Every time the moon completed one orbit, its closest approach to Earth would shift by about a trillionth of a degree, or about half a millimeter.

• 这个运动大到几乎可以在关于月球距离的实验中观测到，该实验是利用阿波罗太空人放在月球上的镜子，反射雷射光以监测月球轨道。