?V.I. Arnold Mathematical Methods of Classical Mechanics SecondEdition Page 50?
Determine the major semi-axis of the ellipse which the center ofthe earth describes around the common center of mass of the earthand the moon. Where is this center of mass, inside the earth oroutside? (The mass of the moon is 1/81 times the mass of theearth.)
NOT JUST 'INSIDE' OR 'OUTSIDE', with specific solution.