radar astronomy

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radar astronomy application of radar to the determination of distances and planetary features within the solar system, such as rotation rates. A short burst of radio waves is transmitted in the direction of the object under study. The object reflects the radio waves back to earth, where they are detected by the same antenna that sent the signal. The time between sending the signal and receiving the "echo" can be precisely measured electronically. Since radio waves travel with the speed of light, the roundtrip distance from the earth to the object and back is then easily computed. This technique differs from radio astronomy in that the celestial object is here merely a passive reflector, rather than the actual source of the emission. The first yield of radar astronomy was a much improved value for the distance from the earth to the moon. Using more powerful transmitters, the distances to Venus and Mercury were also measured, as well as the planets' rotational periods and gross surface properties. Even greater precision is obtained by replacing the radio transmitter with a laser . During the Apollo project, special reflectors were installed on the moon; subsequently, by bouncing laser light off the moon the distance from the earth to the moon could be determined within centimeters. Radar observations are also useful for asteroids and comets whose orbits take them relatively near the earth. Much of the surface of Venus has been mapped by unmanned probes using radar altimeters to penetrate the cloud cover.

radar astronomy The study of bodies in the Solar System by reflecting radio pulses off them. Radar work requires very large (and hence sensitive) telescopes, such as the 305-m radio dish at Arecibo Observatory. Radar astronomy can be used to determine the accurate distances of the planets (by measuring the time delay of the reflected signal), rotation rates (by Doppler broadening of the signal), and to map surface features (by detailed analysis of the echoes). Notable achievements in radar astronomy include the accurate measurement of the astronomical unit; determination of the rotation periods of Mercury and Venus; and the mapping of the cloud-covered surface of Venus. Earth-based radar has also been used to study the surface of Mars, the larger moons of Jupiter and Saturn, the rings of Saturn, asteroids, comets, and meteor trails. Several spacecraft sent to Venus have carried radar mapping equipment, notably Pioneer Venus Orbiter, Veneras 15 and 16, and Magellan.

radar astronomy Branch of astronomy in which radar pulses, reflected back to Earth from celestial bodies in our solar system, are studied for information concerning their distance from Earth, their orbital motion, and large surface features. Techniques developed for radar mapping of planetary surfaces have proved particularly important for cloud-covered Venus.