English: A 100 meter (300 foot) radio telescope built at Green Bank, West Virginia by the US National Radio Astronomy Observatory (NRAO) completed 30 August 1962, which was the world's largest aperture radio telescope at the time. It saw first light 21 September 1962. It was a transit telescope, mounted on a rocker that only allowed steering in a north-south plane, which could not track astronomical objects as the Earth turned but observed them briefly as they passed through it's pattern overhead. During its observing life it studied supernova remnants and movement of gas in galaxies, accumulating data that led to the discovery of dark matter. It collapsed 9:43pm on 3 November 1988 due to a cracked gusset plate. On the site in 2001 the 100 meter Robert C. Byrd Green Bank Telescope was built, the current largest aperture steerable radio telescope