Puerto Rico // The north coast and karst country //

Observatorio de Arecibo

The world’s largest radar and radio telescope, the Observatorio de Arecibo (t787/878-2612, whttp://www.naic.edu) is an immense 300-metre concave dish surrounded by jungle-drenched limestone peaks. Scientists come here to gaze into the deepest corners of the galaxy and the giant installation has an appropriately serene, isolated feel.

The visitor centre contains an illuminating series of exhibits that explain the pioneering research that takes place here, with sections on the Earth and our solar system, stars and galaxies and tools and technology. Short videos look at the Big Bang Theory, the birth and death of stars and finally the Solar System, a mind-blowing imaginary journey that starts with the telescopic protons of a human being and ends at the outer limits of the universe.

Step outside onto the viewing deck and the vast size of the reflector dish is brought home. Below, 38,778 aluminium panels hang just over the jungle canopy, supported by a network of steel cables. Suspended 137m above the dish is a monitoring station and a series of precarious-looking walkways, held up by eighteen cables strung from three reinforced concrete towers (the tallest is 110m). The whole site is surrounded by a typical karst landscape, thick with verdant outcrops of limestone and enveloped with an almost eerie calm.

The telescope was conceived by Dr William E. Gordon at Cornell University and constructed between 1960 and 1963, making it one of the oldest still in use. The location was chosen principally because of its proximity to the equator (which provides the clearest views of the night sky) and the surrounding limestone formations, which provided a natural shell in which to build it. Unlike optical telescopes, it works by collecting radiation in the radio region of the electromagnetic spectrum – the dish concentrates the radio waves so that scientists can detect all sorts of objects in space, from pulsars and quasars to black holes and, one day perhaps, signs of extraterrestrial life. Cornell University still operates the telescope, under contract with the National Science Foundation.