Glossary term: 進動
Description: 在天文學中，進動是指天體的自轉軸或軌道參數發生漸變。
天文學中最重要的進動是地軸的進動。由於地球的形狀略微偏離球體，再加上太陽和月球對地球的引力，地球的自轉軸在大約2.6萬年的時間裡劃出一道圓錐形的軌跡。這導致南北天極以及天球坐標系的位置逐漸發生變化。太陽在春分和秋分時的位置也會發生變化，會在黃道帶星系中移動，繞行一週的時間為2.6萬年。
軌道的方向也會發生進動。行星和其他天體圍繞太陽的軌道是橢圓形的。這些橢圓的方向會隨著時間的推移而逐漸改變。最著名的例子就是水星繞太陽軌道的進動。水星軌道的近日點逐漸發生變化，以非常緩慢的速度繞太陽移動，週期為200多萬年。水星軌道以這種方式發生變化的速率並不能通過經典力學的模型很好地解釋。對這一效應的正確建模是愛因斯坦廣義相對論通過的關鍵驗證之一。另一個值得注意的進動是月球繞地球軌道的進動。
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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
This is an automated transliteration of the simplified Chinese translation of this term
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