Green Bank Telescope — radio telescope
NRAO/AUI/NSF · CC BY 4.0

Green Bank Telescope

  • 2 min read
  • 38.433° N 79.840° W

Interesting facts

  • At 148 metres tall the GBT rises about 60 per cent higher than the Statue of Liberty, pedestal included.
  • The whole structure weighs some 7,600 tonnes, yet it turns smoothly on a circular rail track 64 metres across.
  • Its dish is made of 2,004 aluminium panels moved by 2,209 actuators, holding the surface accurate to better than 50 micrometres.
  • The collecting surface covers about 2.3 acres, or more than 9,000 square metres.
  • Construction began on 19 December 1990, and regular science operations started in 2001 after a decade of building.
  • The telescope is used for astronomy about 6,500 of the 8,760 hours in a year, an unusually high share for any observatory.
  • It can reach about 85 per cent of the sky above Green Bank and observes from 0.1 to 116 gigahertz, wavelengths from 3 metres down to under 3 millimetres.
  • In 2019 the GBT measured PSR J0740+6620, at the time the most massive neutron star ever found, packing over twice the Sun's mass into a city-sized ball.
  • In 2002, soon after it began work, astronomers used it to discover three new millisecond pulsars in the globular star cluster Messier 62.

Why it is worth it

The Robert C. Byrd Green Bank Telescope, known simply as the GBT, is the largest fully steerable radio telescope in the world. Its reflecting surface measures 100 by 110 metres, and it can point to almost any part of the sky above the horizon. It stands in a quiet valley in Pocahontas County, West Virginia, inside the National Radio Quiet Zone, a region of about 13,000 square miles created by the federal government in 1958 where radio transmissions are tightly restricted to protect the observatory's receivers.

The GBT was born from an accident. On the night of 15 November 1988, the observatory's 300-foot telescope, then the largest instrument on the site, suddenly collapsed after a key steel support failed. Congress funded a replacement, construction began in 1990, and the new telescope saw first light in August 2000. Instead of a conventional design with a receiver platform held in front of the dish on legs, the GBT uses an off-axis reflector: the receiver arm rises from one side, so no struts block incoming radio waves. The surface consists of more than two thousand panels, each mounted on motorised actuators that constantly adjust its shape to correct for gravity and heat.

The telescope works from long radio waves to millimetre wavelengths. It has discovered many pulsars, including the fastest and some of the heaviest known, it is a core instrument of the NANOGrav collaboration, which timed pulsars to find evidence of a background of low-frequency gravitational waves, and it maps molecules and gas across the galaxy. It was the flagship of the National Radio Astronomy Observatory until 2016, when Green Bank became an independent observatory funded by the National Science Foundation.

Getting there

Green Bank is about 74 km from Staunton, Virginia, the nearest city, and the closest airport is Greenbrier Valley Airport (LWB), about 81 km away; the final approach is by winding mountain roads. The Green Bank Science Center is open to visitors with a free exhibit hall, and guided tours of the site, including bus tours near the telescopes, start there. Because of the radio-quiet zone, mobile phones and digital cameras cannot be used near the telescopes, and phones should be switched off on the site's walking and cycling trails. Expect little or no mobile coverage in the whole valley.

On these lists

The Most Beautiful Places in the United States 228The Most Remarkable Radio Telescopes 6The Greatest Modern Engineering Wonders in the United States 7The Greatest Engineering Wonders in the United States 26The Greatest Modern Engineering Wonders 26The Greatest Engineering Wonders 271

From the encyclopaedia

The Robert C. Byrd Green Bank Telescope (GBT) in Green Bank, West Virginia, US is the world's largest fully steerable radio telescope, surpassing the Effelsberg 100-m Radio Telescope in Germany. The Green Bank site was part of the National Radio Astronomy Observatory (NRAO) until September 30, 2016. Since October 1, 2016, the telescope has been operated by the independent Green Bank Observatory. The telescope's name honors the late Senator Robert C. Byrd who represented West Virginia and who pushed the funding of the telescope through Congress.

Wikipedia · CC BY-SA 4.0

38.43312, -79.83983per Wikidata