THE ORBIT AND rotational behavior of the Earth moving about the Sun affects the amount of solar energy received. Precession is the phenomenon where the Earth wobbles about on its axis, just like a spinning top. Consequently, the solstices and equinoxes occur earlier each year. The winter solstice occurs a few weeks before perihelion, the closest approach Earth makes to the Sun. Over time, the summer solstice will occur closer to perihelion and the summer heat will become even greater. This precession of the equinoxes takes 25,800 years to complete. During the period of a precessional cycle, the North Pole follows a circle in space, perpendicular to Earth's imaginary axis of rotation. In concert with the eccentricity of the orbital path around the Sun, and ...