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Your
Engineering Heritage
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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.
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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