The angular difference between the astronomical axis and the axisof 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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Based on the character of off-axis and multi-pass amplification systems, the possibilities are analyzed that some part of the line could form optical oscillator and occur self-excitation oscillation.