|H. E. Smith||Winter 2007|
|Physics 7 Lecture Summary #4
Radio telescopes may 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 figure 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.|
Because radio signals are detected as waves, signals from different telescopes can be added to simulate or synthesize the resolving or pin-pointing capability 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 which are deployed on a Y-shaped track which may be extended up to 36km. 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 with radio telescopes from the Virgin Islands to Hawaii, synthesizing a radio telescope nearly as large as the earth.
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Last updated: 12 January 2001