“radio telescope”的概念、定义、翻译、参考文献-科学参考

radio telescope

Physics

An instrument for detecting and measuring electromagnetic radiation of radio frequencies that have passed through the radio window in the earth’s atmosphere and reached the surface of the earth. There are a great diversity of radio sources within the universe and radio telescopes are required to detect both continuous emissions and specific spectral lines. They therefore require the highest possible angular resolution so that the details of radio sources can be studied and they should be able to pick up weak signals. The simplest radio telescope consists of a paraboloidal steerable-dish aerial together with ancillary amplifiers. The paraboloidal reflecting dish surface reflects the incoming signal to the principal focus of the reflector. At this point the radio-frequency signals are amplified up to 1000 times and converted to a lower, intermediate, frequency before transmission by cable to the control building. Here the intermediate frequency is amplified again and passed to the detector and display unit. As the radio waves arriving from the surface of the reflector at the focus must be in phase, the surface of the dish must be very accurately constructed; for example, a 100-metre-diameter dish must be accurate to the nearest millimetre, when receiving radiation of 1 cm wavelength. To overcome the problem of constructing large dishes to such a high accuracy, the technique of radio interferometry has been developed. In this technique an array of small aerials connected by cable is used to simulate a large dish aerial. In earth-rotation aperture synthesis, the individual positions and displacements of an array of only a few such small aerials can be made to simulate an enormous dish aerial as the earth rotates. All but the smallest steerable dishes are constructed from metal mesh so that wind can pass through them. A few very large fixed dishes have been built into the earth’s surface.

Astronomy

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 usually being on altazimuth mountings. The largest single dishes in the world, the Five-hundred-meter Aperture Spherical Telescope (500 m) in China and Arecibo (305 m) in Puerto Rico, are built in natural hollows in the ground and act as transit telescopes, with some steering provided by sub-reflectors. At long wavelengths many interferometers consist of arrays of static antennas which either have a fixed beam or can be steered electronically (phased arrays).

Space Exploration

An instrument for detecting radio waves from the universe in radio astronomy. Radio telescopes usually consist of a metal bowl that collects and focuses radio waves the way a concave mirror collects and focuses light waves. Radio telescopes are much larger than optical telescopes, because the wavelengths they are detecting are much longer than the wavelength of light. The largest single dish, 305 m in diameter, is at Arecibo Observatory, Puerto Rico.
A large dish such as that at Jodrell Bank, Cheshire, England, can see the radio sky less clearly than a small optical telescope sees the visible sky.
Interferometry is a technique in which the output from two dishes is combined to give better resolution of detail than with a single dish.
Very long baseline interferometry (VBLI) uses radio telescopes spread across the world to resolve minute details of radio sources.
In aperture synthesis, several dishes are linked together to simulate the performance of a very large single dish. This technique was pioneered by English radio astronomer Martin Ryle at the Mullard Radio Astronomy Observatory, Cambridge, England, site of a radio telescope consisting of eight dishes in a 5-km line. The Very Large Array in New Mexico consists of 27 dishes arranged in a Y-shape, which simulates the performance of a single dish 27 km in diameter. Other radio telescopes are shaped like long troughs, and some consist of simple rod-shaped aerials.

Electronics and Electrical Engineering

A telescope used in radio astronomy to record and measure extraterrestrial radio signals. It consists of an antenna, or system of antennas, connected by feeders to one or more receivers, where the signals are amplified and analysed, usually by a computer. The antennas may be in the form of dishes, linear dipoles, or Yagi antennas. A dish is a large generally parabolic metal reflector that brings radiowaves to a focus above the dish centre. The focused waves are collected by a secondary feed antenna that is connected to the receiver. Dishes can usually be steered to point to different regions of the sky.
The antenna system may form a radio interferometer, in which the electrical signals from two separated antenna units are fed to a common receiver. The antenna units are often mounted on an E–W line, pointing in the same direction, so that the earth’s rotation causes an extraterrestrial radio source to move through the antenna beam. The two identical signals from the antenna units travel a different pathlength; when combined, the amplitude of the summed signal changes periodically producing interference fringes at the receiver output. An interferometer is generally used to improve the resolution of the telescope, i.e. to allow finer detail to be distinguished. Analysis of the fringes allows the structure of a radio source to be determined.

单词	radio telescope
释义	radio telescope Physics An instrument for detecting and measuring electromagnetic radiation of radio frequencies that have passed through the radio window in the earth’s atmosphere and reached the surface of the earth. There are a great diversity of radio sources within the universe and radio telescopes are required to detect both continuous emissions and specific spectral lines. They therefore require the highest possible angular resolution so that the details of radio sources can be studied and they should be able to pick up weak signals. The simplest radio telescope consists of a paraboloidal steerable-dish aerial together with ancillary amplifiers. The paraboloidal reflecting dish surface reflects the incoming signal to the principal focus of the reflector. At this point the radio-frequency signals are amplified up to 1000 times and converted to a lower, intermediate, frequency before transmission by cable to the control building. Here the intermediate frequency is amplified again and passed to the detector and display unit. As the radio waves arriving from the surface of the reflector at the focus must be in phase, the surface of the dish must be very accurately constructed; for example, a 100-metre-diameter dish must be accurate to the nearest millimetre, when receiving radiation of 1 cm wavelength. To overcome the problem of constructing large dishes to such a high accuracy, the technique of radio interferometry has been developed. In this technique an array of small aerials connected by cable is used to simulate a large dish aerial. In earth-rotation aperture synthesis, the individual positions and displacements of an array of only a few such small aerials can be made to simulate an enormous dish aerial as the earth rotates. All but the smallest steerable dishes are constructed from metal mesh so that wind can pass through them. A few very large fixed dishes have been built into the earth’s surface. Astronomy 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 usually being on altazimuth mountings. The largest single dishes in the world, the Five-hundred-meter Aperture Spherical Telescope (500 m) in China and Arecibo (305 m) in Puerto Rico, are built in natural hollows in the ground and act as transit telescopes, with some steering provided by sub-reflectors. At long wavelengths many interferometers consist of arrays of static antennas which either have a fixed beam or can be steered electronically (phased arrays). Space Exploration An instrument for detecting radio waves from the universe in radio astronomy. Radio telescopes usually consist of a metal bowl that collects and focuses radio waves the way a concave mirror collects and focuses light waves. Radio telescopes are much larger than optical telescopes, because the wavelengths they are detecting are much longer than the wavelength of light. The largest single dish, 305 m in diameter, is at Arecibo Observatory, Puerto Rico. A large dish such as that at Jodrell Bank, Cheshire, England, can see the radio sky less clearly than a small optical telescope sees the visible sky. Interferometry is a technique in which the output from two dishes is combined to give better resolution of detail than with a single dish. Very long baseline interferometry (VBLI) uses radio telescopes spread across the world to resolve minute details of radio sources. In aperture synthesis, several dishes are linked together to simulate the performance of a very large single dish. This technique was pioneered by English radio astronomer Martin Ryle at the Mullard Radio Astronomy Observatory, Cambridge, England, site of a radio telescope consisting of eight dishes in a 5-km line. The Very Large Array in New Mexico consists of 27 dishes arranged in a Y-shape, which simulates the performance of a single dish 27 km in diameter. Other radio telescopes are shaped like long troughs, and some consist of simple rod-shaped aerials. Electronics and Electrical Engineering A telescope used in radio astronomy to record and measure extraterrestrial radio signals. It consists of an antenna, or system of antennas, connected by feeders to one or more receivers, where the signals are amplified and analysed, usually by a computer. The antennas may be in the form of dishes, linear dipoles, or Yagi antennas. A dish is a large generally parabolic metal reflector that brings radiowaves to a focus above the dish centre. The focused waves are collected by a secondary feed antenna that is connected to the receiver. Dishes can usually be steered to point to different regions of the sky. The antenna system may form a radio interferometer, in which the electrical signals from two separated antenna units are fed to a common receiver. The antenna units are often mounted on an E–W line, pointing in the same direction, so that the earth’s rotation causes an extraterrestrial radio source to move through the antenna beam. The two identical signals from the antenna units travel a different pathlength; when combined, the amplitude of the summed signal changes periodically producing interference fringes at the receiver output. An interferometer is generally used to improve the resolution of the telescope, i.e. to allow finer detail to be distinguished. Analysis of the fringes allows the structure of a radio source to be determined.
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