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.