Arecibo Observatory, large, stationary radio telescope, with attendant facilities, that is part of Cornell University's National Astronomy and Ionosphere Center. The telescope, located 15 km (9 mi) south of Arecibo on the northern coast of Puerto Rico, is a bowl-shaped dish set into a natural hollow. The dish, 305 m (1000 ft) wide, consists of nearly 40,000 individual reflecting panels attached to a network of steel cables. The panels focus incoming radio waves from outer space onto a detecting platform suspended above the dish. The platform can be adjusted to enable the telescope to observe the sky from 43° North to 6° South. It can also transmit signals and has been used for radar-reflection studies of the moon. A smaller radio telescope, used along with the main dish for interferometric studies, is located north of the observatory; it is 30 m (98 ft) wide.
The observatory was completed by Cornell University in 1963 and is operated under contract with the National Science Foundation. The telescope is used for studying the earth's upper and middle atmospheres as well as sources of radio waves in deep space (see Radio Astronomy). It has also been used to search for radio signals that would indicate the existence of extraterrestrial life (see Exobiology).
In 1997, engineers and scientists completed a five-year project to upgrade the Arecibo observatory. They installed two new reflecting panels on the telescope, making it four times more sensitive to deep space radio signals than before the upgrade. Radio astronomers can use this increased sensitivity for more extensive observations and studies. However, even with the improved system, radio astronomers at Arecibo (and at other radio astronomy facilities around the world) must deal with increasing radio frequency pollution (radio signals coming from human-made sources) . Radio astronomers monitor frequencies on the electromagnetic spectrum (EMS) that are very close to the frequencies used by cellular telephones, a major cause of the frequency pollution. As of 1998, a solution to this issue was still under development. Radar Astronomy.