Arecibo Observatory, Astronomical observatory in Puerto Rico

Arecibo Observatory was a radio telescope facility in Puerto Rico that sat within a natural limestone depression and once conducted measurements through a 305-meter metal mesh. The facility included a platform above the dish from which signal-receiving equipment was suspended.

The facility began operations in 1963 and developed over decades into a leading site for atmospheric and planetary research. A change in management occurred in 2011 when other institutions took over operational leadership.

The site's name comes from Arecibo, the municipality whose Barrio Esperanza holds the observatory, about 15 km south of the coastal town. The visitor center drew roughly 100,000 people a year before the collapse. In 2023 the NSF chose a university consortium to run Arecibo C3, an education center for science education and computational skills.

The site lies about 15 km south of the port city of Arecibo, in Barrio Esperanza. The telescope collapsed on 1 December 2020 and the NSF decided in 2022 not to rebuild it; the visitor center stayed open after the collapse, and a consortium of universities is setting up the Arecibo C3 education center there. Check current opening arrangements before travelling.

The facility served as a filming location for two well-known movies in the 1990s and introduced the telescope to a worldwide audience. Scientists sent a coded message into space from here in 1974 aimed at possible extraterrestrial civilizations.