Arecibo: Rise and fall of once world’s largest telescope

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Arecibo
Large radio telescope dish in Arecibo national observatory. Photo : Dreamstime

Mankind has always been curious to look into space and see the unseen. To this effort, scientists have built telescopes, sent missions in space. The story of the Arecibo telescope at the National Astronomy and Ionosphere Center (formerly known as the Arecibo Ionosphere Observatory) had a little different motivation though. The United States Department of Defense wanted to test its missile defense program. Particularly, they were interested to detect the Soviet missiles that travel through the Ionosphere.

This telescope was built to primarily study the Ionosphere. But it served as a general-purpose radio telescope to look into the space for new galaxies and what not! Arecibo telescope was the world’s largest single-aperture telescope until 2016 and was operational in 1963. On December 1, 2020 the telescope fell down due to cable ruptures and was destroyed.

The Arecibo telescope and its contribution

The telescope was built with a large inverted spherical dome shape signal collecting dish and constructed inside a natural sinkhole. The dish has a diameter of 305 meters with a radius of curvature of 265 meters. It was equipped with a cable-mount steerable receiver and several radar transmitters mounted 150 meters above the dish for signal emission. Originally, it was thought that the radars might be able to spot missile trails left in the Ionosphere. But with the limited knowledge of the Ionosphere at that time, the large dish was only meant to serve as a giant radar for probing it.

The telescope had also been used for radar astronomy and radio astronomy. It was used in the Search for Extraterrestrial Intelligence (SETI) program of the US government. Arecibo telescope was also used by NASA to detect Near-Earth objects. To this end, it served the community by finding the first binary pulsar (a pair of neutron stars that emits regular radio bursts) in 1974. You will be astonished to know that from the study of the tracks of the pulsar, the Arecibo telescope produced the first indirect evidence for Gravitational Wave as early as 1978.

The radar, equipped with this telescope mapped 25% of Venus’s cloud-shrouded surface in 1980. It also revealed an asteroid with a peanut shape that stands for a contact binary system held together by weak gravity. In 1991, the possibility of deposition of ice was discovered near Mercury’s north pole by this telescope. Until its collapse in 2020, the Arecibo telescope made a significant contribution in the field of Space Science and Astronomy.

Crash of the telescope

This telescope has its rise and even associated its name with a James Bond movie (GoldenEye, 1995). Hurricane Maria in 2017 did some damage to it. But it was in 2020, that the final blow came in. Astronomer Sravani Vaddi was studying a distant galaxy named NGC 7469 with the telescope for an hour slot in the early morning (2 a.m) of August 10, 2020. Towards the end of her slot, around 2.45 a.m. an 8 cm thick cable, amongst the 18 others that hold the 900-ton instrument platform, had pulled out.

The cable fell slicing the dish. A second support cable snapped on November 3. The authority measured the situation and stated that the repair attempt was very dangerous. Finally, it was decided to dismantle the telescope. But on December 1, a couple of more support cables snapped and the platform came crashing down into the dish. The loss dismayed scientists worldwide.

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