" " A starry sky above the Arecibo Observatory in Puerto Rico, taken on Aug. 4, 2020. University of Central Florida For 57 years, the Arecibo Observatory, a radio/radar telescope facility located about 12 miles (19 kilometers) south of the city of Arecibo in Puerto Rico, was one of astronomy's great treasures. Until recently, Arecibo had the biggest radio telescope in the world, and its ability to detect distant signals made it one of the world's most powerful tools for studying both planets and moons in our own solar system and mysterious objects in distant regions of the universe. Over the years, scientists used it to determine Mercury's rotation rate and map the surface of Venus, to discover the first binary pulsar and the first known exoplanet. Arecibo's researchers also made important findings about the properties and orbits of asteroids that are potentially hazardous to Earth.