The moon has a noticeable effect on the earth in the form of tides, but it also affects the motion and orbit of the earth. The moon does not orbit the center of the earth, rather, they both revolve around the center of their masses called the barycenter. The sun acts on the earth and its moon as one entity with its center at the barycenter. Since the earth revolves around the barycenter, which in turn orbits the sun, the earth follows a wobbly path around the sun. To complicate things further, the barycenter is not always in the same place due to the elliptical nature of the moon's orbit. The moon also changes the position of the earth's equinoxes. The sun and moon each attract the earth's equatorial bulge, trying to bring it into alignment with themselves. This torque is counteracted by the rotation of the earth. The combination of these two forces is a slow rotation of the earth's axis, which in turn results in a slow westward rotation of the equinoxes.