Green Bank radio telescope, National Radio Astronomy Observatory (NRAO), West Virginia, USA. Also called the Robert C. Byrd Green Bank Telescope or GBT, this is the world's largest fully-steerable radio telescope. It can be manoeuvred to view any part of the sky above 5 degrees elevation. It is mounted on a track mechanism, 64 metres in diameter. The dish, 100 by 110 metres across the surface, is parabolic in shape. The receiver is suspended above the dish at the focus of the parabola to detect incoming radio waves.