Green Bank Telescope

Infobox Telescope
name = Green Bank Telescope


organization = NRAO
location = Green Bank, West Virginia, USA
coords = coord|38|25|58.23|N|79|50|21.88|W|display=inline,title
wavelength = radio
built = 1991-2002
first_light = August 22, 2000
style = Parabolic off-axis reflector, Gregorian optics
diameter = 100m
area = 7,854m²
focal_length = 60 m
mounting = wheel and track mount
website = nowrap| [http://www.gb.nrao.edu/GBT/GBT.shtml 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. [ [http://www.gb.nrao.edu/fgdocs/300ft/300ft.html NRAO 300 foot Telescope Home Page ] ]

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.

Description

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 efficient. [cite web |url=http://www.gb.nrao.edu/gbtprops/man/GBTpg.pdf |title=The Proposer’s Guide for the Green Bank Telescope |author=Toney Minter |year=2007 |month=May |accessdate=2007-07-14 |publisher=NRAO |format=PDF]

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.

Discoveries

In 2002, astronomers detected three new millisecond pulsars in the globular cluster Messier 62. [ [http://www.nrao.edu/pr/2002/gbtpulsars/ Newly Commissioned Green Bank Telescope Bags New Pulsars] , NRAO, 2002-01-04]

In 2006, several discoveries were announced, including a large coil-shaped magnetic field in the Orion molecular cloud, [ [http://www.accessmylibrary.com/coms2/summary_0286-12363238_ITM Green Bank Telescope scores big finds in space: Fastest pulsar Slinky magnetics superbubble of hydrogen ID] , The Charleston Gazette, 2006-01-17] and a large hydrogen gas superbubble 23,000 light years away, named the Ophiuchus Superbubble. [ [http://arxiv.org/abs/astro-ph/0610894v1 The Ophiuchus Superbubble: A Gigantic Eruption from the Inner Disk of the Milky Way] , ArXiv] cite news | title=Huge 'Superbubble' of Gas Blowing Out of Milky Way | date=2006-01-13 | publisher= | url =http://www.physorg.com/news9882.html | work =PhysOrg.com | accessdate = 2008-07-04 |]

Image Gallery

ee also

* List of radio telescopes

References

External links

* [http://www.gb.nrao.edu/GBT/GBT.shtml Official site]
* [http://terraserver-usa.com/usgsentry.aspx?T=1&S=10&Z=17&X=3006&Y=21272&W=3&qs=%7cgreen+bank%7cwv%7c Aerial photo that happened to catch telescope while it was under construction]
* [http://www.davidmetraux.com/westva.html Collection of West Virginia photos including Green Bank] from davidmetraux.com