Karl Jansky: The Father of Radio Astronomy

Radio astronomy is the study of the radio frequencies emitted from stars, galaxies and other celestial objects. Radio waves are produced naturally from lightning and astronomical objects, or are produced by man-made communication techniques and broadcasting technology.Many radio telescopes are located around the globe and have helped discover new types of stars and galaxies that do not emit light and remain invisible to traditional telescopes. The catalyst for the birth of this new subfield in astronomy was a man often deemed the “father of radio astronomy”, Karl Jansky.

Image of Sag A

Jansky’s Legacy.3.6 cm radio emission  from the inner few parsecs of our Galaxy.The bright point source in the center is Sagittarius A*, which is likely a supermassive black hole at the center of the Galaxy.The mini-spiral of emission around the point source is from ionised gas that is in systematic motion about Sgr A*.(Image courtesy of NRAO/AUI )


Karl Guthe Jansky (1905-50) was born in Norman, Oklahoma; he was of French, Czech and English descent and grew up in Madison, Wisconsin.  Jansky was the third of six children and was named after physicist Karl Guthe whom his father Cyril Jansky had worked for earlier in his career.An interest in science and physics was perhaps in Karl’s genes as Cyril Jansky was a teacher who retired as a professor of Electrical Engineering at the University of Wisconsin.Karl Jansky’s eldest brother Cyril M. Jansky Jnr, also became a professor in radio engineering at the University of Minnesota.

Karl Jansky “Radio Astronomy, I am your father” (Image credit:Wikimedia.org)


Jansky joined Bell laboratories, New Jersey in 1928 after graduating from the University of Wisconsin with a degree in physics the previous year.He started his master’s degree immediately after his undergraduate degree but never completed it.Initially Karl Jansky was refused a position in the company until his brother Cyril, who was familiar with some members of the personnel department, persuaded them to take a chance on his little brother.  Bell Laboratories wanted to improve their radiotelephone service and Jansky was assigned the role of investigating the origins of static which was affecting trans-Atlantic radio transmissions.

Image of Karl_Jansky_radio_telescope

Jansky’s Merry-Go-Round (Image credit:Wikimedia.org)


In 1929, Karl Jansky began building an antenna to receive radio signals.This antenna system rotated, scanning the sky in 20 minutes , and gaining the nickname Jansky’s Merry-Go-Round.In the autumn of the following year his rotating short radio wave receiver was in working order.After recording signals for several months Jansky discovered three types of static.A weak signal caused by distant thunder storms, a more powerful burst due to local thunder storms and a third type which produced a steady hiss.In a 1933 journal article “Electrical Disturbances apparently of extra-terrestrial origin” Jansky refers to these electromagnetic waves detected causing the hiss to be coming from an unknown origin.

Jansky originally believed the steady hiss to be radiation coming from the Sun but after investigating this emission for over a year he discovered that the radio signal was not repeated every 24 hours like a solar day.Instead, it repeated every 23hours and 56 minutes , this was the same as a sidereal day, that is the time it takes for the stars to rotate across the sky (of course, they are really essentially stationary which the Earth rotates under them) .This discovery allowed Jansky to determine that the signal was not coming from our Solar System but instead from the centre of Milky Way in the direction of the constellation of Sagittarius.

This astonishing and uexpected discovery appeared in many publications including the New York Times in May 1933.Karl then proposed that Bell Laboratories build a 30 m dish antenna to study the galactic radio waves in more detail.During the 1930s the Great Depression had swept across America and funding a radical science project was not on the cards for another few years.Also, the original premise of his work was to discover the origins of static which he had achieved.Jansky then moved to a different department in Bell Labs measuring noise, but continued to investigate the stellar waves in his own time.He submitted his dissertation entitled ‘Star Noise’ which finally gained him his Masters degree in 1936.During the Second World War, Jansky worked in the development of direction finders to locate German submarines, and after the war he developed frequency amplifiers.

Karl Jansky died on Valentine’s Day, 1950 at 44 years old after suffering for years from Bright’s disease, a chronic kidney disease.  Jansky was diagnosed with kidney problems during his time at university and towards the end of his life; despite special diets he had high blood pressure and heart problems.His two children were still in their teens. Karl Jansky never had the opportunity to delve deeper into the study of interstellar radio waves.

However, despite never pursuing his keen interest into radio astronomy, Jansky is often recognised as the first person to discover these signals coming from outer space.He was fortunate during the time of research, in the early 1930s, that the Sun was going through an inactive period in its 11 year sun-spot cycle so detecting signals from further a field was easier.Otherwise the Sun’s radiation would have overwhelmed any other signals.Jansky’s findings inspired many other scientists such as Grote Reber who built his own radio telescope in 1937 and John Kraus who established a radio observatory after the war; both names now synonymous with Radio Astronomy.

Looking towards the centre of the Milky Way, a source of radio signals (Image credit:ESO)


Karl Guthe Jansky whilst just doing his normal job made a very important discovery in the realms of astronomy, despite never being an astronomer.

Discoveries of radio signals travelling from the centre of our galaxy inspired a new subfield of astronomy to be established and many subsequent discoveries to be made, which in turn justifies and explains that Karl Jansky should be the father of Radio Astronomy, he even has a unit named after him.

The unit of strength of radio sources is now known as the jansky.

(Article by Martina Redpath, Education Support Officer)