De Sitter 's work was extended in 1918 by Jan Schouten and in 1920 by Adriaan Fokker .
The geodetic effect was first predicted by Willem de Sitter in 1916 , who provided relativistic corrections to the Earth -- Moon system 's motion .
Willem de Sitter   's work was extended in 1918 by Jan Schouten and in 1920 by Adriaan Fokker .
The geodetic effect was first predicted by Willem de Sitter in 1916 , who provided relativistic corrections to the Earth -- Moon system 's motion .