The Arecibo Observatory is the main facility of the National Astronomy and Ionosphere Center, which is operated by Cornell University under a cooperative agreement with the National Science Foundation.
The main instrument consists of a 305 meter (1000 foot) diameter spherical reflector with a surface made up 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. Each panel can be adjusted to maintain a precise spherical shape that varies less than 0.12 inches over the entire twenty-acre surface. Under the giant dish, vegetation flourishes. Rain and filtered sunlight encourage a lush growth of ferns, grasses, and many other plants, including wild orchids and begonias, which help control erosion. Rainwater drains out of the valley through a natural sink, but an automatic pump is used in times of heavy rainfall.
Suspended 426 feet above the reflector is the 600 ton platform. Similar in design to a bridge, it hangs in midair on eighteen cables: four of these pass directly from each of the three reinforced concrete towers to the apex of the suspended triangle; two others pass from the top of the tower to a point two thirds along the side of the triangle. The tallest of the towers measures 365 feet. Seven more cables run from the top of each tower to massive concrete anchor blocks buried in the ground. Another system of cables runs from each corner of the platform to the ground, to maintain stability.
The cable systems hold the instrument under constant stress and control. Changes in temperature, which are small in Puerto Rico, are automatically compensated for by the cable networks. Under normal wind conditions, the platform barely moves. Strong winds and hurricanes have threatened the lofty structure in the past, but the detectable motion has been quite small. Just below the triangular frame of the upper platform is a circular track, on which the azimuth arm turns.
The azimuth arm is a bowshaped structure 328 feet long. The curved part of the arm is another track, on which the 430 MHz carriage house and the new Gregorian Reflectors inside the large radome can be positioned anywhere up to twenty degrees from the vertical. Hanging below the carriage house are several line-feed antennas, each tuned to a narrow band of frequencies. The antennas point downward and are designed specially for the Arecibo 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 by the enormous radio mirror, that is, the twenty-acre reflector. 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 of observing a given radio source to collect enough energy for analysis whereas at Arecibo this may require just a few minutes of observation. The high sensitivity of the Arecibo main antenna enables scientists to peer more deeply into the universe, and to study the detailed behavior of pulsars which are often not detectable by other telescopes.
Objects in our solar system are studied by analyzing the faint echoes produced when powerful radar beams bounce off their surfaces. When radar radiation is scattered back by plasmas high above our atmosphere (termed incoherent scatter) it provides a tool to study the physical and chemical properties of these regions.
In addition the Observatory maintains a High Frequency (HF) Heating Facility. This Ionospheric Modification Facility consists of thirty-two log-periodic antennas and powerful transmitters capable of concentrating energy in the ionosphere. Located eight miles north of the Observatory, in Islote, the antenna itself covers fifty-eight acres, being able to radiate 800 kilowatts of power in the wavelength region of twenty to a hundred meters. The extremely strong waves from the installation are adequate for heating the electrons in the ionosphere and producing a number of interactions that are studied using the 1,000 foot main telescope, in effect providing a unique capability as a "laboratory" for studies of plasma physics.
The Observatory also maintains an Optical Laboratory with a variety of instrumentation used for the passive study of terrestrial airglow. In addition, a lidar (Light Detection And Ranging) together with a Fabry-Perot interferometer is primarily used to measure neutral winds and temperatures of the middle atmosphere, covering the range between 15 and 60 km altitude. This capability complements that of the incoherent scatter radar, and gives Arecibo a unique capability in the world in terms of aeronomic research.
The main function of the Observatory is that of furthering scientific research in the fields of Radio Astronomy, Planetary Radar, and Atmospheric Sciences. It 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. The scientific activities at the Observatory are at the cutting edge of basic research, and the facility is unique and leading in the world in the disciplines in which it operates.
NAIC Arecibo Home Page - home of the Arecibo Observatory
* Image and text credit: NAIC Arecibo Observatory Home Page.