Earth tide Earth tide Earth tide (also known as solid Earth tide, crustal tide, body tide, bodily tide or land 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. The larger of the periodic gravitational forces is from the Moon but that of the
Chinese sun and moon mirrors moon-mirrors and beliefs that certain marine animals waxed and waned in correspondence with the moon. For example, the (c. 3rd century BCE) "Guanzi" says, The virtue of a ruler is what all the people obey, just as the moon is the root and fount of all Yin things. So at full moon, shellfish ["bangge" 蚌蛤] are fleshy, and all that is Yin abounds. When the moon has waned, the shellfish are empty and Yin things weak. When the moon appears in the heavens all Yin things are influenced right down to the depths of the sea. So the sage lets