Rozhen Observatory (also known as NAO-Rozhen) is a Bulgarian astronomical observatory, located 90 km south of the city of Plovdiv, Bulgaria. The nearest town, Chepelare, is 15 km away. It is owned and operated by the Institute of Astronomy of the Bulgarian Academy of Sciences. The Observatory is the largest in South Eastern Europe. Currently there are about 50 astronomers working there. It is recognised as one of the most important centers for astronomical research.