Scientist

Karl Jansky

1905–1950 · Radio astronomy, engineering, physics
American radio engineer and founder of radio astronomy. His accidental discovery of cosmic radio emission in 1931 gave rise to a new way of exploring the Universe.

Biography

Born in 1905 in Norman, Oklahoma. He studied at the University of Wisconsin, earning a bachelor's degree in physics. He worked at Bell Telephone Laboratories, where he was tasked with investigating sources of radio interference. In the course of this work, he discovered a steady signal from the center of the Galaxy. Due to the priority of engineering over science at Bell Labs, he was not allowed to develop the discovery further, and he died young in 1950 without receiving widespread recognition. The unit of spectral flux density is named in his honor.

Key discoveries

💡 Jansky discovered cosmic radio emission while trying to find sources of noise for transatlantic radio communication. He built a rotating antenna, dubbed 'Jansky's merry-go-round', and initially thought he was hearing interference from cars, then from the Sun, until he realized the source moved with sidereal time.
"He said he could not believe that the signals came from beyond Earth, but all evidence indicated that their source is at the center of our Galaxy."
Concepts
cosmic microwave backgroundgalaxyinterstellar mediumradio astronomy
Scientists
Subrahmanyan ChandrasekharCharles TownesRalph AlpherAdam RiessJohn Archibald WheelerWilhelm WienLudwig BoltzmannRobert Woodrow Wilson

Related articles

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Interstellar Visitors: How to Catch a Signal from Alien Technology
In October 2017, the Pan-STARRS telescope in Hawaii spotted an object moving too fast to belong to the solar system. It was 1I/ʻOumuamua, the first interstellar visitor ever recorded by astronomers. Since then, two more have joined it: comet 2I/Borisov and object 3I/ATLAS.
High Energy2025-10-081 minarXiv:2510.07002express
Artificial Intelligence Unravels the Mysteries of Cosmic Radio Bursts
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Mission: Catch a Guest from Another Star System
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Catching an Interstellar Wanderer with a Solar Sling
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The Galaxy's Halo Is Lumpy: A Map from Hundreds of Radio Bursts
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Digital Twins Teach the CT Scanner
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How to Tell a Technical Glitch from a Real Disease
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Fossil Stars Found in Dwarf Galaxy
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Mysterious Flare from a Distant Galaxy
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How a cell decides whether to survive radiation
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Testing X-rays with sound
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Night Watchman for Cosmic Flashes
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High Energy2026-01-292 minarXiv:2601.21870express
A Radio Burst That Shouldn't Have Repeated
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Teaching a Neural Network to Read Textbooks
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A Christmas Tree on the Sun: How a Flare Paints a Pattern in Radio Waves
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How to Hear the Cosmos Through the Noise
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How Stars Kick Out Their Guests
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MeerKAT's Radio Ear Hears the Whisper of Solar Flares
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Galaxies2026-02-051 minarXiv:2602.05296express
How a Dwarf Galaxy Shook the Milky Way
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Blazar Flares: How to Tell Particle Accelerators Apart
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A Tissue Map from Blurry Images
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q-bio.QM2026-02-131 minarXiv:2602.12730express
How to See the Hidden Shapes of Proteins
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Ultrasound Keeps an Eye on the Spine
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Computer Vision2026-02-141 minarXiv:2602.13712express
AI Finds Worm Eggs in a Drop of Fluid
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Galaxies2026-02-182 minarXiv:2602.16766express
Lonely Dwarfs: How Astronomers Found 44 Isolated Galaxies
A population census, but instead of houses (galaxies, and instead of residents) stars. Astronomers set out to count the smallest and faintest "homesteads" in our cosmic neighborhood: dwarf galaxies. They are thousands of times fainter than the Milky Way, and spotting them in images is as hard as picking out a firefly in front of a spotlight.
Galaxies2026-02-191 minarXiv:2602.17652express
Tiny Systems on the Edge of the Milky Way
On the outskirts of the Milky Way, tiny stellar systems hide, so faint that even powerful telescopes barely spot them. Until recently, astronomers knew almost nothing about these objects, dubbed ultra-faint compact satellites.
Stellar2026-02-231 minarXiv:2602.19836express
Longer Loop, Slower Flare
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Stellar2026-02-232 minarXiv:2602.20311express
Stellar Flares Ignite Each Other
The Sun occasionally produces flares — powerful bursts of energy that last from minutes to hours. Most are random, like raindrops hitting a roof. But sometimes one flare seems to ignite another: the second begins almost immediately after the first, even though they occur in different locations. Astronomers call these sympathetic flares.
Galaxies2026-02-252 minarXiv:2602.21875express
Cosmic Fluff: Galaxies Without Bright Light
In 2015, astronomers were examining the Coma galaxy cluster and noticed something odd: huge, almost invisible "fluff balls." These galaxies are as large as our Milky Way but shine hundreds of times fainter.
High Energy2026-02-251 minarXiv:2602.22309express
Radio Burst Reveals the Secret of a Newborn Supernova
Fast radio bursts are instantaneous radio flashes from deep space. In a thousandth of a second they release as much energy as the Sun emits in a month. One such burst, repeating, allowed scientists to peer into the epicenter of a recent stellar explosion.
Stellar2026-02-271 minarXiv:2602.24250express
Caught in the Act: Solar Storms of the 1940s
In the 1940s, long before modern sensors, instruments on Earth were already catching particles from space. When a powerful flare erupted on the Sun, it ejected a stream of charged particles — solar energetic particles.
Exoplanets2026-02-282 minarXiv:2603.00782express
An Interstellar Visitor: How a Comet Revealed Its Temperament
Comet 3I/ATLAS is a rare guest: it came from interstellar space, from another star. As it passed near the Sun, ice on its surface began to sublimate, and gas jets acted like tiny rocket engines. This force, called non-gravitational acceleration, nudges the comet off a purely gravitational trajectory.
q-bio.CB2026-02-281 minarXiv:2603.00834express
How Skin Cells Close a Wound: A Dance of Division and Movement
When you cut your finger, skin cells start working in concert: some divide, others crawl toward the wound, and still others pause. But exactly how a cell decides what to do next depends on its internal "schedule"—the cell cycle.