Tides

Physicists have derived precise mathematical expressions to describe the gravitational effects of the Moon and the Sun on the Earth. In theory, therefore, it should be possible to make precise predictions of the timing and sizes of all of ocean tides. In fact, absolutely precise predictions Low tide at Big Pine Key, Florida. JLM Visuals. Reproduced by permission. are not possible because a large number of factors contribute to the tides at a particular location. Primary among these is that the shape of ocean basins is so irregular that the water in them cannot behave in a simple way. Other variables also complicate the situation. These include variations in the Earth's axial rotation and variations in Earth-Moon-Sun positioning, including variations in orbital distance and inclination. Estimates of tidal behavior are therefore still based primarily on previous tidal observations, continuous monitoring of coastal water levels, and astronomical tables. (Comparison of predicted with measured tides along U.S. coasts can be checked at <http://tidesonline.nos.noaa.gov/>, a Website maintained by the U.S. government.)