How do you calculate the tides?

How do they calculate oceanic tides in different places?

• Answer:

  Oceanic tides are caused by the gravitational attraction of the moon which raises up the ocean water beneath the moon causing a high tide. On the opposite side of the earth there is another high tide bulge caused in part by the spin of the earth. On the coast we observe two high and two low tides each day. As the earth spins the tidal bulge approaches a coast. The shape of the coast affects the height of the tide. At the Bay of Fundy in eastern Canada, the tide can equal about 45 feet at times because the tide is pulled into a converging channel that amplifies the tide. On other coasts, for example Caribbean islands, there is very little tide. Because the gravitational force of the sun also produces a lesser tide than the moon, the sun and moon work together or against each other in a complex way to vary the height of tides as the earth rotates about the sun in a less than perfect circle and the moon rotates about the earth and the earth spins on its axis. The angle of the earth's axis relative to the sun changes with the seasons also affecting heights of tides below the sun. Therefore at selected coastal stations, the tides are measured over long periods ot time in special hollow tubes with measuring scales (that are not affected by waves) and statistics are collected to predict future tides relative to the positions of the sun and moon. These data can be extrapolated or interpolated to prepare tide tables for nearby coastal areas that do not have their own measuring tubes.