sentences:  It owns and operates the Bulgarian National Rozhen Observatory located at an altitude of 1750 m in the Rhodopi mountains in south-east Bulgaria, as well as the Belogradchik Observatory situated at 650 m at the foot of the Western Balkan Mountains in north-west Bulgaria.The institute was inaugurated in 1958 as an independent section of the larger Institute of Physics of the Bulgarian Academy of Sciences by the academician Nikola Bonev.In 1995, it became a separate institute.