For 53 years an 820-ton platform hung 150 meters above a 305-meter dish set into a Puerto Rican sinkhole. On December 1, 2020, the cables gave way and it crashed through the reflector below. This episode traces the full life of the Arecibo Observatory, beginning with Project Defender and the Cold War need to distinguish incoming nuclear warheads from decoys by studying their ionospheric wakes. We follow Cornell physicist William Gordon’s search for a natural bowl in the limestone karst, and the Doundoulakis brothers’ suspended azimuth arm design that replaced a fixed central tower.

We then walk through the science: bouncing radar off Mercury in 1964 to correct its rotation period to 59 days, confirming neutron stars via the Crab Pulsar in 1968, the Hulse-Taylor binary pulsar that tested general relativity and earned a Nobel Prize, Aleksander Wolszczan’s discovery of the first exoplanets around a pulsar, and the 1974 Arecibo message aimed at Messier 13. Finally we examine the funding decline, Hurricane Maria, the failed 1980s zinc socket, the August 2020 cable slip, and the National Academies report on lost institutional knowledge.

• How a sinkhole and a 40-degree cone of visibility near the equator gave a fixed dish a sweeping view of the planetary plane
• Active radar versus passive listening, from mapping Venus through its clouds to imaging asteroids
• The 1,679-bit Arecibo message, its 73-by-23 grid, and the ongoing debate over announcing our location
• Why moisture in the cable sheaths, disabled dry-air blowers, and budget cuts led to the collapse
• What survived: three petabytes of recovered data and a site being converted into a STEM education center