ARECIBO OBSERVATORY

astronomical observatory located 16 km (10 miles) south of the town of Arecibo in Puerto Rico; it is the site of the world's largest single-unit radio telescope. This instrument, built in the early 1960s, employs a 300-metre (1,000-foot) spherical reflector consisting of perforated aluminum panels that focus incoming radio waves on movable antenna structures positioned about 168 m (550 feet) above the reflector surface. The antenna structures can be moved in any direction, making it possible to track a celestial object in different regions of the sky. The observatory also has an auxiliary 30-metre telescope that serves as a radio interferometer and a high-power transmitting facility used to study the Earth's atmosphere. The Arecibo Observatory has produced detailed radar maps of the surface of Venus and precise information about that planet's rotation. The observatory also has made such contributions to radio astronomy as the detection of neutron star matter in pulsars.