The Arecibo Observatory is on the island of Puerto Rico. The US National Science Foundation constructed the observatory in the early 1960s. They built the Arecibo Telescope’s 305-metre wide reflector dish into a natural depression in the ground. For decades, it was the largest single-dish radio telescope in the world. The observatory closed in 2020.
The Arecibo Observatory conducted a whole range of astronomical observations. It measured the rotation rates of planets and discovered pulsars. It even searched for signs of extra-terrestrial life as part of the SETI programme. The telescope also featured in the films Contact and GoldenEye.
Some radio telescopes spin to observe specific locations in the sky. The Arecibo dish was too massive to move so scientists and engineers designed a moveable detector. This let the telescope receive signals from nearly a quarter of the visible sky. As the Earth rotated, the telescope observed a large region of the sky across the day and night. Remember, radio telescopes can observe during the daytime because they do not collect normal visible light.
Scientists used electric motors to move the detector with millimetre precision. Eighteen cables held the 900 tonne detector platform 150 metres above the base of the dish. Breaks in two of these cables led to the closure of the telescope in 2020.