Rozhen Observatory (Bulgarian: Национална астрономическа обсерватория "Рожен", НАО-Рожен - 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 Southeastern Europe and has an active team of about 50 astronomers.