File:Earth orbit.svg

Summary
Considering the Earth-Moon system as a binary planet, their mutual centre of gravity is within the Earth, about 4624 km. from its centre. This centre of gravity has no other physical significance but remains in line towards the moon as the Earth completes its diurnal rotation. It is this mutual centre of gravity which defines the path of the Eath-Moon system in solar orbit. Consequently the Earth's centre veers inside and outside the orbital path during each synodic month. Geologician (talk) 22:41, 24 June 2009 (UTC)