The Structure of the Earth: Rotation, Precession, Cosmogony
摘要
Our planet rotates once a day on its axis. The rate of this rotation—the exact duration of a day, i.e., the time between two successive sunrises—is not perfectly constant; it varies a little, and very slowly, over time; and the same is true of the direction of the rotation axis—which changes, also very slightly, kind of like the axis of a spinning top.