Green Bank radio telescope. Dish antenna of the 43-metre (140-feet) radio telescope at the Green Bank observatory in West Virginia, USA. The surface of the parabolic antenna is covered with a precise reflecting surface of aluminium foil which allows observations at wavelengths of 2 centimetres and above. It is used for observing narrow spectral lines such as those emitted by ionised hydrogen and helium. It has been used for interferometric observations with other American and European telescopes to produce highly-detailed images. This telescope commenced operation in 1965, and in 1997 is operated by the National Radio Astronomy Observatory (NRAO).