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December 2002

 
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Your Engineering Heritage

Arecibo Observatory
Photo: IEEE History Center

Arecibo Observatory

The Beginnings of Radio Astronomy

by Frederik Nebeker

In 1925, just a dozen years after engineers learned to generate radio waves using an electron tube, Gregory Breit and Merle Tuve, working for the Carnegie Institution of Washington D.C., bounced radio waves off the ionosphere and thus determined its height. This showed that radio waves could be used as probes. Two years later, in a Radio News article titled “Can We Radio the Planets?” well-known radio enthusiast and popularizer Hugo Gernsback proposed that radio waves be bounced off the moon and planets. Furthermore, he calculated the time for a signal to travel to the moon and back to be 2.5 seconds.

In the early 1930s at Bell Telephone Laboratories, Karl Jansky was investigating the noise in the radiotelephone transmissions across the Atlantic Ocean. He distinguished three types of static: crashes from local thunderstorms, a steadier and weaker static from the combined effects of distant storms, and a weak hiss of unknown origin. It was 70 years ago this month that he first reported these results (in an article in Proceedings of the IRE), suggesting that the weak hiss might be associated with the sun. Continuing his research using a highly directional antenna, Jansky soon gathered evidence that the disturbances, in fact, came from outside the solar system, with one source being the center of the Milky Way galaxy.

One might imagine that, widely reported as they were, such results would initiate a new branch of astronomy. But Bell Labs rejected Jansky’s request to build a 100-foot antenna, and he was given other assignments. No academic institutions followed up on his work. In fact, until after World War II, apparently the only person who did was Grote Reber, a radio engineer in Wheaton, Illinois, who pursued it as a hobby in his spare time. Reber built a 31-foot parabolic antenna and in 1937 made the first radio maps of the sky.

The intense development of radar during World War II greatly advanced the techniques needed for radio astronomy. In 1945, Arthur C. Clarke published an article on "The Astronomer’s New Weapons — Electronic Aids to Astronomy." In the article, he discussed the possibility of using radar to probe the planets. An obvious first step was radar detection of the moon, and in early 1946 two groups succeeded: a U.S. Army Signal Corps team headed by J.H. De Witt saw echoes of the moon on a cathode ray tube; and Z. Bay in Hungary, in an ingenious but less direct manner, obtained evidence of echoes of the moon.

In the late 1940s and early 1950s, radio astronomy finally emerged as a new branch of astronomy. Taking the lead were groups from Manchester University; Cambridge University; and the Australian Commonwealth Scientific and Industrial Research Organisation. Though radar continued to be developed for investigating meteors and planets, the principal mode of investigation was the mapping of distant radio sources. A 76-meter steerable radio-telescope was completed at Jodrell Bank, England, in 1957, and a 305-meter fixed reflector was completed in Arecibo, Puerto Rico, in 1963. This Arecibo reflector is now an IEEE Milestone in Electrical Engineering and Computing.

 

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Frederik Nebeker is Senior Research Historian at the IEEE History Center at Rutgers University in New Brunswick, N.J. Visit the IEEE History Center's Web page at: www.ieee.org/organizations/history_center/.

 

 

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