansky was named after Karl Guthe, a German-born physicist under whom his father had studied at the University of Michigan. Jansky attended the University of Wisconsin, where he played on the ice hockey team. He hoped to join the Reserve Officer's Training Program there but was diagnosed with a chronic kidney condition called Bright's disease; Jansky suffered from it all his life. He wrote his senior thesis on vacuum tubes and earned his B.S. in physics in June 1927. He stayed on at the University of Wisconsin for another year and supported himself by teaching while studying to complete the course work for his master's degree. He did not, however, write a thesis, and it would be years before he actually earned the degree.

After leaving the University of Wisconsin, Jansky applied for work at the Bell Communications Laboratories. The company was reluctant to hire him because of possible complications from Bright's disease. But Jansky's older brother, a professor of electrical engineering at the University of Minnesota, knew many Bell personnel. He intervened on behalf of his younger brother and secured the job for Jansky. Fearful of the stress he might suffer if he worked at their headquarters in New York City, the company assigned Jansky to work at its facilities in New Jersey.

Although transatlantic radio communication was possible in the early 1930s, it was very expensive and poor in quality. It cost 75 dollars to talk for three minutes from New York to London, and the transmissions, which occurred not through cables but through radio waves, were routinely interrupted by static. There were clicking, banging, crackling, and hissing noises that sometimes obliterated the conversation. At Bell, Harald Friis assigned Jansky the job of determining what was causing the static. This was in the summer of 1931, and the first step Jansky took to resolve the problem was to design a new antenna. He built a directional antenna that was capable of receiving a much wider range of wavelengths than conventional antennas of the time. He also developed a receiver that generated as little static as possible, to minimize its interference with his efforts to measure static from outside sources. Last, Jansky developed an averaging device for recording the variations in static. The antenna and the rest of the equipment were installed in Holmdel, New Jersey, a rural area where there would be very little interference from man-made radio signals.

The antenna that Jansky assembled at Holmdel was mounted on wheels and moved on a turntable. This allowed it to scan the sky in all directions once every 20 minutes; it could also be pointed at different heights above the horizon. Known as Jansky's "merry-go-round," the antenna is believed to have been the largest of its type at the time. It operated at 20 MHz or 14.6 meters. He categorized the static into three different types: local thunderstorms, distant thunderstorms, and steady static. Jansky was able to establish that thunderstorms were the source of clicks and bangs. But he observed of the last type of static, as quoted in Mission Communications: The Story of Bell Laboratories, that it was "a very steady hiss type static, the origin of which is not yet known."

Jansky recorded the intensity of the hiss-type static, and he observed that it peaked when the antenna was pointed at a certain part of the sky. At first, Jansky thought that the point of peak intensity followed the Sun , and he initially assumed that the static was solar-generated. However, as he continued to make his observations, he saw that the peaks were moving further and further from the Sun. Indeed, he observed that the peak intensities occurred every 23 hours and 56 minutes. This was perhaps the first time that Jansky truly considered the idea that this static could have an extraterrestrial origin.

Jansky knew little about astronomy, but after consulting some colleagues who did, he learned that while Earth takes 24 hours to rotate once on its axis in relation to the Sun, its rotation with respect to the stars is four minutes shorter. Known as a sidereal day, this phenomenon was precisely what Jansky had observed: peak intensities in static readings that occurred at intervals of 23 hours and 56 minutes. Although the existence of radio waves other than those generated by people on Earth had never even been considered as a possibility, Jansky did not doubt his findings. He had made a discovery that was entirely new, and he had done it by accident. He was also fortunate in another respect. His investigations were conducted at a time when the 11-year cycle of solar activity was at a minimum, which rendered the ionosphere transparent to 20 MHz wavelengths at night. If this had not been the case, solar flares would have drowned out the weak hisses from space , and Jansky would never have been able to measure them.

Jansky had observed that the static was most intense when his antenna was aimed at the center of the Milky Way, the galaxy in which Earth is located. His measurements indicated a direction of 18 hours right ascension and 10 degrees declination. Such a location put the peak static emissions in the constellation of Sagittarius. These observations led Jansky to form two hypotheses concerning the origin of the static; either radio sources are distributed much as the stars are in the galaxy, or the radio emissions come from stars like our own sun. Since Jansky never did pick up such emissions from the Sun (weaker types were found by others), he rejected the second theory; his investigations during a partial solar eclipse in 1932 also seemed to support his belief that the Sun was not emitting radio waves. The first hypothesis was supported by the fact that radio emissions were most intense from the center of the Milky Way, which contains the densest clusters of stars. Jansky also reasoned that the emissions from space would be found all along the electromagnetic spectrum , a hypothesis confirmed by later researchers.

It was in December 1932 that Jansky realized the extraterrestrial nature of the static he was studying, and he issued his first report on the subject that same month in a paper entitled "Directional Studies of Atmospherics at High Frequencies." He presented it to the Institute of Radio Engineers, but no one made much of his discovery. Indeed, Jansky's boss, Harald Friis, cautioned him against proposing that static came from extraterrestrial sources in case he should be proved wrong. In April 1933, Jansky presented a second paper on these radio signals at a meeting of the International Scientific Radio Union in Washington, D.C. On May 5, 1933, Bell Laboratories issued a press release on the subject, and the next day the New York Times headlined his work as "New Radio Waves Traced to the Center of the Milky Way." On May 15, NBC's Blue Network broadcast a sample of Jansky's "star noise" to the nation. It was described by reporters as "sounding like steam escaping from a radiator." Jansky presented his second paper again at the annual convention of the Institute of Radio Engineers (IRE) in June 1933, and it was published the following October.

While researching "star noise," Jansky worked on other projects. He designed a new receiver that could automatically change bandwidths, as well as studied the general effects of bandwidth on an incoming signal. When Bell realized that nothing could be done about the hiss-type static that Jansky was studying, they assigned him to a different project. Jansky wrote to his father in January 1934, as quoted in the Invisible Universe Revealed : "I'm not working on the interstellar waves anymore. Friis has seen fit to make me work on the problems of and methods of measuring noise in general. A fundamental and necessary work, but not near as interesting as interstellar waves, nor will it bring near as much publicity. I'm going to do a little theoretical research of my own at home on the interstellar waves, however." Although Jansky presented his findings to astronomers, they largely ignored the implications of his work. One reason was that they did not believe the Milky Way could possibly be such a giant and intensive radio source. Resources were also scarce during the Great Depression of the 1930s, and there was little money for equipment to pursue this discovery. But the primary reason Jansky's work was neglected was that astronomy was then an optical venture. No one had any idea what to do with radio measurements. Jansky was, however, able to use his papers on "star noise" as a thesis for his master's degree. The University of Wisconsin awarded him this degree on June 16, 1936.

Jansky made other contributions to the understanding of radio communications while he worked at Bell. He became adept at detecting the direction of arrival of short-wave transmissions from all over the globe, which led to a better understanding of the effects of radio propagation. The information Jansky gained helped refine the design of both transmitting and receiving antennas. He also conducted research on noise reduction in receivers and other circuits. The outbreak of World War II made it even more difficult for Jansky to pursue his research on "star noise." Still working for Bell Laboratories, he was assigned to a classified project concerning the development of direction finders for German U-boats or submarines. Jansky also worked on identifying particular transmitters by their "signatures," and his contributions led the military to issue him an Army-Navy citation. After the war, Jansky designed and developed frequency amplifiers which met the requirements of wide bandwidth and low noise.

Disappointed by the fact that he never had the time to investigate extraterrestrial radio waves further, Jansky applied for a teaching position at Iowa State University. He hoped that he would be able to use their facilities to further his research, but he was not hired. In 1948, the IRE made Jansky a fellow, but by this time Bright's disease was causing him to suffer from hypertension and heart problems. Although he tried to ward off the effects of his disease with specialized diets and health care, Jansky died at the age of 44 in 1950. He left behind his wife, Alice, to whom he had been married since August 3, 1929, and two children who were still teenagers.

Although never recognized for his contributions to radio astronomy during his lifetime, Jansky's work was honored 23 years later. In 1973, the General Assembly of the International Astronomer's Union adopted the Jansky as a unit of measurement. Defined as 1026 watts per meter squared hertz, the Jansky measures intensity of radio waves.

Jansky, Karl

views updated May 17 2018

Jansky, Karl (1905–50) US engineer, who discovered (1931) unidentifiable radio signals from space. He concluded that they were stellar in origin and that the source lay in the direction of Sagittarius. Jansky's discovery is considered to be the beginning of radio astronomy. The unit measuring radio emission is named after him.