因为地球自转，它被太阳照亮的一侧是是白天，而处在黑暗中的一侧是夜晚。
As the earth rotates, its side that is lighted by the sun is day time, while its side that is in darkness is night time.
近地半球总是面对地球，远地半球总是远离地球，因为月球在绕地球旋转的同时，它也在以同样的速率绕自己的轴自转。
The near side is always facing Earth and the far side is always facing away, because the moon revolves around the Earth at the same rate that it rotates on its own axis.
地球的自转角度能够保持不变，完全是因为有了月球的引力拉动。
The Angle of earth's spin is constant only because the moon's gravitational pull.
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