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earth tide
Earth tide or body tide is the displacement of the solid Earth's surface caused by the gravity of the Moon and Sun. Its main component has meter-level amplitude at periods of about 12 hours and longer. The largest body tide constituents are semi-diurnal, but there are also significant diurnal, semi-annual, and fortnightly contributions.
Though the gravitational forcing causing earth tides and ocean tides is the same, the responses are quite different.
==Tide raising force==
The larger of the periodic gravitational forces is from the Moon but that of the Sun is also important.
The images here show lunar tidal force when the Moon appears directly over 30° N (or 30° S). This pattern remains fixed with the red area directed toward (or directly away from) the Moon. Red indicates upward pull, blue downward. If, for example the Moon is directly over 90° W (or 90° E), the red areas are centred on the western northern hemisphere, on upper right. Red up, blue down. If for example the Moon is directly over 90° W (90° E), the centre of the red area is 30° N, 90° W and 30° S, 90° E, and the centre of the bluish band follows the great circle equidistant from those points. At 30° latitude a strong peak occurs once per lunar day, giving a significant diurnal force at that latitude. Along the equator two equally sized peaks (and depressions) are equally sized, giving semi-diurnal force there.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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