Arecibo Observatory

**Arecibo radio telescope**
Physical Characteristics

Organization	Cornell, NSF
Location	Arecibo, Puerto Rico
Wavelength regime	radio
Completion date	1963
Webpage	www.naic.edu
Telescope Style	spherical reflector
Diameter	305 m
Collecting Area	~73,000 m²
Focal Length	(fill in)
Mounting	transit instrument: fixed primary with secondary (Gregorian reflectors) on tracks for pointing
Dome	none
Geographical Coordinates	Template:Coor dms (Geodetic)

The Arecibo Observatory is located in Arecibo, Puerto Rico on the north coast of the island. 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.

The observatory's radio telescope is the largest single telescope ever to be constructed. It collects radio astronomy, terrestrial aeronomy, and planetary radar data for scientists around the world. Usage of the telescope is gained by submitting proposals to an independent board of referees who decide which show the most promise.

Although it has been given many usages, the observatory's main purpose is to detail and observe stellar objects.

The telescope is visually distinctive and has been used in the filming of two notable movies: as the villain's antenna in the James Bond movie GoldenEye and as the real antenna in the movie Contact. The telescope received international recognition after it was used in 1999 to collect data for the SETI@home project.

Contents

1 General information

2 Design and architecture

3 Discoveries

4 Usage

5 Related topics

6 Arecibo Observatory in Popular Culture

7 External links

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 aluminium 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.

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 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.

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 ground screen was installed around the perimeter to shield from ground radiation and a more powerful transmitter was installed.

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 August of 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 two orbiting planets. These were the first extra-solar planets ever discovered.

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 was also the source of data for the SETI@home distributed computing project put forward by the SETI Institute.

In 1974, an attempt was made to send a message to other worlds. A 1,679 bit message was transmitted from the radio telescope toward the globular cluster M13, about 25,000 light-years away. The 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.

From March 3 to 7, 2001 the observatory was used to observe asteroid (29075) 1950 DA, considered to be the most Near-Earth object.