地球轨道偏心率的变化大约在96000年的一个周期内发生。
Changes in the eccentricity of Earth's orbit occur in a cycle of about 96,000 years.
由于偏心率小，我们假定地球绕太阳的轨道和月球绕地球的轨道都是圆形。
Since the eccentricities are small, we can assume that the orbits of the Earth around the Sun and the Moon around the Earth are both circles.
可忽视地球轨道的偏心率，自转，恒星自行和大气折射。
Please disregard the eccentricity of the Earth's orbit, self motions of the stars and all atmospheric effects.
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