Arecibo Observatory
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| Arecibo Radio Telescope | |
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| Organization: | Cornell, NSF, NASA |
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| Location: | Arecibo, Puerto Rico |
| Wavelength: | radio (3 cm-1 m) |
| Built: | 1963 |
| Telescope style: | spherical reflector |
| Diameter: | 305 m, 1000ft |
| Collecting area: | ~73 000 m², ~790 000 ft², ~18 acres |
| Focal length: | 132.5 m, 434.7ft |
| Mounting: | transit instrument: fixed primary with secondary (Gregorian reflectors) on tracks for pointing |
| Dome: | none |
| Website: | www.naic.edu |
The Arecibo Observatory is located approximately 9 miles south-southwest from Arecibo, Puerto Rico (near the extreme southwestern corner of Arecibo pueblo). It is operated by Cornell University under cooperative agreement with the National Science Foundation. The observatory works as the National Astronomy and Ionosphere Center (NAIC) although both names are officially used to refer to it. NAIC more properly refers to the organization that runs both the observatory and associated offices at Cornell University.
The observatory's 305-m radio telescope is the largest single-aperture telescope (cf. multiple aperture telescope) ever to be 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 observations of solar system objects. Usage of the telescope is gained by submitting proposals to an independent board of referees.
The telescope is visually distinctive and has been used in the filming of two notable motion pictures: as the villain's antenna in the James Bond movie GoldenEye and as itself in the film Contact. The telescope received additional international recognition in 1999 when it began to collect data for the SETI@home project.
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[edit] General information
The Arecibo telescope is distinguished by its enormous size: the main collecting dish is 305 m in diameter, constructed inside the depression left by a karst sinkhole. The dish is the largest curved focusing dish on Earth, giving Arecibo the largest electromagnetic-wave gathering capacity. The Arecibo telescope's dish surface is made of 38,778 perforated aluminum panels, each measuring about 1 m by 2 m (3 ft by 6 ft), supported by a mesh of steel cables.
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, but the receiver at its focal point is repositioned to intercept signals reflected from different directions by the spherical dish surface. The receiver is located on a 900-ton platform which is suspended 150 m (450 ft) in the air above the dish by 18 cables running from three reinforced concrete towers, one of which is 110 m (365 ft) 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 antennae, 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.
[edit] Design and architecture
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 150 m (500 ft) 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 of 1959. 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 1-10 GHz 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.
[edit] Discoveries
The Arecibo telescope has made many significant scientific discoveries. On 7 April 1964, shortly after its inauguration, Gordon H. Pettengill's team used it to determine that the rotation rate of Mercury was not 88 days, as previously thought, but only 59 days. In 1968, the discovery of the periodicity of the Crab Pulsar (33 ms) by Lovelace and others provided the first solid evidence that neutron stars exist in the Universe. In 1974 Hulse and Taylor discovered the first binary pulsar PSR B1913+16, for which they were later awarded the Nobel Prize in Physics. In 1982, the first millisecond pulsar, PSR J1937+21, was discovered by Don Backer, Shri Kulkarni and others. This object spins 642 times per second, and it was until 2005 the fastest-spinning pulsar known.
In August 1989, the observatory directly imaged an asteroid for the first time in history: asteroid 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.
[edit] Other usage
The telescope also had military intelligence uses, for example locating Soviet radar installations by detecting their signals bouncing back off of the Moon. Arecibo is also the source of data for the SETI@home distributed computing project put forward by the Space Sciences Laboratory at the University of California, Berkeley and was used for the SETI Institute's Project Phoenix observations.
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 controversial (Ruiz 1998) Coqui 2 experiment (Friedlander 1997).
[edit] Arecibo in popular culture
Arecibo Observatory was used as a filming location in the final scene of the James Bond movie GoldenEye. In the film, the villain Alec Trevelyan used a similar dish in Cuba to communicate with a Russian satellite to fire an electromagnetic pulse at London. This dish could be filled with water to conceal itself as a lake, a feat impossible at Arecibo due to its perforated surface. Additionally, the use of Arecibo to communicate with an earth-orbiting satellite is nonsensical from a technical standpoint.
The observatory was also featured in a segment of a Reading Rainbow episode.
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 film Contact features Arecibo in a more life-like way, as main character Ellie Arroway uses the facility as part of a SETI project.
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).
The aliens in the BBC radio serial Space Force (1984) contact Earth after receiving the Arecibo message. One of the characters in the episode "The Voice from Nowhere" says that the Arecibo Observatory was closed down and dismantled.
[edit] Threatened Closure
A report by the National Science Foundation, made public on 2006-11-03, recommended decreased funding for Arecibo Observatory. If other sources of funding cannot be obtained, the telescope will be shut down in 2011. The report also advised that 80% of the observation time be allocated to the surveys already in progress, reducing the time available for other scientific work. If the report's recommendations are followed, Arecibo's radar astronomy program will cease October 1 2007.
[edit] See also
- List of radio telescopes
- Sixto Gonzalez, former director of Arecibo Observatory
- Arecibo message
[edit] References
- Friedlander, Blaine P. Jr.. "Research rockets, including an experiment from Cornell, are scheduled for launch into the ionosphere next year from Puerto Rico", Cornell University, 1997-11-14.
- Ruiz, Carmelo. "Activists protest US Navy radar project", Global Network Against Weapons and Nuclear Power in Space, 1998-03-03.
- From the Ground Up: Balancing the NSF Astronomy Program (2006-10-22). Retrieved on November 6, 2006.
[edit] External links
- Arecibo Observatory official site
- SETI@home official site
- IEEE History Center - IEEE Milestones: NAIC/Arecibo Radiotelescope
- Lofar
- Google Maps
