Precession, basically is the change in the direction of earth's axis of rotation.
岁差，基本上是地球自转轴方向的改变。
Concretely, this curl gives you the angular velocity of the rotation, well, with a factor two but that doesn't matter, and the axis of rotation, the direction of the axis of rotation.
它给出了这个旋转的角速率，有一个因子2，但没关系，给出了旋转轴，和旋转轴的方向。
If a torque is applied to the disk in such a fashion that the axis of the torque is the same as that of rotation of the disk, the direction of the former will be parallel to AB.
如果力矩是这样地作用于一圆盘上，即力矩的轴与圆盘的旋转轴方向一致，则力矩的方向与ab线平行。
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