The Chelmos Observatory (Greek: Αστεροσκοπείο Χελμού) is an observatory located at the top of mount Chelmos, near Kalavryta, southern Greece. It is the largest research infrastructure of the National Observatory of Athens. The observatory was completed and first opened in 2001. Its main equipment is the Aristarchos 2.3 m Telescope, manufactured by German company Carl Zeiss AG.