- telescope used to observe the radio sky. Radio telescopes look profoundly different from optical ones. Most resemble radar or satellite communications dishes instead, although older-fashioned types use extensive wire antennae. The dish types work by scooping up incoming radiation from the sky and bringing it to a focus where it can be recorded. The signals received can be amplified many billions of times, or added to those received from other radio telescopes for interferometry. Because of the rise of interferometry as a technique, few new radio telescopes are being built in the form of single large dishes, and instead arrays (such as the Very Large Array in the US) are the pattern. But single receivers are still being built for use in unusual frequencies, like the James Clerk Maxwell Telescope on Hawaii, designed for use in submillimetre wavelength astronomy.
- An instrument which detects, amplifies, and analyses radio waves originating outside the earth's atmosphere. A radio telescope incorporates one or more parabolic reflectors or other highly directional antennas, very sensitive receivers, and computers which analyze the detected signals, which are then displayed and/or recorded. Since radio wavelengths are much longer than those of visible light, such telescopes tend to be rather large when capable of detecting extremely weak radio sources.