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Green Bank Telescope

100m Robert C. Byrd Green Bank Telescope

The Robert C. Byrd Green Bank Telescope, or GBT, is the world’s premiere single-dish radio telescope operating at meter to millimeter wavelengths. Its enormous 100-meter diameter collecting area, its unblocked aperture, and its excellent surface accuracy provide unprecedented sensitivity across the telescope’s full 0.1 – 116 GHz (3.0m – 2.6mm) operating range.

The single focal plane is ideal for rapid, wide-field imaging systems – cameras. Because the GBT has access to 85% of the celestial sphere, it serves as the wide-field imaging complement to ALMA and the EVLA. Its operation is highly efficient, and it is used for observations about 6500 hours every year, with 2000-3000 hours per year available to high frequency science.

Part of the scientific strength of the GBT is its flexibility and ease of use, allowing for rapid response to new scientific ideas. It is scheduled dynamically to match project needs to the available weather. The GBT is also readily reconfigured with new and experimental hardware, adopting the best technology for any scientific pursuit. Facilities of the Green Bank Observatory are also used for other scientific research, for many programs in education and public outreach, and for training students and teachers. 

Quick Facts about the GBT:
The GBT is running observations roughly 6,500 hours each year, more than any other observatory
For each hour of time available for science on the GBT, roughly 3-4 hours are requested
More than 600 individual scientists and students proposed to use the GBT within the past year
More than $25,000,000 has been invested in the GBT in the past five years by colleges, universities, the NSF, and the state of West Virginia
The surface of the GBT is perfectly smooth to a noise level of 260 microns (5 human hairs)
The pointing accuracy of the GBT is 2 arc seconds, able to resolve a quarter at 3 miles
The GBT weighs almost 17 million pounds and stands over 485 feet above ground levelThe GBT’s collecting area is 2.34 acres and its diameter is 300 feet
The GBT operates 24 hours/day, 362 days/year
The operational funding provided by the NSF is approximately 0.1% of the NSF astronomy budget 

Coordinates:  Longitude: 79°50’23.406″ West (NAD83); Latitude: 38°25’59.236″ North (NAD83); Track Elevation: 807.43 m (NAVD88)
Optics:  110 m x 100 m unblocked section of a 208 m parent paraboloid; Offaxis feed arm
Telescope Diameter: 100 m (effective)
Available Foci: Prime and Gregorian; f/D (prime) = 0.29 (referred to 208 m parent parabola); f/D (prime) = 0.6 (referred to 100 m effective parabola); f/D (Gregorian) = 1.9 (referred to 100 m effective aperture)
Receiver mounts: Prime: Retractable boom with Focus-Rotation Mount; Gregorian: Rotating turret with 8 receiver bays
Subreflector: 8-m reflector with Stewart Platform (6 degrees of freedom)
Main Reflector: 2004 actuated panels (2209 actuators); Average intra-panel RMS 68 μm
FWHM Beamwidth: Gregorian Feed: ~ 12.60/fGHz arcmin; Prime Focus: ~ 13.01/fGHz arcmin (see Section 4.1.1 of the Observer’s Handbook)
Elevation Limits: Lower limit: 5 degrees; Upper limit: ~ 90 degrees
Declination Range: Lower limit: ~−46 degrees; Upper limit: 90 degrees
Slew Rates: Azimuth: 35.2 degrees/min; Elevation: 17.6 degrees/min
Surface RMS: Passive surface: 450μm at 45° elevation, worse elsewhere; 
Active surface: ~250μm, under benign night-time conditions
Pointing accuracy: 1σ values from 2-D data; 5″ blind; 2.2″ offset

image of Green Bank Telescope with sunburst