An instrument for collecting and measuring radio waves from astronomical sources. Single-dish radio telescopes can be either used alone or joined into interferometers and arrays. Single-dish telescopes usually have a parabolic reflector, which works in a similar way to the main mirror of an optical telescope. Because radio waves are much longer than light waves, radio reflectors need have only relatively moderate surface accuracy. But, for the same reason, even the largest single-dish radio telescopes cannot match the angular resolution of optical telescopes. Radio interferometers, made of two or more spaced antennas (elements) connected together, are used to achieve high angular resolution. Resolutions better than 0″.001 can be achieved in this way, far exceeding the performance of even the Hubble Space Telescope. Aperture synthesis telescopes are interferometers in which the whole or part of a large, imaginary aperture is built up by the rotation of the Earth and, in some cases, by the movement of the dishes. Parabolic dishes are normally steerable, the larger ones being on altazimuth mountings, but many interferometers consist of arrays of static antennas which either have a fixed beam or can be steered electronically.
Subjects: Astronomy and Astrophysics — Physics.