In 1930 astronomers studied the heavens using only optical telescopes. Today things are very different and we now know that electromagnetic waves of different wavelengths from radio waves up to gamma rays are radiated by stars and other cosmic bodies, so we use a range of telescopes covering the whole spectrum. This change was instigated in 1931, not by a professional astronomer, but by an amateur and it took twenty years before the academics took notice.
Karl Jansky was a young radio engineer working for the Bell Telephone Labs who was tasked to look for sources of radio interference so that they could be eliminated from communication equipment. Jansky built a circular radio antenna some 30 meters in diameter that could be rotated on a platform and designed to pick up radio signals at 20 MHz. After some months he had identified different types of radio static including some that he understood to come from distant lightning storms, but another source was more enigmatic. He noticed that it repeated on a cycle of 23 hours and 56 minutes, the length of the sidereal day. This meant that it was coming from a fixed point against the stars and with more investigation he found that the strongest signal came from the centre of our galaxy.
The discovery was widely publicised and was even reported in the New York Times in 1933, yet professional astronomers did not see it as more than a curiosity. Jansky wanted to study the signal with a better purpose-built antenna, but times were hard and the Bell Labs were only interested in the practicalities of radio transmissions. Jansky’s application was rejected. Writing to his father in 1934 he said “I’m not working on the interstellar waves anymore. Friis has seen fit to make me work on the problems of and methods of measuring noise in general. A fundamental and necessary work, but not near as interesting as interstellar waves, nor will it bring near as much publicity. I’m going to do a little theoretical research of my own at home on the interstellar waves, however.”
The Great Depression was followed by World War II during which pure scientific research was put on hold while scientists contributed to the war effort. During that time another amateur engineer took up the cause of radio astronomy. Grote Reber built an impressive radio telescope dish in his back yard in 1937. He confirmed Jansky’s observations and drew up detailed contour maps of the signal strength which he published in the Astrophysical Journal.
Wanting to persue his research further, Jansky applied for a teaching post at Iowa State University hoping to make use of their facilities. Sadly however he was struck by illness and could not fulfill his dreams. He died in 1950 without seeing how important his pioneering research was about to become.
There were several reasons why it took so long for the importance of Jansky’s discovery to be recognised. The economic hardship and political unrest played its part, but in addition to that astronomers simply did not believe that the galaxy could be such a strong emitter of radio waves. This was not an observation they were willing to accept from amateurs at a time when professionals were concentrating on the revolutionary discoveries being made using optical instruments.
After the war radio astronomy gradually started to take off. In the US, John Krauss founded a radio observatory at Ohio State University, but it was Europe that took the first major lead. Bernard Lovell used equipment left over from the war to start a major project at Jodrell Bank in the UK. By 1957 he had built the giant radio dish 76 meters in diameter that would go on to revolutionise our knowledge of radio-active galaxies and the distant universe.
Karl Jansky did not live long enough to be honoured in his lifetime but posthumously he is accorded one of sciences most enduring forms of recognition. The metric unit for measuring the strength of radio sources is named the Jansky.