RATAN-600 (short for Radio Astronomical Telescope of the Academy of Sciences) is a radio telescope located near the village of Zelenchukskaya in the Caucasus Mountains, in Russia, at an altitude of 970 meters. Unlike most radio telescopes that utilizes a dish or an array of dishes to focus electromagnetic radiation on to a receiver or receivers, RATAN-600 employs a ring of adjustable reflecting panels which can be angled to direct the radiation from any point in the sky to a central conical receiver. Although the ring is only 576 meters in diameter, and there is no solid structure, the overall effect of the arrangement is that of a partially steerable antenna with the resolving power of a 600 meter diameter dish, making it the world's largest diameter individual radio telescope.

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The RATAN-600 is the world’s first multi-element-reflector radio telescope without any structure linking the surface elements. The functions normally performed by such structure are instead, executed by the Earth's rotation. The telescope supplies about one-quarter of all the observational material in Russia in the field of radio astronomy and more than 80% in the central, centimeter-decimeter range, is described.

One special capability of RATAN-600 is its frequency agility — the ability to quickly shift its operating frequency — allowing the telescope to scan a source over a range of frequencies in a very short time. It can make radio frequency observations in the frequency band ranging from 610 MHz to 30 GHz. This is especially useful when scanning for variable sources of radiation. The long-standing focus of the RATAN-600's scientific program, however, is the observation of the Sun at radio wavelengths, in particular of the solar corona. The telescope has also contributed to radio observation for the SETI project. (See The Arecibo Observatory).

RATAN-600 was built in 1968 and it started operating in 1974.

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The general plan of RATAN-600: 1 - circular reflector; 2 - a flat reflector; 3 - radial railways; 4 - central receiver; 5 - ring rails.

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The biggest part of the telescope are the rectangular reflecting elements. There are 895 of them and each measures 11 meters in height. Photo credit

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The flat reflector consists of 124 planar elements of height 8.5 meters and a total length of 400 meters. The elements can be rotated about a horizontal axis located near ground level. Photo credit

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The behind of the flat reflectors. Photo credit

The cylindrical reflectors that run on rails. Photo credit

The cylindrical reflectors that run on rails. Photo credit

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The ring rails upon which the flat reflectors rotate. Photo credit

The conical receiver at the center. Photo credit

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Sources: Wikipedia / Russian Wikipedia / Telescopes I've Seen - Bill Keel / IEEE.org