RATAN-600

thumb|upright|One of the conical secondary reflectors of the RATAN-600 on a 1987 USSR [[postal stamp ]]

The RATAN-600 (, an acronym for the "Academy of Sciences Radio Telescope – 600") is a radio telescope in Zelenchukskaya, Karachay–Cherkess Republic, Russia. It comprises a 576 m diameter circle of rectangular radio reflectors and a set of secondary reflectors and receivers, based at an altitude of 970 m. Each of the 895 2×7.4 m reflectors can be angled to reflect incoming radio waves towards a central conical secondary mirror, or to one of five parabolic cylinders. Each secondary reflector is combined with an instrumentation cabin containing various receivers and instruments. The overall effect is that of a partially steerable antenna with a maximum resolving power of a nearly 600 m diameter dish, when using the central conical receiver, making it the world's largest-diameter individual radio telescope. It began operation in 1977.