National Radio Astronomy Observatory

The National Radio Astronomy Observatory, or NRAO, maintains the most extensive facilities for radio astronomical observations in the United States. First established in 1956, the NRAO has become one of the preeminent institutions for radio astronomy research and technology worldwide.


History

The NRAO grew from a conference held in Washington in January of 1954, to discuss the development and expansion of radio astronomy in the United States. Radio astronomy was to some extent born in the United States, with the discovery of celestial radio waves by Karl Jansky. However, as an organized science, radio astronomy in the U.S. soon lagged behind many other countries (especially the United Kingdom). Several individual universities had good radio astronomy facilities (like the University of Michigan, and Grote Reber's observatory at Ohio State University). And the government, too, had initiated some work in this field, particularly though the work of the Naval Research Laboratory (NRL). However, at the 1954 conference, it became apparent that major increases in radio astronomy technology and capability would require a major investment in capital, more than could or should be made by individual universities or organizations. So the commitee organizers drafted a plan for a national observatory, to be run independently of individual universities, which could be used by astronomers throughout the United States. After receiving funding for their organization from the National Science Foundation in 1956, the Associated Universities, Incorporated (an umbrella organization of several US research Universities) founded the National Radio Astronomy Observatory, NRAO, in 1956.


Telescopes

Green Bank -- the original site

NRAO built their first telescope -- the 85-foot Howard E. Tatel telescope -- in Green Bank, West Virginia near a site originally selected for use by the NRL. The telescope became operational in 1959, and was the first of many telescopes to be built by the NRAO around the country. NRAO was originally headquartered at the Green Bank site, but the staff were eventually moved about 60 miles east to their current headquarters at Charlottesville, VA. However, the Green Bank site is still the main "observatory" where observations are conducted. The original 85-foot telescope was converted to a 3-element interferometer in the mid-1960's, and the observatory site was expanded to include 140-foot and 300-foot radio dishes. (The original 300-foot dish unfortunately collapsed in 1988, and was replaced with the 100-meter Robert C. Byrd Green Bank Telescope in 2000.)

Kitt Peak

NRAO maintains several other astronomical observatories throughout the United States, in addition to facilities at Green Bank. The first outside of West Virginia was a 36-foot millimeter-wave (60-300 GHz) telescope on Kitt Peak in southern Arizona, which was already the site of several optical telescopes. This telescope was designed to operate at much higher frequencies than those at Green Bank to detect molecules in space, and was for many years the only telescope in the United States to conduct millimeter-wavelength astronomy. It was placed on Kitt Peak because the air in southern Arizona is very dry, which reduces the interference from water molecules in our atmosphere. Although it was built and operated by NRAO for many years, control of the telescope was recently transferred to the Steward Observatory of the University of Arizona. (It was also rebuilt in 1984, and as a result is now 12-meters, or 39.2-feet, in diameter).

The Very Large Array -- VLA

However both of these facilities are certainly overshadowed in the minds of the public by the Very Large Array or VLA, a network of 27 20-meter steerable radio dishes laid out on the Plains of San Augustin, near Magdalena, New Mexico. The VLA was proposed in the late 1960's and early 1970's as a new facility for radio interferometry -- the technique of electronically coupling individual, small telescopes so that they would act like a single, giant telescope with an effective diameter equal to the maximum separation of the individual telescopes. The VLA would be nearly 36 kilometers across when completed. NRAO was granted over $73 million by the US Congress in 1972 for the VLA, and construction was begun a year later. The full observatory took seven years to build, though parts were in operation as early as late 1975, and the first successful interferometric test was conducted on February 18, 1976. The VLA remains to this day one of the finest radio astronomy observatories in the world.

You may have seen the control room of the VLA before: footage of the VLA in the film Contact were really filmed on site at the VLA -- it looks exactly the same in real life. Be aware, however, that you will probably get a stern talking-to if, like Jodie Foster, you tried to use a walkie-talkie in close proximity to one of the dishes during an observation -- too much RFI! The VLA site hosts a small-but-interesting visitor center, and if you call in advance (and have a good reason like bringing a school or scouting group), you might be able to schedule a guided tour of both the array antennas and the VLA control center itself.

The Very Long Baseline Array -- VLBA

The final "telescope" of the NRAO is the Very Long Baseline Array or VLBA, used for Very Long Baseline Interferometry (VLBI). Like the VLA, the VLBA is an interferometric telescope, but on a far, far larger scale. The VLBA uses a network of telescopes throughout the western hemisphere, with locations from Hawaii to St. Croix, USVI. Unlike the VLA, where telescopes were originally connected via waveguides into a single instrument, data for VLBA observations are recorded onto data tape, and then combined using a computer to obtain interferometric images. The VLBA can obtain measurements with angular sizes smaller than a milliarcsecond (that's less than one millionth the diameter of the full moon), and has observed everything from the pulsations of Mira stars to the movement of radio jets in quasars on the other side of the universe. The VLBA is "headquartered" in the Array Operations Center in Socorro, New Mexico which also houses the staff science center for the VLA. The Socorro office is located on the campus of New Mexico Tech (a very pretty place, especially in the autumn).

(It is worth noting that NRAO does not operate all of the radio observatories in the United States. Notable exceptions include Cornell University's Arecibo Observatory, CalTech's Owens Valley Radio Observatory, and the Berkley-Illinois-Maryland Association (BIMA) Array. Arecibo is a huge telescope built into a natural depression in a mountain in Puerto Rico. The latter two observatories are interferometers used for millimeter wavelength astronomy.)


Other projects, and the future

The NRAO is involved in several other projects. First, it has been the primary developer of the Astronomical Image Processing Software or AIPS package, which is used to analyze radio interferometric data. NRAO is also a major partner in the Atacama Large Millimeter Array, or ALMA Project -- a millimeter-wave, interferometric facility under construction in the Chilean Andes. They also participate in many VLBI projects with collaborators around the world, combining VLBA telescopes with similar facilities in Japan, Australia, the United Kingdom, and the Netherlands to obtain even more sensitive observations. They are also an important lobbying organization which tries to reduce the impact of terrestrial radio interference on radio astronomy worldwide.


Sources:
Several websites of the NRAO, all of which can be found through www.nrao.edu.
I also found some historical information in The History of Radio Astronomy by J.S. Hey (Science History Publications: New York, 1973).
Finally, I also made many personal visits to Socorro and the VLA over the years -- a perk of going to school in New Mexico.

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