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
Discourse on the Tides is the motion of water relative to the earth, but annual revolution is the motion of the earth, and its water, relative to the sun. Annual revolution results in a force that accelerates the earth-water system but does not accelerate the water relative to the earth, in the same way that an observer standing on Earth's surface does not feel the gravitational attraction of the sun because the observer and Earth are moving together around the sun. The discourse does not include gravitational forces in its theory to explain the Earth's orbit and does not consider the relation between the