With respect to an inertial frame of reference I guess. (A frame rotating relative to an inertial frame is not an inertial frame anymore.) Edit: No, I was wron

With respect to an inertial frame of reference I guess. (A frame rotating relative to an inertial frame is not an inertial frame anymore.) Edit: No, I was wrong. It wobbles with respect to someone viewing it from the the earth looking towards the moon. (Which is not an inertial frame of reference.)