Arecibo Observatory

Named after city in Puerto Rico


Valley in Arecibo, Puerto Rico.It had to be near the equator, since there, a radar capable of studying the ionosphere could also be used to study nearby planets which pass overhead. The Arecibo site offered the advantage of being located in Karst terrain, with large limestone sinkholes which provided a natural geometry for the construction of the 305 meter reflector.

About the observatory

The Arecibo Observatory captures radio waves. The telescope is currently the largest single-dish telescope in the world. It's made up of 40,000 individual panels. Incoming rays are reflected back from the surface to two additional reflectors located 450 feet above on the "platform", a 500 ton structure supported by cables from three towers.

More on how it works

Incoming rays are reflected first off the fixed reflector on the bottom of the sinkhole are reflected up to the secondary and then to the tertiary mirror. They finally come to a point of focus at the receiver room. Feeds attached to different receivers, covering different frequency (wavelength) ranges, can be moved into position at the focal point because they sit on a rotating turntable in the receiver room.


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Major Discoveries

  • The first planets outside the solar system were discovered around Pulsar B1257+12, a rapidly rotating pulsar with three Earth-like planets in orbit. ( early 1990s )
  • One of its first accomplishments: Establishing the rotating rate of Mercury, which turned out to be 59 days rather than the previously estimated 88 days ( 1965 ).
  • Detailed maps of the distribution of galaxies in the universe ( late 1980s ).
  • The first pulsar in a binary system was discovered ( 1974 ), leading to important confirmation of Einstein's theory of general relativity and a Nobel Prize for astronomers Russell Hulse and Joseph Taylor ( 1993 ).
  • Investigations of ice craters at the polar regions of the planet Mercury with the radar system ( 1990s ) and similar investigation of the lunar poles for evidence of ice ( 1997 ).

Current Changes

An oversight committee for Arecibo Observatory has been established to act as a management link between Cornell University, which manages the huge radio telescope, and the U.S. funding agency, the National Science Foundation (NSF).


Many meteorological services located in the United States make use of the data collected by the radio telescopes present at this observatory.