Arecibo Observatory, Puerto Rico, US Territories

Arecibo Observatory is a unique radio telescope, officially known as the National Astronomy and Ionosphere Center, operated by a consortium of universities, research organizations, and the National Science Foundation, and located in the US territory of Puerto Rico. It is a 1000 foot wide dish, with 38,700 perforated aluminum panels set in a suspended mesh of wires, a few feet above the ground over an old karst sinkhole. It was built in 1963, designed by William E Gordon, a scientist from Cornell, as an ionospheric research facility, associated with scientific and military interests, and was supported by defense department’s ARPA. It has also been used by SETI, to search for extraterrestrial intelligence. It was operated chiefly by Cornell University until 2011, and until a bigger dish was built in China in 2016, this was the largest single-aperture telescope in the world.