Also called precession of the equinoxes, this component (the other two being eccentricity and obliquity) of the orbital perturbations that comprise the Milankovitch theory is actually two components. The first is axial precession, where the earth's axis of rotation wobbles likes a spinning top due to the torque of the sun and the planets on the non-spherical earth. Therefore the North Pole describes a circle in space with a period of 26,000 years. The second is elliptical precession in which the ellipse that is the earth's orbit is rotating about one axis. Both effects combined are known as the "precession of the equinoxes" where the equinox (March 20 and September 22) and solstice (June 21 and December 21) shift slowly around the earth's orbit with a period of 22,000 years. The eccentricity modulates and splits the precession frequency into periods of 19,000 and 23,000 years. The precession causes warm winters and cool summers in one hemisphere and the opposite in the other, with the effect being largest at the equator and diminishing towards the poles.