Figure 2: Galileo′s observation records of Jupiter’s moons from January 7, 1610, through January 13, 1610. Initially, Galileo’s presumed that the three or four little stars (depicted by the symbol *) around Jupiter (depicted by the symbol O) to be fixed stars. He thought he was monitoring the apparent trajectory of Jupiter relative to the background of these fixed stars. The designations of direct motion and retrograde motion were Galileo’s interpretations under this unproven assumption. See text for further detail. (Reproduced and modified from [83]).