Source : Webster's Revised Unabridged Dictionary (1913)

   {Pythagorean system} (Astron.), the commonly received system
      of astronomy, first taught by Pythagoras, and afterward
      revived by Copernicus, whence it is also called the
      {Copernican system}.

   {Pythagorean letter}. See {Y.}

Source : WordNet®

Copernican system
     n : Copernicus' astronomical model in which the Earth rotates
         around the sun