歳差運動（軸の歳差）
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<timefyi-glossary slug="precession"></timefyi-glossary>定義
地球の自転軸のゆっくりとしたコマのような首振り運動で、約25,772年で1周する（プラトン年）。歳差運動により、春分点は数千年かけて黄道十二星座を移動する。