Green Bank Telescope
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| Green Bank Telescope | |
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| Organization | NRAO |
|---|---|
| Location | Green Bank, West Virginia, USA |
| Coordinates | Coordinates: |
| Wavelength | radio |
| Built | 1991-2002 |
| First light | August 22, 2000 |
| Telescope style | Parabolic off-axis reflector, Gregorian optics |
| Diameter | 100m |
| Collecting area | 7,854m2 |
| Focal length | 60 m |
| Mounting | wheel and track mount |
| Website | www.gb.nrao.edu/GBT/GBT.shtml |
The Robert C. Byrd Green Bank Telescope (GBT) is the world's largest fully steerable radio telescope and the world's largest land-based movable structure. It is part of the National Radio Astronomy Observatory (NRAO) site at Green Bank, West Virginia (USA). The telescope honors the name of Senator Robert C. Byrd.
The telescope was built following the collapse of the previous Green Bank telescope, a 300ft paraboloid. This telescope collapsed on 15 November 1988 due to the sudden loss of a gusset plate in the box girder assembly, which was a key component for the structural integrity of the telescope.[1]
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[edit] Location
The telescope sits at the heart of the United States National Radio Quiet Zone, a large area where all radio transmissions are either limited or banned outright, to help the telescope function properly.
[edit] Description[2]
The surface area of the GBT is 100 by 110 meters with 2,209 actuators (a small motor used to adjust the position) for the 2,004 surface panels. The panels are made from aluminium to a surface accuracy of less than 0.003 inches (76.2 micrometers) RMS. The actuators adjust the panel positions to correct for distortions due to gravity which change as the telescope moves. Without this so-called "active surface", observations at frequencies above 4 GHz would not be as accurate.
The telescope is unusual in that the mirror is not a symmetrical dish, but is a section of a much larger parabolic figure with the receiver where the prime focus of the entire mirror would be. As a result, the support for the receiver does not in any way obscure the mirror's view of the sky.
The offset support "arm" houses a retractable prime focus feed horn in front of the 8 m subreflector and eight higher-frequency feeds on a rotating turret at the Gregorian focus. Operational frequencies range from 290 MHz to 49.8 GHz.
The telescope is equipped with a special laser system where beams of light are reflected inside the dish. Monitoring of these beams shows how the telescope image may be distorted by gravity, wind, etc. This shows the researchers how to adjust the surfaces to make up for the distortion.[3]
[edit] Image Gallery
 The GBT from the distance of the NRAO visitor's center |
 The GBT with people for scale |
 Azimuth track which supports the weight of the entire telescope |
 Close-up of the azimuth track |
 Underneath the GBT dish |
 Altitude wheel and track |
 Counterweights on the altitude track |
 Painter painting the GBT structure |
 Elevator to the receiver room |
 Prime focus receiver in front of the secondary reflector |
 Feed horns for various receivers |
[edit] See also
[edit] References
- ^ NRAO 300 foot Telescope Home Page
- ^ Toney Minter (May 2007). The Proposer’s Guide for the Green Bank Telescope (PDF). NRAO. Retrieved on 2007-07-14.
- ^ The Robert C. Byrd Green Bank Telescope
