The observatory's 305 m radio telescope is the largest single-aperture telescope (cf. multiple aperture telescope) ever constructed. It carries out three major areas of research: radio astronomy, aeronomy (using both the 305 m telescope and the observatory's lidar facility), and radar astronomy observations of solar system objects. Usage of the telescope is gained by submitting proposals to the observatory, which are evaluated by an independent board of referees.
The telescope is visually distinctive and has been used in the filming of notable motion picture and television productions: as the villain's antenna in the James Bond movie GoldenEye, as itself in the film Contact and in the "X-Files" episode "Little Green Men". The telescope received additional international recognition in 1999 when it began to collect data for the SETI@home project.
It is a spherical reflector (as opposed to a parabolic reflector). This form is due to the method used to aim the telescope: the telescope's dish is fixed in place, and the receiver is repositioned to intercept signals reflected from different directions by the spherical dish surface. A parabolical mirror would induce a varying astigmatism when the receiver is in different positions off the focal point, but the error of a spherical mirror is the same in every direction. The receiver is located on a 900-ton platform which is suspended 150 m (500ft) in the air above the dish by 18 cables running from three reinforced concrete towers, one of which is 110m (365ft) high and the other two of which are 80 m (265 ft) high (the tops of the three towers are at the same elevation). The platform has a 93 m long rotating bow-shaped track called the azimuth arm on which receiving antennas, secondary and tertiary reflectors are mounted. This allows the telescope to observe any region of the sky within a forty degree cone of visibility about the local zenith (between -1 and 38 degrees of declination). Puerto Rico's location near the equator allows Arecibo to view all of the planets in the solar system, though the round trip light time to objects beyond Saturn is longer than the time the telescope can track it, preventing radar observations of more distant objects.
The construction of the Arecibo telescope was initiated by Professor William E. Gordon of Cornell University, who originally intended to use it for the study of Earth's ionosphere. Originally, a fixed parabolic reflector was envisioned, pointing in a fixed direction with a 150m (500ft) tower to hold equipment at the focus. This design would have had a very limited use for other potential areas of research, such as planetary science and radio astronomy, which require the ability to point at different positions in the sky and to track those positions for an extended period as Earth rotates. Ward Low of the Advanced Research Projects Agency (ARPA) pointed out this flaw, and put Gordon in touch with the Air Force Cambridge Research Laboratory (AFCRL) in Boston, Massachusetts where a group headed by Phil Blacksmith was working on spherical reflectors and another group was studying the propagation of radio waves in and through the upper atmosphere. Cornell University proposed the project to ARPA in the summer of 1958 and a contract was signed between the AFCRL and the University in November 1959. Cornell University published a request for proposals (RFP) asking for a design to support a feed moving along a spherical surface above the stationary reflector. The RFP suggested a tripod or a tower in the center to support the feed. George Doundoulakis, director of research for the antenna design company General Bronze Corp in Garden City, N.Y. received the RFP from Cornell and studied it with his brother, Helias Doundoulakis, a civil engineer.
The two brothers thought of a more efficient way to suspend the feed, and finally designed the cable suspension system that was used in final construction. The U.S. Patent office granted Helias Doundoulakis a patent on this approach.
Construction began in the summer of 1960, with the official opening taking place on November 1, 1963. As the primary dish is spherical, its focus is along a line rather than at a single point (as would be the case for a parabolic reflector), thus complicated 'line feeds' had to be used to carry out observations. Each line feed covered a narrow frequency band (2-5% of the center frequency of the band) and a limited number of line feeds could be used at any one time, limiting the flexibility of the telescope.
The telescope has undergone several significant upgrades over its lifespan. The first major upgrade was in 1974 when a high precision surface was added for the current reflector. In 1997 a Gregorian reflector system was installed, incorporating secondary and tertiary reflectors to focus the radio waves at a single point. This allowed the installation of a suite of receivers, covering the whole 1-10GHz range, that could be easily moved onto the focal point, giving Arecibo a flexibility it had not previously possessed. At the same time a ground screen was installed around the perimeter to prevent receivers from sensing the ground (which, due to its temperature, would make observations less sensitive) and a more powerful transmitter was installed.
In August 1989, the observatory directly imaged an asteroid for the first time in history: 4769 Castalia. The following year, Polish astronomer Aleksander Wolszczan made the discovery of pulsar PSR B1257+12, which later led him to discover its three orbiting planets and a possible comet. These were the first extra-solar planets ever discovered. In 1994, John Harmon used the Arecibo radio telescope to map the distribution of ice in the poles of Mercury.
In January 2008, detection of prebiotic molecules methanimine and hydrogen cyanide were reported from Arecibo Observatory radio spectroscopy measurements of the distant starburst galaxy Arp 220.
In 1974, the Arecibo message, an attempt to communicate with extraterrestrial life, was transmitted from the radio telescope toward the globular cluster M13, about 25,000 light-years away. The 1,679 bit pattern of 1s and 0s defined a 23 by 73 pixel bitmap image that included numbers, stick figures, chemical formulas, and a crude image of the telescope itself. Terrestrial aeronomy experiments include the Coqui 2 experiment.
Contributions by the government of Puerto Rico may be one way to help fill the funding gap, but are controversial and uncertain. At town hall meetings about the potential closure, Puerto Rico Senate President Kenneth McClintock announced an initial local appropriation of $3 million during fiscal year 2008 to fund a major maintenance project to restore the three pillars from which the antenna platform is suspended to their original condition, pending inclusion in the next bond issue. The bond authorization, with the $3 million appropriation, was approved by the Senate of Puerto Rico on November 14, 2007, the first day of a special session called by Aníbal Acevedo Vilá. The Puerto Rico House of Representatives repeated this action on June 30, 2008. The Governor signed the measure into law in August 2008.
José Serrano, a member of the U.S. House of Representatives Appropriations Committee, asked the National Science Foundation to keep Arecibo in operation in a letter released on September 19, 2007. Language similar to that in the September 19 letter was included in the FY'08 omnibus spending bill. In October 2007, Puerto Rico's Resident Commissioner, Luis Fortuño, along with Dana Rohrabacher, filed legislation to assure the continued operation of the facility. A similar bill was filed in the United States Senate in April, 2008 by the junior Senator from New York, Hillary Rodham Clinton.
As the Arecibo facility is owned by the United States, and administered as a national facility by the NAIC, direct donations by private or corporate donors cannot be made. However, as a non-profit, non-government institution,Cornell University will accept contributions on behalf of Arecibo Observatory. It has been suggested by at least one member of the NAIC staff that Google purchase advertising space on the dish as one means of securing additional non-government funds.
In September 2007, in an open letter to researchers, the NSF clarified the status of the budget issue for NAIC, stating that the present plan, if implemented, may hit the targeted budgetary revision. No mention of private funding was made. However, it need be noted that the NSF is undertaking studies to mothball, or deconstruct the facility and return it to its natural setting in the event that the budget target is not achieved. In November 2007, The Planetary Society urged Congress to prevent the Arecibo Observatory from closing due to insufficient funds, since the radar contributes heavily to the accuracy of asteroid impact prediction, and they believe continued operation will reduce the cost of mitigation (that is, deflection of NEA on collision to Earth), should that be necessary.
In July 2008, the British newspaper The Daily Telegraph reported that the funding crisis, due to federal budget cuts, was still very much alive. The SETI@home program is using the telescope as a primary source for the research. The program is urging people to send a letter to their political representatives, in support of full federal funding of the observatory.
The film Contact features Arecibo, where the main character uses the facility as part of a SETI project. In the X-Files episode "Little Green Men", Fox Mulder was sent to the Arecibo Observatory by a U.S. Senator because contact had been made with extraterrestrial life. As was often the case in the series, Mulder was forced to escape as U.S. government military forces arrived, without taking definitive proof of alien contact with him. The Arecibo Observatory was also featured in the film Species, as the main setting for the James Gunn novel The Listeners (1972), and as a prominent element in the Mary Doria Russell novel The Sparrow (1996).
Songwriter and author Jimmy Buffett mentions the "giant telescope" in his book Where Is Joe Merchant?, and in the lyrics to the song "Desdemona's Building A Rocket Ship". In both, a talented baker and former backup singer named Desdemona has a tryst with one of the workers "under the giant telescope", and begins receiving telepathic messages from the Pleiades, telling her to build a spaceship and "come home". The dark ambient artist Brian "Lustmord" Williams did an album under the name of Arecibo. The album was titled Trans Plutonian Transmissions. Many of the sounds on Trans Plutonian Transmissions are derived from cosmological activity as recorded by NASA's deep space network.