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Karl Jansky and a New Age in Astronomy

Scoping out Radio Astronomy

A blog dedicated to telling the history of radio astronomy: its evolution, its discoveries, and its telescopes

Karl Jansky and a New Age in Astronomy

Olivia Wilkins

The beginning of regular trans-Atlantic radio telephony services in 1927—although a great stride in global communication efforts—was marked by increasing static interference. As receivers became more sensitive, they not only picked up communications but also unwanted background noise. The Bell Telephone Laboratories looked to investigate what caused this radio static and set up an experimental station at an abandoned potato farm in Holmdel, New Jersey. There, Karl Guthe Jansky (1905-1950), a young radio engineer, was given the task of constructing and operating a special antenna to find the cause of the static beginning in 1931.

Karle Guthe Jansky

Jansky's antenna was 100 feet long and able to slowly rotate (one revolution of the antenna took 20 minutes). The antenna could pick up a variety of radio waves, as well as provide characteristic information about the waves, such as their wavelengths. Jansky detected plenty of static, which he sorted into three categories—distant thunderstorms, nearby thunderstorms, and "static of unknown origin."

Jansky and his antenna in Homdel, New Jersey c. 1933 (National Radio Astronomy Observatory and Associated Universities, Inc.)

The unknown source was picked up as a steady, but weak, hiss with a wavelength of about 15 meters. Although the hiss was steady, it was not heard all the time. Because the hiss sometimes disappeared completely as Jansky rotated his antenna, he concluded that the source of this static was neither power lines nor radio transmitters, but something else.

Jansky's notebook showing the position and location of his antenna, 1935 (LSST)

Jansky kept thorough notes about the position of the source throughout the day. Initially, the source followed the sun: the static came from the east in the morning, the south at midday, and the west in the afternoon. After a month, however, the source of the static no longer aligned perfectly with the position of the sun, and after six months, the radio noise was coming from a point in the sky directly opposite the sun. Eventually, after a year, the source of noise realigned with the sun. From Jansky's observations, it was evident that the static was not coming from the center of our solar system.

The announcement of Jansky's radio detections published in the New York Times on May 5, 1933

On May 5, 1933, an article entitled "New Radio Waves Traced to Centre of the Milky Way" made the front page of The New York Times, highlighting the conclusion that Jansky's observations revealed radio emissions from a celestial source in the Milky Way outside our solar system. Although there had previously been speculations that emissions on the radio portion of the electromagnetic spectrum could be detected in space, Jansky's observations were the beginning of radio astronomy as a discipline. After publishing his findings, Jansky was reassigned to another project at Bell Labs. Despite the advent of a new age in astronomy, the discovery was quickly forgotten until it inspired radio amateurs to investigate further several years later.


  • New radio waves traced to centre of the Milky Way. The New York Times, 5 May 1933
  • Stokely, James. Atoms to Galaxies: An Introduction to Modern Astronomy. New York: Ronald Press, 1961, 37-39