About the Observatory
Founded in 1956, the NRAO provides state-of-the-art radio telescope facilities for use by the international scientific community. NRAO telescopes are open to all astronomers regardless of institutional or national affiliation. Observing time on NRAO telescopes is available on a competitive basis to qualified scientists after evaluation of research proposals on the basis of scientific merit, the capability of the instruments to do the work, and the availability of the telescope during the requested time. NRAO also provides both formal and informal programs in education and public outreach for teachers, students, the general public, and the media.
The NRAO is funded by the National Science Foundation (NSF) under the terms of a cooperative agreement between the NSF and Associated Universities, Inc. (AUI), a science management corporation.
The NRAO operates a complementary suite of powerful telescopes for exploring the Universe:
- Robert C. Byrd Green Bank Telescope (GBT), the world’s most sensitive single-dish radio telescope.
- Karl G. Jansky Very Large Array (VLA), an array of 27 radio telescopes that is among the most productive research tools in astronomy.
- Very Long Baseline Array (VLBA), an array of 10 radio telescopes and the highest resolution astronomical telescope.
- Atacama Large Millimeter/submillimeter Array (ALMA), a partnership with Europe, Japan, and Chile that will be available to the U.S. and Canadian astronomical communities through the North American ALMA Science Center (NAASC).
Detection of the radio waves emitted by astronomical objects demands technology and signal processing that push the state-of-the-art. The scientists and engineers of the NRAO Central Development Laboratory perform much of the innovative research and development that yields the required instrumentation and processing advances.
Why a National Radio Astronomy Observatory?
For quite a long time, observers of the sky had no evidence that the Universe was giving off anything more than optical light. In the 1800s, scientists discovered ultraviolet and infrared radiation coming from the Sun. It wasn’t until Karl Jansky’s 1933 discovery of radio waves coming from the center of our Milky Way Galaxy that scientists were made aware of an entirely invisibly-radiating Universe awaiting telescopic exploration.
The intervening years of the Great Depression and the Second World War stalled the advancement of the new field of radio wave astronomy. However, a young engineer named Grote Reber kept Jansky’s fire burning in the United States by building his own radio telescope and making significant discoveries of new bright radio sources beyond our Milky Way.
When the War ended, scientists around the world were able to reveal profound discoveries they had made while they were soldiers scanning the skies for enemy signals. The greatest example comes from English physicist James Stanley Hey who led a team of scientists as a radar research group during the War. In 1942, he wrote a secret research paper about what he had first suspected was a new kind of enemy jamming radar, but which turned out to be radio waves from an incredible flare from the Sun. In 1945, he was finally able to publish this discovery in the prestigious journal Nature.
War’s end also provided the world’s scientific communities with dozens of discarded radio antennas and radar devices. From the radio portraits of the Sun, measuring of meteor showers, and the still-in-use Cambridge sky surveys of “radio stars,” revolutionary publications began appearing in research journals across Europe, Japan, and the Soviet Union.
Post-War American Astronomy
In the United States, optical astronomers had access to the world’s most powerful telescopes, were making plenty of their own discoveries, and were not versed enough in the engineering techniques of the radio community to want to branch into it. In fact, historical accounts show that the two research communities did not mix well, with the optical community believing itself to be the “real astronomers.”
Immediate post-War science funding was guided by committees of optical astronomers who were hesitant about investing in a field that its experts had not embraced. So, radio wave observations of the Universe were confined to the special interest groups funded at the discretion of individual departments at isolated institutions.
Nonetheless, American engineers and physicists at the Naval Research Laboratory, the Massachusetts Institute of Technology, and Cornell University were active in radio and radar explorations in the 1940s, particularly of the Sun and Moon. Ohio State University, the Carnegie Institute of Washington, and Stanford University later began their own impressive radio studies.
In Australia and Europe, impressive experiments in multiple antenna design were improving the detail with which radio instruments could map the hidden Universe. Sydney scientists used the reflection of radio waves on the ocean below as a second antenna to pair with one on an overlooking cliff. The interference patterns created by combining the two waves shrunk the beam – which in radio terms means it focused their sky view to finer detail. This technique is called interferometry.
In Cambridge, England, scientists combined signals from a range of antennas in a field to simulate a larger, single telescope in 1946. This method is called aperture synthesis, and it became the lynchpin for radio astronomy’s detailed imaging capabilities to match those of optical astronomy – with an array, the resolution of a radio telescope can equal or better the resolution of a large optical telescope.
Martin Ryle and Anthony Hewish of the University of Cambridge in England won the Nobel Prize in Physics for this critical development. Their invention paved the way for future radio telescopes to produce detailed images of radio sources, which finally persuaded optical astronomers to recognize the cosmic radio wave pursuit as a form of astronomy.
Founding of the NRAO
In 1951, Harvard physics graduate student Harold Ewen and his advisor, Edward Purcell, discovered the radio signal of hydrogen coming from the spaces in between the stars of our Galaxy. Hydrogen was radiating from everywhere, ready to be mapped and measured by radio telescopes. What else was profoundly waiting for discovery?
Bart Bok, Harvard Astronomy Department Head, recognized the science that was being learned by radio wave observations of the Cosmos. He started the first radio astronomy graduate degree program, and in 1954, went on to champion the need for a national radio astronomy facility funded by the United States government. No single university or organization could manage the scale of facility required to create the kind of radio telescopes that would be of the same caliber as our optical ones.
Bok and the astronomy leaders of several major research universities convinced Associated Universities, Incorporated, an organization founded to manage the United States’ first national science facility, the Brookhaven National Laboratory. By 1955, the National Science Foundation had provided funds for a feasibility study, and on November 17, 1956, a five-year contract was signed between AUI and the NSF for a National Radio Astronomy Observatory.
Selection of the first Observatory site was tough and took nearly a year. The high, wide valley of Green Bank, in West Virginia, was chosen for its lack of city radio interference, its proximity to AUI and NSF headquarters in Washington, D.C., and its middle-latitude location to allow view of the center of our Galaxy but also northern observations of aurorae and other polar atmospheric effects.
The National Science Foundation broke ground on the Green Bank site on October 17, 1957. In November, we had set up a simple dipole antenna on the site, and radio frequency interference protection was initiated. By 1962, we were operating the world’s largest moving telescope: a 300-foot parabolic dish. By 1965, the biggest equatorially-mounted telescope in the world was hunting molecules across our Galaxy.
Suite of Telescopes Under Open Skies
During the 1960s we designed and built the molecule-hunting millimeter telescope in Tuscon, Arizona and in 1980 opened the Very Large Array in New Mexico. In the 1990s, we set up the ten stations of the Very Long Baseline Array and planned a large-scale millimeter/submillimeter array that later became the international project known as the Atacama Large Millimeter/submillimeter Array sited in Chile.
As a national facility, the NRAO has achieved the goal of providing the United States with cutting-edge instruments for the exploration of the hidden Universe of radio wavelength radiation. Our telescopes remain the best of their class in the world, open to scholarly proposal-based observing from scientists around the world, and we make our technologies available for others to benefit from our expertise.