Arecibo Observatory, radio-astronomy facility located near Arecibo, Puerto Rico, part of the National Astronomy and Ionosphere Center. Conceived by, designed by, and built under the supervision of William E. Gordon, it was completed in 1963 and is now operated by the Univ. of Central Florida, Ana G. Méndez Univ., and Yang Enterprises under contract with the U.S. National Science Foundation. The principal instrument, the William E. Gordon Telescope, was a fixed antenna of spherical section, 1,000 ft (305 m) in diameter; long the world's largest single-dish radio telescope, it was built into a natural limestone bowl. Although the antenna was too large and heavy to be moved, it could be pointed as much as 20° from the zenith by moving the line feeds to the antenna's focus. As a result of the resurfacing of the antenna, which was completed in 1974, observations were possible up to a frequency of 4,000 MHz. Cable failures, resulting damage, and safety issues led in 2020 to a decision to decommission the radio telescope; the receiver platform subsequently collapsed. A 100-ft (30-m) satellite antenna was used in conjunction with the large antenna for interferometer observations. There also is a wide range of instrumentation for measuring ionospheric conditions. Principal research programs have included studies of radio emissions from many types of objects, especially the cores of supernovas called pulsars; radar studies of comets and asteroids; and ionospheric studies.
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