University of California, San Diego
Center for Astrophysics & Space Sciences

Radio Telescopes

 Radio telescopes can be made much larger than optical/infrared telescopes because the wavelengths of radio waves are much longer than wavelengths of optical light. A rule of thumb is that the reflecting surface must not have irregularities larger than about 1/5 the wavelength of light that is being focused. By that criterion, a radio telescope is several hundred thousand times easier to configure than an optical telescope of the same size.

The Arecibo Observatory radio telescope is a 305 meter reflecting surface in a natural limestone sinkhole in NW Puerto Rico. Because the telescope cannot be pointed independently, the telescope is "steered" by the gregorian instrument housing supported over the telescope.

Interferometry

Because radio signals are detected as waves, signals from different telescopes can be added to simulate or synthesize the resolving capability (pin- pointing) of a much larger telescope. The National Radio Astronomy Observatory's Very Large Array (VLA) near Socorro, NM, consists of 27 radio telescopes, each 25 meters in diameter. They are deployed on a Y-shaped track that can be extended up to 36 km. The VLA has the resolving power of a 36km telescope (but only the collecting-area and sensitivity of a 130m telescope).

Very Long Baseline Interferometry

The Very Long Baseline Array is a global interferometer combining signals from radio telescopes from the Virgin Islands to Hawaii. This is equivalent to a telescope nearly as large as the earth.

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