Also known as: Karl Jansky, Jansky
Karl Jansky (1905–1950) was an American physicist and radio engineer at Bell Telephone Laboratories who, while tracking down sources of static on transatlantic radio links, discovered that the Milky Way itself emits radio waves — founding the science of radio astronomy.1 His careful separation of a persistent cosmic hiss from terrestrial and atmospheric interference remains a model of how to read signals buried in the noise floor.
Life and work
Jansky was born in 1905 in what is now Oklahoma and studied physics at the University of Wisconsin. In 1928 he joined Bell Labs, which assigned him to investigate the sources of static that degraded shortwave radiotelephone service across the Atlantic. To do this he built a large steerable antenna — a rotating array nicknamed “Jansky’s merry-go-round” — tuned near 20.5 MHz and mounted on a turntable so it could find the direction of incoming interference.1
Cataloguing the static, he identified two familiar culprits: nearby thunderstorms and distant thunderstorms carried in by the ionosphere. But a third, faint, steady hiss puzzled him. It rose and fell once a day — but not exactly on the 24-hour solar cycle.
Contribution
By 1932 Jansky had established that the mystery hiss repeated every 23 hours and 56 minutes, the length of the sidereal day, meaning its source was fixed against the stars rather than the Sun. He traced its peak to the constellation Sagittarius, toward the center of the Milky Way. He had detected radio emission from our own galaxy — the first astronomical object ever observed at radio wavelengths.1 The discovery meant that the sky could be studied in a band of the spectrum far below visible light, and that a natural cosmic contribution sits beneath every terrestrial receiver’s noise floor.
Legacy
Bell Labs had no interest in pursuing astronomy, and Jansky moved on to other work; he died young, in 1950, of a heart condition. His discovery lay largely dormant until amateur Grote Reber built the first dedicated radio telescope later in the 1930s, and radio astronomy blossomed after World War II into a field that mapped pulsars, quasars, and the cosmic microwave background. The unit of spectral flux density used throughout radio astronomy — the jansky (Jy) — is named in his honour, a fitting measure for a career spent quantifying the faintest signals in the sky.
Sources
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Karl Guthe Jansky — Wikipedia, for biography, the merry-go-round antenna, and the discovery of galactic radio emission. ↩ ↩2 ↩3