Karl Jansky Detects Radio Waves From the Milky Way
A Bell Labs engineer chasing static in phone lines accidentally opens a new window on the universe
Quick facts
- Discoverer
- Karl Jansky, Bell Telephone Laboratories
- Year of discovery
- 1932
- Source identified
- Center of the Milky Way, constellation Sagittarius
- Public announcement
- New York Times, May 1933
What happened
In 1932, Karl Jansky, an engineer at Bell Telephone Laboratories in New Jersey, revealed that stars and other objects in space radiated radio waves, a discovery he made while investigating the sources of static interference plaguing transatlantic radiotelephone communications. Jansky built a large directional antenna to track down the interference and eventually linked the source of a persistent, unexplained hiss to something in the sky rather than to any terrestrial cause, identifying the source as the center of the Milky Way galaxy in the constellation Sagittarius. Jansky's finding was announced on the front page of the New York Times in May 1933 and marked the beginning of radio astronomy as a field distinct from traditional optical observation of the night sky.
Why it matters
Jansky's accidental discovery proved that celestial objects emit far more than visible light, opening an entirely new part of the electromagnetic spectrum to astronomical study. Radio astronomy that grew from his work would go on to discover pulsars, quasars, and, three decades later at the very same Bell Labs, the cosmic microwave background radiation left over from the Big Bang.
How we know
Jansky published his findings in the paper Radio Waves from Outside the Solar System in 1933, and his original antenna and data are documented in Bell Labs' own institutional records alongside the contemporary newspaper coverage of the discovery.
Sources
- NASA Science. Radio Waves · Reputable sourcescience.nasa.gov · The domain "science.nasa.gov" is on our Reputable source registry. · Link is live and its text matches the event's key terms (Jul 2026)
- NASA Goddard Space Flight Center, Cosmic Times. Radio 'Ear' on the Universe Being Built · Reputable sourceimagine.gsfc.nasa.gov · The domain "imagine.gsfc.nasa.gov" is on our Reputable source registry. · Link is live and its text matches the event's key terms (Jul 2026)
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