Arecibo Observatory

The Arecibo Observatory is a radio telescope in the municipality of Arecibo, Puerto Rico. This observatory is operated by University of Central Florida, Yang Enterprises and UMET, under cooperative agreement with the US National Science Foundation (NSF). The observatory is the sole facility of the National Astronomy and Ionosphere Center (NAIC), which is the formal name of the observatory. From its construction in the 1960s until 2011, the observatory was managed by Cornell University.

For more than 50 years, from its completion in 1963 until July 2016 when the Five hundred meter Aperture Spherical Telescope (FAST) in China was completed, the Arecibo Observatory's 1,000-foot (305-meter) radio telescope was the world's largest single-aperture telescope. It is used in three major areas of research: radio astronomy, atmospheric science, and radar astronomy. Scientists who want to use the observatory submit proposals that are evaluated by an independent scientific board.

The observatory has appeared in film, gaming and television productions, gaining more recognition in 1999 when it began to collect data for the SETI@home project. It has been listed on the US National Register of Historic Places starting in 2008. It was the featured listing in the US National Park Service's weekly list of October 3, 2008. The center was named an IEEE Milestone in 2001. It has a visitor center that is open part-time.

On September 21, 2017, high winds associated with Hurricane Maria caused the 430 MHz line feed to break and fall onto the primary dish, damaging about 30 out of 38,000 aluminum panels. Most Arecibo observations do not use the line feed but instead rely on the feeds and receivers located in the dome. Overall, the damage inflicted by Maria was minimal.

General information

The main collecting dish is 305 m (1,000 ft) in diameter, constructed inside the depression left by a karst sinkhole. The dish surface is made of 38,778 perforated aluminum panels, each about 3 by 6 feet (1 by 2 m), supported by a mesh of steel cables. The ground beneath is accessible and supports shade-tolerant vegetation.

The observatory has four radar transmitters, with effective isotropic radiated powers of 20 TW (continuous) at 2380 MHz, 2.5 TW (pulse peak) at 430 MHz, 300 MW at 47 MHz, and 6 MW at 8 MHz.

The reflector is a spherical reflector, not a parabolic reflector. To aim the device, the receiver is moved to intercept signals reflected from different directions by the spherical dish surface of 270 m (870 ft) radius. A parabolic mirror would have varying astigmatism when the receiver is off the focal point, but the error of a spherical mirror is uniform in every direction.

The receiver is on a 900-ton platform suspended 150 m (492 ft) above the dish by 18 cables running from three reinforced concrete towers, one 111 m (365 ft) high and the other two 81 m (265 ft) high, placing their tops at the same elevation. The platform has a rotating, bow-shaped track 93 m (305 ft) long, called the azimuth arm, carrying the receiving antennas and secondary and tertiary reflectors. This allows the telescope to observe any region of the sky in a forty-degree cone of visibility about the local zenith (between −1 and 38 degrees of declination). Puerto Rico's location near the Northern Tropic allows Arecibo to view the planets in the Solar System over the Northern half of their orbit. The round trip light time to objects beyond Saturn is longer than the 2.6 hour time that the telescope can track a celestial position, preventing radar observations of more distant objects.