The National Radio Astronomy Observatory
Founded in 1956, the National Radio Astronomy Observatory (NRAO) is one of the world's premier research facilities for radio astronomy. NRAO operates powerful, advanced radio telescopes spanning the western hemisphere. Scientists from around the world use these instruments to probe fundamental questions in astronomy and physics.
NRAO is a research facility of the U.S. National Science Foundation and acts as a national facility providing state-of-the-art radio telescopes and support instrumentation for use by the entire scientific community. NRAO designs, builds, operates and maintains radio telescopes that are used to study virtually all types of astronomical objects known, from planets and comets in our own Solar System to quasars and galaxies billions of light years away.
NRAO has its headquarters in Charlottesville, VA, and operates major radio telescope facilities at Green Bank, WV; Socorro, NM; and Tucson, AZ. The NRAO is operated for the National Science Foundation by a consortium of universities known as Associated Universities, Inc., under a cooperative agreement.
Major instruments at Green Bank include the largest fully steerable radio telescope in the world, named the Robert C. Byrd Green Bank Telescope (GBT). A 140-foot equatorially mounted radio telescope on the site was decommissioned in 1999, and a host of smaller instruments.
[Information adapted from NRAO website materials]
The Robert C. Byrd Green Bank Telescope.
[adapted from the NRAO website for the Green Bank Telescope (GBT)]
The GBT is described as a 100-meter telescope, but the actual dimensions of the surface are 100 x 110 meters. The overall structure of the GBT is a wheel-and-track design that allows the telescope to view the entire sky above 5 degrees elevation. The track, 64 m (210 ft) in diameter, is level to within a few thousandths of an inch in order to provide precise pointing of the structure while bearing 7300 metric tons (16,000,000 pounds) of moving weight.
The GBT is of an unusual design. Unlike conventional telescopes, which have a series of supports in the middle of the surface, the GBT's aperture is unblocked so that incoming radiation meets the surface directly. This increases the useful area of the telescope and eliminates reflection and diffraction that ordinarily complicate a telescope's pattern of response. To accommodate this, an off-axis feed arm cradles the dish, projecting upward at one edge, and the telescope surface is asymmetrical. It is actually a 100-by-110 meter section of a conventional, rotationally symmetric 208-meter figure, beginning four meters outward from the vertex of the hypothetical parent structure.
The GBT's lack of circular symmetry greatly increases the complexity of its design and construction. The GBT is also unusual in that the 2,004 panels that make up its surface are mounted at their corners on actuators (little motor-driven pistons) which make it easier to adjust the surface shape. Such adjustment is crucial to the high-frequency performance of the GBT in which an accurate surface figure must be maintained.
Other NRAO Sites:
The Very Large Array (VLA), located on the Plains of San Agustin, 60 miles west of Socorro, New Mexico, was depicted in the movie Contact starring Jodie Foster. The interferometric array consists of 27 antennas, each measuring 25 meters (81 feet) in diameter and weighing approximately 200 tons. The Very Long Baseline Array (VLBA), remotely controlled from the Array Operations Center in Socorro, New Mexico, is comprised of ten radio telescopes which work together as the world's largest, dedicated full-time astronomical instrument. The newest telescope project of the National Radio Astronomy Observatory is the Atacama Large Millimeter Array (ALMA) Project. This endeavor includes the collaboration of observatories from around the world in the manufacturing of 64 12-meter antennas. The site is located at an elevation of 16,400 feet in Llano de Chajnantor, Chile.