The Special Astrophysical Observatory (SAO) of the Russian Academy of Sciences is located east of the Black Sea in Russia.
It lies near the village of Zelenchukskaya, on the northern slope of the Caucasus Mountains. Two notable instruments are at the site. One is the 6-m (236-in) optical reflector completed in 1976 atop 2,100-m (6,900-ft) Mount Semirodniki. It is called the BTAÑan acronym from Russian words meaning Big Azimuth TelescopeÑbecause of its novel computer-controlled altazimuth mounting. A conventional equatorial mounting would have been too large to enable accurate observations.The other notable
instrument at SAO is a radio
Telescope called RATAN-600, an acronym from Russian words for Radio Astronomy Telescope of the Academy of Sciences. Located 20 km (12 mi) northeast of the BTA, its ring-shaped primary reflector is 576 m (1,890 ft) in diameter. The 895 panels of the reflector provide a total collecting area of about 13,000 m6 (139,931 ft6). The RATAN-600 is used for studying radio galaxies, extragalactic nebulae, and interstellar clouds of neutral and ionized hydrogen and hydroxyl. The instrument can also be employed for radiolocating and communicating with space probes in remote parts of the solar system.