Observatory of Green Bank

The observatory of Green Bank is known primarily to lodge the Green Bank Telescope (GBT) which is largest directional Radiotélescope of the world. Its equipment belongs to the network of the National Radio operator Astronomy Observatory (NRAO) and is located at Green Bank in Virginia-Western with the the United States. The observatory is installed in the center of the American zone of radio silence (United States National Radio operator Calm Zone), a rectangle of more than: 33000 km ² where are banished or severely limited the radio transmissions.

The GBT

The construction of the telescope was decided after the collapse of its predecessor, a parabola of 90 m, the November 15th 1988, which had with the loss of a paramount Gousset in the assembly of the beams out of box. Built between 1991 and 2002, it received its first light on August 22nd 2000. It is more precisely named telescope Robert C. Byrd de Green Bank in homage to the senator Robert Byrd.

The collecting surface of: 7854 m ² measurement 100 by 110 meters and is made up of: 2004 elementary panels adjusted actively by: 2209 independent actuators. These panels in Aluminum are worked with a precision of ~75 µm RMS . The mechanisms of adjustment make it possible to correct the mechanical deformations due to gravity during the changes of orientation of the telescope. Without this " surface active" , it would be impossible with the GBT to precisely work in the frequencies higher than 4 GHz; with, it can be used theoretically until 100 GHz.

Its structure is unusual in the direction where the mirror does not have a symmetrical form but is a section of Paraboloïde which does not include the axis of the hearth. The excentric position of the receivers to the hearths makes it possible their support not to be in the observation field, thus avoiding the problems of reflection and parasitic Diffraction.

With the primary education hearth of the antenna is a retractable horn of food, and behind him the reflecting secondary is held of 8 m thus constituting a Gregorian mounting. With the secondary focus (Gregorian) is eight horns of highher degree of accuracy, assembled on a rotary turret. The exploited frequencies go from 290 MHz with 49,8 GHz. Since September 2006, an instrument with 90 GHz named MUSTANG ( Multiplexed SQUID/TES Array for Ninety Gigahertz ) is tested: it is more the high frequency observed to date on the GBT and the first imagor with pixel.

The telescope is equipped with a laser system pointing on the panels of the reflectors primary education in order to measure and to precisely compensate for the distortions due to gravity, the wind, dilation etc…

Other telescopes

The telescope of 43 m is the largest radio telescope on equatorial Monture of the world. It is primarily used to study turbulences of the terrestrial Ionosphère in bistatic configuration with the Observatoire of Millstone Hill of the MIT.

GBSRBS ( Green Bank Solar Radio operator Burst Spectrometer ) is dedicated to the observation of the solar radio bursts, which its situation in zone of radio silence allows. Incidentally, NASA uses it for the follow-up of the satellites of interferometry at very long space base.

GBI is a whole of three antennas of 26 m (85 foot S), named 85-1, 85-2 and 85-3, being able to constitute a interferometer. Telescope 85-1 also named telescope Tatel , built in 1958, was one of the pioneers of radio operator astronomy with the NRAO. Telescope 85-3, going back to 1989, is dedicated to the continuous observation of the Pulsar S and follows 35 per day from there.

The telescope of 20 m built in 1994, belonged to the network of Geodesy VLBI of NASA.

See too

Internal bonds

List of the astronomical observatories

References

External bonds

Official site of the GBT with the NRAO
air showing the GBT in construction

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