The cable car looks not on white slopes and prancing skiers but on the tropical green and brown of Puerto Rican forests. At the top terminus you can look straight down a distance equal to the height of the Washington monument. You look into the center of the world's largest dish—18 acres of wire mesh on a carefully positioned spherical network of supporting cables. You walk around on a 500‐ton assembly that supports two carriage houses, a workshop, cables, waveguides and motors to turn and slide its various parts. Below extend the horns, snouts and Yagi antennas that can transmit and receive radio frequencies between 20 and 600 megahertz. A few miles south of the northern coast of Puerto Rico, this is the radar and radio telescope of the Arecibo Ionospheric Observatory. It was dedicated in 1963 (PHYSICS TODAY, January 1964, page 66).

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