The Special Astrophysical Observatory (Russian: Специальная Астрофизическая Обсерватория), or SAO RAS for short, is an astronomical observatory, set up in 1966 in the USSR, now operated by the Russian Academy of Sciences. Based in the Bolshoi Zelenchuk Valley of the Greater Caucasus near the village of Nizhny Arkhyz, the observatory houses the large BTA-6 optical telescope and RATAN-600 radio telescope.