How it began
The Arecibo Observatory opened in November 1963 in northern Puerto Rico. William E. Gordon of Cornell University, later called the father of the observatory, led its development and construction, with funding from the US Advanced Research Projects Agency. The site was chosen because a natural sinkhole in the karst landscape provided a ready concave surface for the dish, and because Puerto Rico was a US territory close to the equator. Gordon recalled that when engineers first asked how long the structure should last, the team settled on ten years.
How it works
The telescope was a fixed reflector 305 meters across, laid into the sinkhole. Its receiver hung on a platform suspended from cables more than 400 feet above the dish, reached by a cable car and a catwalk.
The original surface was wire mesh, which workers crossed on boards like snowshoes. In 1974 it was resurfaced with aluminum panels. The observatory could transmit as well as receive, which made it a radar instrument for studying planets, asteroids and the upper atmosphere.
What changed first
Among the telescope's earliest results was a corrected rotation period for Mercury of 59 days, about a month shorter than previously thought. After pulsars were discovered in 1967, Arecibo proved especially well suited to studying them. In 1974 Russell Hulse and Joseph Taylor used it to find the first pulsar in a binary system. Their observations gave the first indirect confirmation of gravitational waves and earned the 1993 Nobel Prize in Physics.
What lasted
Over 57 years the telescope was used for radio astronomy, ionospheric and atmospheric research, radar monitoring of near-Earth objects and the search for extraterrestrial communication. Discoveries made with it include the first exoplanet and the first repeating fast radio burst. It was the largest single-aperture telescope in the world until 2016. As one University of Puerto Rico professor put it after the collapse, "The world without the observatory loses, but Puerto Rico loses even more."
Where it stands today
In 2020 several support cables failed and damaged the dish. The National Science Foundation announced in November 2020 that the telescope would be decommissioned, and on December 1 the receiver platform fell into the dish. No one was hurt. The NSF decided not to rebuild the telescope and chose instead to repurpose the site as a center for STEM education. The structure had been weakened by hurricane damage and strained by funding cuts in its last years.
