Arecibo Observatory

A radio astronomy observatory in Puerto Rico, best known for its 305-meter radio telescope, which collapsed in 2020.

Arecibo radio telescope: The 305-meter fixed spherical radio dish at Arecibo Observatory, used for astronomy, planetary radar, and atmospheric research. Its enormous collecting area made the observatory’s most famous measurements possible.
Pulsar: A rotating neutron star that emits beams of radiation observed as regular pulses. Arecibo observations helped establish the nature of the first binary pulsar.
William E. Gordon: A physicist who proposed and led the development of the Arecibo radio telescope. His ionospheric research inspired the observatory’s original design.
National Science Foundation: A U.S. federal agency that supports fundamental research and education across science and engineering. The agency funded the observatory and oversaw decisions preceding the collapse.
Gregorian reflector: A secondary-reflector system that redirects radio waves to a receiver, improving focus and usable frequency range. A 1997 upgrade added this system above Arecibo’s dish.
PSR B1913+16: A binary pulsar discovered in 1974 whose orbit provides evidence for gravitational-wave energy loss. Arecibo data enabled the measurements that tested general relativity in this system.
Cornell University: A private research university in Ithaca, New York, founded in 1865. Cornell operated Arecibo Observatory for decades after its 1963 opening.
Arecibo Observatory Visitor Center: A public education center at Arecibo Observatory, opened in 1997 and later named for Ángel Ramos. The visitor center remains part of the site’s educational legacy beyond the telescope.
Radar astronomy: The study of Solar System objects by transmitting radio waves and analyzing their echoes. Arecibo could transmit powerful radar signals as well as receive distant radio emissions.
Mercury (planet): The smallest planet in the Solar System and the closest to the Sun. Arecibo radar observations helped determine Mercury’s rotation period.

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