| 单词 | libration |
| 释义 | libration The phenomenon that enables 59% of the moon's surface to be observed from earth over a 30-year period, in spite of its synchronous rotation. Physical libration arises from slight variations in the rotation of the moon on its axis, caused by minor distortions in its physical shape. Geometric librations are apparent oscillations arising from the fact that the moon is observed from slightly different directions at different times. The geometric libration in longitude results from the nonuniform orbital motion of the moon. The geometric libration in latitude arises because the moon's axis of rotation is not perpendicular to its orbital plane; it enables more of the lunar polar regions to be observed |
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