The Helmos or 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 and IAASARS.

Its main equipment is the Aristarchos 2.3 m Telescope, manufactured by German company Carl Zeiss AG.

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