radio astronomy: Radio Telescopes

Radio waves emanating from celestial bodies are received by specially constructed antennas, called radio telescopes, whose use corresponds to that of the optical telescope in observing visible light. In the most common design, a parabolic “dish” replaces the mirror of the reflecting optical telescope. This dish serves to focus the radio waves into a concentrated signal that is then filtered, amplified, and finally analyzed using a computer. The radio signals received from outer space are extremely weak, and long observing times are required to collect a useful amount of energy. Therefore, most radio telescopes are mounted so that they can automatically track a given object as its position changes because of the rotation of the earth. Multiple radio antennas, in some cases located hundreds of miles from each other, may be used together in arrays. The observations made by the antennas are combined by computer to provide the equivalent power of a radio dish 10 mi (16 km) or more in diameter. Specialized radio astronomy satellites are used to make observations at wavelengths that are subject to distortion or interference before they reach the earth's surface.

Sections in this article:

• Introduction
• Extragalactic Sources of Radio Waves
• Galactic Sources of Radio Waves
• Radio Telescopes
• Bibliography

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