Arecibo Observatory

The Arecibo Observatory (AO) is a research center operated by SRI International, USRA and UMET, 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)

The AO 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 second 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 AO 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.

The AO had its origins in an idea of Professor William E. Gordon, then of Cornell University, who was interested in the study of the Ionosphere. Gordon's research during the fifties led him to the idea of radar back scatter studies of the Ionosphere. Gordon's persistence culminated in the construction of the AO which began in the Summer of 1960. Three years later the Arecibo Ionospheric Observatory (AIO) was in operation under the direction of Gordon. The formal opening ceremony took place on November 1, 1963.

From the beginning there were certain requirements for the site. 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.

In addition an Optical Laboratory with a variety of instrumentation used for the passive study of terrestrial airglow is located at the Observatory. 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 This capability complements that of the incoherent scatter radar, and gives Arecibo a unique capability in the world in terms of aeronomic

"If you dream, have big dreams and have talented supporters to help you”

William "Bill" Gordon

AO Overview
Telescope Description
Frequently Asked Questions

Generous Supporters

With your online contribution, you can support
the continuous improvement of the Arecibo Observatory.


“Toward 2025 the Arecibo Observatory (AO) will continue to be recognized as a world-leading radio astronomy, solar system radar and atmospheric physics facility, contributing highly relevant data to support discovery, innovation and the advancement of science for the well-being of human kind. AO will establish a world-class informal educational program, supporting K-16 and PhD-level studies, to stimulate and promote new generations of scientists and engineers at national level, while also contributing to the economic and social development of Puerto Rico”


The AO enables research in the areas of astronomy, planetary studies, and space and atmospheric sciences by providing unique capabilities and state-of-the-art instrumentation for data collection and analysis, together with logistical support to users. AO initiates and supports progress in the above research areas by maintaining a scientific staff whose members develop individual research programs, provide assistance to visiting scientists, and extend available scientific opportunities by developing and implementing plans for future enhancements to AO facilities and instrumentation.

AO contributes to the general understanding and appreciation of science by initiating and participating in public education and outreach programs. Use of the AO is available on an equal, competitive basis to all scientists from throughout the world to pursue research in astronomy, planetary studies and space and atmospheric sciences. Observing time is granted on the basis of the most promising research, as ascertained by peer review of proposals by external referees.

Research Distribution

13% Planetary Studies
Space & Atmospheric Studies 22%
Pulsar Astronomy40%
Radio Astronomy 20%
Other 5%

Heads of Groups