Arecibo

Radio telescopes, like this one (the world's largest) at Arecibo, Puerto Rico, allow astronomers to analyse a broad range of low-frequency electromagnetic waves – visible light is only a small part of the electromagnetic spectrum. Pulsars and quasars were first discovered by radio telescopes.

Town in northwest Puerto Rico; population (2001 est) 49,800. It is located on the Atlantic Ocean at the mouth of the Arecibo River, 77 km/48 mi to the west of San Juan. This colonial centre was originally settled in the mid-16th century. A port with some light manufacturing facilities and the site of a college of the University of Puerto Rico, it is also a trade, processing, and distribution hub for an agricultural region producing sugar cane, coffee, fruit, and tobacco. The rum, pharmaceutical, plastics, machinery, and clothing industries are also important. The Cueva del Indio caves and the Río Camuy Cave Park are nearby, and 19 km/12 mi to the south is Cornell University's Arecibo Observatory, the site of the world's largest single-dish radio telescope.