1035. How fast does the earth wobble and why does it wobble? — MF, Tokyo, Japan
The earth's rotational axis wobbles around in a circle once every 25,800 years because of torques (twists) exerted on it by the moon's gravity. The moon's gravity is able to twist the earth slightly because the earth isn't quite spherical. The earth's rotation causes it to bulge outward a little around its equator and it is this bulging that allows the moon to exert a torque on the earth.