Earth's equator is at an angle to the planes of the orbits 4. Time between high tides is 12 hr. The sun has the same effect on tides as the moon, but weaker. The tides that we see at various places on the earth differ somewhat from what you would predict from the above model. Each ocean basin and each coastal area responds uniquely to tidal forces.
Continental barriers interrupt the passage of tides.
Record observed tidal variations 2. Tides are the periodic rise and fall of water level along coastlines. The occurence of tides are related to the phases of the Moon, which was first recognized by Pliny the Elder in the first century. In order to explain tidal periods and inequalities, we consider the effects of tide-raising forces on a model Earth that is entirely covered by oceans. This approach is called the Equilibrium Theory of Tides.