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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Arecibo Telescope | 1/6 | https://en.wikipedia.org/wiki/Arecibo_Telescope | reference | science, encyclopedia | 2026-05-05T13:15:38.928164+00:00 | kb-cron |
The Arecibo Telescope was a 305 m (1,000 ft) spherical reflector radio telescope built into a natural sinkhole at the Arecibo Observatory located near Arecibo, Puerto Rico. A cable-mounted, steerable receiver and several radar transmitters for emitting signals were mounted 150 m (492 ft) above the dish. Completed in November 1963, the Arecibo Telescope was the world's largest single-aperture telescope for 53 years, until it was surpassed in July 2016 by the Five-hundred-meter Aperture Spherical Telescope (FAST) in Guizhou, China. Decommissioning the Arecibo Telescope was announced in November 2020, and the telescope collapsed in December 2020. The Arecibo Telescope was primarily used for research in radio astronomy, atmospheric science, and radar astronomy, as well as for programs that search for extraterrestrial intelligence (SETI). Scientists wanting to use the observatory submitted proposals that were evaluated by independent scientific referees. NASA also used the telescope for near-Earth object detection programs. The observatory, funded primarily by the National Science Foundation (NSF) with partial support from NASA, was managed by Cornell University from its completion in 1963 until 2011, after which it was transferred to a partnership led by SRI International. In 2018, a consortium led by the University of Central Florida assumed operation of the facility. The telescope's unique and futuristic design led to several appearances in film, gaming and television productions, such as for the climactic fight scene in the James Bond film GoldenEye (1995). It is one of the 116 pictures included in the Voyager Golden Record. It has been listed on the US National Register of Historic Places since 2008. The telescope was named an IEEE Milestone in 2001. The NSF reduced its funding commitment to the observatory from 2006, leading academics to push for additional funding support to continue its programs. The telescope was damaged by Hurricane Maria in 2017 and was affected by earthquakes in 2019 and 2020. Two cable breaks, one in August 2020 and a second in November 2020, threatened the structural integrity of the support structure for the suspended platform and damaged the dish. Due to uncertainty over the remaining strength of the other cables supporting the suspended structure, and the risk of collapse owing to further failures making repairs dangerous, the NSF announced on November 19, 2020, that the telescope would be decommissioned and dismantled, with the LIDAR facility remaining operational. Before it could be decommissioned, several of the remaining support cables suffered a critical failure and the support structure, antenna, and dome assembly all fell into the dish at 7:55 a.m. local time on December 1, 2020, destroying the telescope. The NSF decided in October 2022 that it would not rebuild the telescope or build a similar observatory at the site.
== General information ==
The telescope's main collecting dish had the shape of a spherical cap 305 metres (1,000 ft) in diameter with an 265-metre (870 ft) radius of curvature, and was constructed inside a karst sinkhole. The dish surface was made of 38,778 perforated aluminum panels, each about 1 by 2 metres (3 by 7 ft), supported by a mesh of steel cables. The ground beneath supported shade-tolerant vegetation. The telescope had three radar transmitters, with effective isotropic radiated powers (EIRPs) of 22 TW (continuous) at 2380 MHz, 3.2 TW (pulse peak) at 430 MHz, and 200 MW at 47 MHz, as well as an ionospheric modification facility operating at 5.1 and 8.175 MHz. The dish remained stationary, while receivers and transmitters were moved to the proper focal point of the telescope to aim at the desired target. As a spherical mirror, the reflector's focus was along a line rather than at one point. As a result, complex line feeds were implemented to carry out observations, with each line feed covering a narrow frequency band measuring 10–45 MHz. A limited number of line feeds could be used at any one time, limiting the telescope's flexibility. The receiver was on an 820-tonne (900-short-ton) platform suspended 150 m (492 ft) above the dish by 18 main cables running from three reinforced concrete towers (six cables per tower), one 111 m (365 ft) high and the other two 81 m (265 ft) high, placing their tops at the same elevation. Each main cable was a 8 cm (3.1 in) diameter bundle containing 160 wires, with the bundle painted over and dry air continuously blown through to prevent corrosion due to the humid tropic climate. The platform had a rotating, bow-shaped track 93 m (305 ft) long, called the azimuth arm, carrying the receiving antennas and secondary and tertiary reflectors. This allowed the telescope to observe any region of the sky in a forty-degree cone of visibility about the local zenith (between −1 and 38 degrees of declination). Puerto Rico's location near the Northern Tropic allowed the Arecibo telescope to view the planets in the Solar System over the northern half of their orbit. The round trip light time to objects beyond Saturn is longer than the 2.6-hour time that the telescope could track a celestial position, preventing radar observations of more distant objects.
== History ==
=== Design and construction ===