Arecibo Observatory
The Arecibo Observatory is part of the National Astronomy and Ionosphere Center (NAIC), a national research center operated by Cornell University under a cooperative agreement with the National Science Foundation (NSF). The NSF is an independent federal agency whose aim is to promote scientific and engineering progress in the United States. NSF funds research and education in most fields of science and engineering. Additional support is provided by the National Aeronautics and Space Administration (NASA) Making Arecibo a very important part of the Space exploration for planet.
The Observatory operates on a continuous basis, 24 hours a day every day, providing observing time, electronics, computer, travel and logistic support to scientists from all over the world. All results of research are published in the scientific literature which is publicly available.
As the site of the world's largest single-dish radio telescope, the Observatory is recognized as one of the most important national centers for research in radio astronomy, planetary radar and terrestrial aeronomy. Use of the Arecibo Observatory is available on an equal, competitive basis to all scientists from throughout the world. Observing time is granted on the basis of the most promising research as ascertained by a panel of independent referees who review the proposals sent to the Observatory by interested scientists. Every year about 200 scientists visit the Observatory facilities to pursue their research project, and numerous students perform observations that lead to their master and doctoral dissertations .
Those who see the Arecibo radio telescope for the first time are astounded by the enormousness of the reflecting surface, or radio mirror. The huge "dish" is 305 m (1000 feet) in diameter, 167 feet deep, and covers an area of about twenty acres. The surface is made of almost 40,000 perforated aluminum panels, each measuring about 3 feet by 6 feet, supported by a network of steel cables strung across the underlying karst sinkhole. It is a spherical (not parabolic) reflector .
ARECIBO, Puerto Rico -- It is a space-age sentinel, rising out of the prehistoric jungles of Puerto Rico -- a 1,000-foot (305-meter) diameter aluminum "ear," cocked perpendicular to Earth, leaning into the sky, listening.
For 37 years radio astronomers at the Arecibo Observatory have used this, the world's largest radio telescope, to fathom the radio signals of the cosmos. It has tuned in on the tumultuous songs buried in the hearts of stars and quasars that radiate from the very edge of the universe. Closer to home, it has lent an ear to random radio emissions emanating from 2 miles (3.2 kilometers) within the upper atmosphere.
Located 12 miles (19 kilometers) from the coastal city of Arecibo, the facility requires a full-time staff of 140. Most of them are technicians and engineers, and nearly 30 are astronomers and engineers from countries as different as India, Uruguay, Great Britain, Sweden, Belgium and United States.
"The radio telescope can be used 24 hours a day," says Reinaldo Velez, the observatory's chief telescope technical operator. "Darkness or daylight doesn't make any difference when it comes to radio waves."
Even so, most scientists prefer to work at night, Velez says, as the interference from cell phones, pagers and radar is much less.
With the proliferation of modern electronic devices and communications equipment, electronic interference has is grown worse in recent years. Besides Earth-based technology, communication-satellite constellations like those of the now defunct Iridium, along with powerful military and civilian airport radar also clutter the radio waves.
"It's similar to optical telescopes having to penetrate city air pollution," says Velez, who has been at the observatory 26 years. "It's a constant battle we cannot win."
However, the assault on Arecibo comes on two fronts -- while electronic emissions encroach from the air, on the ground of this former 15 th -century Spanish colony in the Caribbean, the tropical forest forever attempts to consume the structure.
"Sometimes, up to three days a week, the radio telescope is shut down because technicians have essentially to beat back the jungle," says Mike Nolan, a planetary radar scientist.
Most of the engineers compare the facility to a ship exposed to natural marine threats: tropical heat, luxuriant vegetation, fungi and salty air all can create rust and other harsh effects on the fine electronics and complex mechanisms. The observatory's smooth operations depend on 26 electrical motors and 30 miles (48 kilometers) of thick cables supporting the 900-ton reflector suspended 450 feet (137 meters) above the radio telescope's metallic dish.
Even under the observatory's spherical dish, 1,000 feet in diameter (305 meters) and suspended from 20-foot- (6-meter-) long cables, an abundant and colorful life flourishes. While deterring erosion of the limestone terrain, a lush growth of ferns, begonias and wild orchids have to be trimmed on a regular basis to keep them from interfering with the 18-acre surface of the bowl-shaped reflector. Composed of 40,000 aluminum panels, this antenna covers the same area as 26 football fields.
Suspended 450 feet above the reflector is the 900 ton platform. Similar in design to a bridge, it hangs in midair on eighteen cables, which are strung from three reinforced concrete towers. One is 365 feet high, and the other two are 265 feet high. All three tops are at the same elevation. The combined volume of reinforced concrete in all three towers is 9,100 cubic yards. Each tower is back-guyed to ground anchors with seven 3.25 inch diameter steel bridge cables. Another system of three pairs of cables runs from each corner of the platform to large concrete blocks under the reflector. They are attached to giant jacks which allow adjustment of the height of each corner with millimeter precision. Just below the triangular frame of the upper platform is a circular track on which the azimuth arm turns. The azimuth arm is a bow shaped structure 328 feet long. The curved part of the arm is another track, on which a carriage house on one side and the gregorian dome (installed in 1996) on the other side can be positioned anywhere up to twenty degrees from the vertical. Inside the gregorian dome two subreflectors (secondary and tertiary) focus radiation to a point in space where a set of horn antennae can be positioned to gather it. Hanging below the carriage house are various linear antennas each tuned to a narrow band of frequencies. The antennas point downward and are designed specially for the Arecibo spherical reflector. By aiming a feed antenna at a certain point on the reflector, radio emissions originating from a very small area of the sky in line with the feed antenna will be focused on the feed antenna.
Attached to the antennas are very sensitive and highly complex radio receivers. These devices operate immersed in a bath of liquid helium, to maintain a very low receiver temperature. At such cold temperatures the electron noise in the receivers is very small, and only the incoming radio signals, which are very weak, are amplified. The Arecibo system operates at frequencies from 50 megahertz (6 m wavelength) up to 10,000 megahertz (3 cm wavelength). 
A total of 26 electric motors control the platform. These motors drive the azimuth and the gregorian dome and carriage house to any position with millimeter precision. The tertiary reflector can be moved to improve focusing, receivers are moved into focus on a rotating floor inside the gregorian and the dynamical tie downs activate as needed to maintain platform position. The 1 MW planetary radar transmitter located in a special room inside the dome, directs radar waves to objects in our solar system. Analyzing the echoes provides information about surface properties and object dynamics.
This giant telescope has scrutinized our atmosphere from a few kilometers to a few thousand kilometers where it smoothly connects with interplanetary space. With its radar vision it studies the properties of planets, comets and asteroids. In our Galaxy it detects the faint pulses emitted hundreds of times per second from pulsars. And from the farthest reaches of the Universe quasars and galaxies emit radio waves which arrive at earth 100 million years later as signals so weak that they can only be detected by a giant eye like this one.
The giant size of the reflector is what makes the Arecibo Observatory so special to scientists. It is the largest curved focusing antenna on the planet, which means it is the world's most sensitive radio telescope. Other radio telescopes may require several hours observing a given radio source to collect enough energy for analysis whereas at Arecibo this may require just a few minutes of observation.
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