The Robert C. Byrd Green Bank Telescope (GBT) is the world’s largest fully steerable radio telescope. It is located at the U.S. National Radio Astronomy Observatory’s Green Bank site in Pocahontas County, West Virginia. Another large radio telescope at Green Bank, which was a slightly smaller telescope than the current one, collapsed in 1988 after twenty-five years of operation.

The current GBT weighs more than 16 million pounds (7,500 tons) and has a collecting area nearly twice the size of a football field; it is slightly off-axis, and is not exactly round, at 110 meters long and 100 meters across. The focal point is at the end of an arm that reaches over the dish from one side. The telescope is mounted on a track 210 feet (64 meters) in diameter that is level to within a few thousandths of an inch. The track allows the telescope to view the entire sky in any direction. Furthermore, each of the 2,004 panels that make up its surface are mounted on motor-driven pistons. This way, the shape of the surface can be carefully adjusted to make very precise observations.