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ArrowKarl Jansky (1905-1950)

Karl Jansky

Karl Jansky, often referred to as the father of radio astronomy, was born on October 22, 1905 in Norman, Oklahoma. He was one of six children born to Nellie Jansky and Cyril Jansky, from whom he and his three brothers acquired an interest in physics at a young age. Cyril Jansky was a professor of electrical engineering and Dean of the College of Engineering at the University of Oklahoma before later accepting an appointment at the University of Wisconsin. It was in Wisconsin that Karl Jansky began his formal education. Following his public school years, he entered the state university, where he embarked on a study of physics. Jansky received a B.S. degree in 1927, graduating with honors. He remained at the university for an extra year as an instructor and completed coursework towards a graduate degree, but did not receive the degree at that time because he did not write a thesis.

Jansky began working at Bell Laboratories in 1928, despite the company’s initial hesitation to hire him due to his health problems (Jansky had been diagnosed with chronic kidney disease in college). At Bell, he was assigned to a project investigating possible sources of interference in shortwave radio communications across the Atlantic. To embark on this study, it was necessary for Jansky to design special instrumentation. The large, directional antenna system he built to receive radio waves was mounted on a motor-driven turntable so that it rotated in all directions, resulting in it being nicknamed Jansky’s merry-go-round. In addition to this device, he designed a receiver that minimized static and an apparatus for recording static variations. The new equipment was set up in Holmdel, a rural part of New Jersey, in 1930, and soon after the task of collecting data began.

Jansky spent many months recording the characteristics and intensity of static his instrumentation received, most commonly at a wavelength of 14.6 meters. In 1932, he reported his early findings and classified the static into three basic types. The first he attributed to local thunderstorms, the second to distant thunderstorms, and the third type, as he described it, was “composed of very steady hiss static the origin of which is not yet known.” Jansky had already at that point, however, begun to understand where the static was coming from, though he had been warned by his boss to be careful in declaring the information in case he proved to be wrong. The caution advised at Bell was understandable because Jansky believed the signal was coming from the center of the Milky Way galaxy and no one had ever detected extraterrestrial signals before.

The first clues that the static in question was extraterrestrial were revealed to Jansky during his study of its intensity, which peaked when the antenna was positioned so that it pointed at a particular part of the sky. Initially Jansky believed the point of the peak intensity to be following the sun and, thus, thought the sun might be the source of the signal. Over time, however, the peaks appeared to increasingly deviate from the path of the sun and he realized that they occurred not every 24 hours, as would be expected if the sun was the signal’s source, but rather every 23 hours and 56 minutes. When he discussed the phenomenon with an acquaintance who had a background in astronomy, he was made aware that the four minute variation was characteristic of sidereal time, that is, time determined by the apparent daily motions of the stars. The sidereal day is shorter than the solar day because it is based solely on the amount of time required for the Earth to make a single rotation about its axis, whereas the solar day depends on this rotation as well as the Earth’s orbit around the sun. This information, along with data indicating that the emission was coming from the direction of the constellation Sagittarius, enabled Jansky to firmly conclude that the mysterious signals were coming from space.

In 1933, Jansky published three papers outlining the data he obtained regarding the hissing static and the conclusions that he drew from the data. Two years later, he further hypothesized that the radiation most likely developed in interstellar space due to the thermal motion of charged particles. Interestingly, the scientific community seems to have at first taken less notice of Jansky’s work than did the general public, which was made aware of the extraterrestrial radio waves in the headlines of the New York Times on May 5, 1933. Indeed, no academic or research institutions immediately followed up on Jansky’s discovery, so that the next person to detect cosmic signals was Grote Reber, who constructed a radio telescope in his Illinois backyard in 1937 for his own personal use. Notably, Jansky had wanted to continue studying the radio waves he discovered himself and had tried to convince his employer to construct a dish antenna with a diameter of 30 meters for him to do so. Bell, however, was understandably only interested in the matter as far as it pertained to their communications business, and since there was no way to eliminate the hissing static, they considered the project complete. Jansky was, therefore, quickly assigned to new tasks.

The University of Wisconsin accepted Jansky’s published papers on radio waves as his thesis and finally awarded him his M.S. degree in 1936. In 1948 he was made a fellow of the Institute of Radio Engineers. Otherwise, Jansky received few official honors during his lifetime related to his discovery, which opened an entirely new field of science. He remained at Bell Labs for the rest of his career, and there continued to contribute to improved radio communications. On February 14, 1950, he died of a massive stroke linked to his kidney disease. His wife, Alice, and two children survived him.

More than two decades after his death, the General Assembly of the International Astronomer's Union adopted the jansky as a unit of measurement for radio wave intensity as a tribute to Karl Jansky. Bell Labs later erected a monument to Jansky at the New Jersey site where he had carried out his groundbreaking study. The monument’s dedication ceremony took place in 1998.


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