Glossary term: 进动
Description: 在天文学中，进动是指天体的自转轴或轨道参数发生渐变。
天文学中最重要的进动是地轴的进动。由于地球的形状略微偏离球体，再加上太阳和月球对地球的引力，地球的自转轴在大约2.6万年的时间里划出一道圆锥形的轨迹。这导致南北天极以及天球坐标系的位置逐渐发生变化。太阳在春分和秋分时的位置也会发生变化，会在黄道带星系中移动，绕行一周的时间为2.6万年。
轨道的方向也会发生进动。行星和其他天体围绕太阳的轨道是椭圆形的。这些椭圆的方向会随着时间的推移而逐渐改变。最著名的例子就是水星绕太阳轨道的进动。水星轨道的近日点逐渐发生变化，以非常缓慢的速度绕太阳移动，周期为200多万年。水星轨道以这种方式发生变化的速率并不能通过经典力学的模型很好地解释。对这一效应的正确建模是爱因斯坦广义相对论通过的关键验证之一。另一个值得注意的进动是月球绕地球轨道的进动。
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Term and definition status: The original definition of this term in English have been approved by a research astronomer and a teacher The translation of this term and its definition is still awaiting approval
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