The angular difference between the astronomical axis and the axis of figure called a "nutation" causes an earth orbit al spirical oscillation known as the famous chandler "wobble".
在天文学轴和形状轴之间的角度差称做“章动”，引起地球轨道螺旋摆动，就是著名的卡南德尔“摆动”。
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In this modeling process, the precession, nutation and some other astronomical quantities are considered through two standards released by U. S. Naval Observatory in 1981 and 2005, respectively.