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GBT Basics

When our 300-foot radio telescope suddenly collapsed on the night of November 15th, 1988, the United States lost its largest moveable single dish telescope. Then West Virginia Senator Robert C. Byrd began rallying for a replacement telescope, and only two years after the collapse, the National Science Foundation approved a new telescope in Green Bank, what would become the largest fully steerable telescope in the world – the Robert C. Byrd Green Bank Telescope.

The GBT began observations in Green Bank, West Virginia in 2000 and is a wonder for many reasons, not the least of which is its enormous size. An impressive parabolic dish covering 2.3 acres, the GBT has the largest collecting area of any fully-steerable telescope in the world.

From the base to the top of its huge feed arm, the GBT stands 485 feet tall. Its 100-meter by 110-meter dish required 7,652 beams to support it on top of a nearly hemispherical tilting gear. A gigantic yoke cradles that gear above a base of concrete sunk 25 feet down to solid Appalachian bedrock.

Over 17 million pounds of telescope glide around its 360-degree concrete track, thanks to four four-wheeled trucks, making the GBT the largest moving object on land. Its remarkable agility allows it to see 85% of the skies surrounding the Earth over the course of a year.


Its 200-foot feed arm is a two-towered trusswork sticking out of the side of the dish and ending in a secondary mirror perched 60 feet above the dish. The secondary aims the dish’s focused radio waves into one of eight receivers hanging in a rotating turret. On the fly, a new receiver can be spun into the beam to change the frequency being recorded. A ninth receiver can swing out on a boom arm in place of the secondary, giving astronomers a huge range of science they can pursue with one telescope.

Scientists from around the world use the GBT to observe the skies for 6500 hours every year. The GBT’s gigantic, unobstructed dish provides scientists with sensitive eyes on the faintest radio objects in the Universe, such as gas clouds between the galaxies and the hidden chemistry between the stars. The hyperaccurate surface gives scientists the ability to measure very tricky values for pulsar timings and interpret values for dark matter and energy.

In 2016, the Green Bank Observatory took over operations for the GBT.

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