[Previous] [Next] [Contents] [Home]

4. The History of Radio Astronomy

The early history of radio astronomy begins in 1894, with Sir Oliver Lodge. Lodge attempted detection of radiation from the sun at centimeter wavelengths. Unfortunately over the next forty years, further attempts also failed due to inadequate detection techniques.

The more recent history of radio astronomy begins in 1931 when an American engineer named Karl Jansky, while working for Bell Telephone Laboratories, conducted experiments on radio wavelength interference. Jansky detected three separate groups of static; local thunderstorms, distant thunderstorms and a steady hiss-type static of unknown origin. The unknown source that Jansky found is the center of the Milky Way as he was able to show by determining its position on the sky.

Jansky with early radio antenna

Jansky was the first to detect radio emission from the Galaxy. The image above shows Jansky standing with his antenna (Photo courtesy of Bell Laboratories). This rotatable antenna looks similar to a merry-go-round; the rotation allowed it to move along with the static. The work done by Jansky included receiving frequencies in the range of 15 to 30 MHz (approximately 15-m wavelengths). Jansky published three reports on his findings, which were largely ignored for many years to come. The field of radio astronomy would eventually recognize him with a unit named for him; the Jansky is equivalent to 10^(-26) watts per m^2 per Hz.

Reber with his radio antenna designIn 1937 Grote Reber, also a radio engineer, read about Jansky's work. Reber built a parabolic, 9.5-m diameter, reflector dish in his backyard. This was the first radio telescope used for astronomical research. Reber spent years studying cosmic radio waves at various wavelengths, while other astronomers still didn't get involved. He finally detected celestial radio emission at approximately 2-m. The image below shows Reber with his telescope, the prototype for modern radio telescopes (courtesy of NRAO). Reber continued his investigations of radio sources and confirmed that radio emission arose from the Galactic plane. Reber, in 1944, published the first radio frequency sky maps. Reber's telescope is displayed at the National Radio Astronomy Observatory (NRAO) in Green Bank West Virginia.

The first observation of radio emission from the sun was made in 1942, by J.S. Hey. Hey was working with the British Army Operational Research Group analyzing all occurrences of jamming of Army radar sets. A system for observing and recording jamming was organized. This eventually led Hey to conclude that the sun was radiating intense radio emission. Later that same year, G.C. Southworth made the first successful observations of thermal radio emission from the sun; he did this at centimeter wavelengths. The next important discovery regarding radio waves from beyond the solar system were discrete sources of emission. In 1946, J.S. Hey, S.J. Parsons, and J.W. Phillips observed fluctuations in the intensity of cosmic radio waves from the constellation Cygnus. In the next ten years thousands of discrete sources were identified, including galaxies and supernovae.

Most gases in galaxies are invisible to optical telescopes but can be seen by radio telescopes. Fast moving electrons, neutral atoms and molecules generously emit at radio wavelengths. In 1951, H. I. Ewen and E. M. Purcell, detected the spectral line emission from neutral Hydrogen that fell into the radio spectrum. For the first time, astronomers could determine the shape of our own home galaxy.

Panzias and Wilson with horn antennaIn 1963 Bell Laboratories assigned Arno Penzias and Robert Wilson the task of tracing the radio noise that was interfering with the development of communication satellites. Penzias and Wilson discovered that no matter where the antenna was pointed there was always non-zero noise strength, even where the sky was visibly empty. A simple solution would have been to reset their receivers to zero, but they persisted in tracing the source. This major discovery made by Penzias and Wilson was the cosmic background radiation and the strongest evidence for the big bang. Penzias and Wilson won the Nobel Prize in physics for their discovery in 1978. The image to the left shows Penzias and Wilson with their 6m horn antenna (Photo courtesy of Lucent Technologies, Bell Labs Innovation). The horn shape was used because the field of view remains unobstructed allowing for a precise measurement of the effective collecting area of the antenna.

In the late 1960's, radio pulsars, predicted only by theories of stellar evolution, were discovered by Jocelyn Bell-Burnell and Anthony Hewish. Bell-Burnell and Hewish were working at what is now called the Nuffield Radio Astronomy Observatory at Cambridge, England. Pulsars are very strongly magnetized, spinning neutron stars. Neutron stars are so dense that one teaspoon of this star would weigh as much as all the cars and trucks in the U.S. put together. Anthony Hewish and Martin Ryle won the Nobel prize for this discovery in 1974.

[Previous] [Next] [Contents] [Home]