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Arecibo, short for the Arecibo Observatory, is a radio telescope, located close to Arecibo, Puerto Rico. It is operated by Cornell University and the National Science Foundation. It is also called the National Astronomy And Ionosphere Center(NAIC). The radio telescope is 305m in diameter and is the largest single-aperture telescope ever constructed. It does three types of research: radio astronomy, aeronomy, and radar astronomy.
The Arecibo telescope is constructed inside the depression left by a karst sinkhole.(shaped by the dissolution of a layer or layers of soluble bedrock). The dish is the largest curved focusing dish on Earth, giving Arecibo the largest electromagnetic-wave-gathering capacity. The telescope’s dish surface is made of 38,778 aluminum panels, each measuring about 1×2 meters, supported by a mesh of steel cables. It has three radar transmitters, with effective isotropic radiated powers of 20 TW at 2380 MHz, 2.5 TW at 430 MHz, and 300 MW at 47 MHz.
Arecibo is a spherical reflector. This is due to the method used to aim the telescope: the telescope’s dish is fixed in place, and the receiver is repositioned to intercept signals reflected from different directions by the spherical dish surface. The receiver is positioned on a 900-ton platform, suspended 150 m above the dish by cables running from multiple reinforced concrete towers. The platform has a 93-meter-long rotating bow-shaped track(azimuth arm) where receiving antennas, 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 zenith. The telescope’s location close to the equator allows it to view all of the planets in the solar system. The drawback is that the round trip time for light to travel to objects beyond Saturn is longer than the time the telescope can track it, so it is prevented from making radar observations of objects beyond Saturn.
Arecibo has had several uses and discoveries over its lifetime. In April, 1964 it was used to determine that the rotation of Mercury is only 59 days. In 1968, the discovery of the periodicity of the Crab Pulsar provided the first solid evidence that neutron stars exist. The first millisecond pulsar was discovered in 1982. This object, PSR B1937+21, spins 642 times per second. In 1990, it was used to discover the first known extra-solar planets. As usual, the military usurped scientific observation, so the telescope was used to locate Soviet radar installations by detecting their signals as the bounced off the Moon. Arecibo is also the source of data for the SETI program and, in 1974, an attempt to communicate with extraterrestrial life was transmitted from the radio telescope toward the globular cluster M13. 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. Hopefully, we will get a response in the future.
We have written many articles about the Arecibo Telescope for Universe Today. Here’s an article about the Arecibo Observatory, and here’s an article about the triple asteroid spotted by the Arecibo Telescope.
If you’d like more info on the Arecibo Radio Telescope, check out the NASA Educational Show to Feature the Arecibo Observatory, and here’s a link to Arecibo: The Largest Telescope in the World.
We’ve also recorded an entire episode of Astronomy Cast all about the Telescopes. Listen here, Episode 150: Telescopes, The Next Level.