(Enchanted Learning, 2008). The ability to accurately predict tides has a variety of important implications, including coastal navigation. (Wikipedia, 2008). Because tides have such important implications, it is important and useful to examine the processes by which changing tides occur.
There are two high tides and two low tides every day, with about "12 hours and 25 minutes between the two high tides." (Cooley, 2002). The exact time the high tide occurs depends on the relative location of the moon to earth. The distance between the earth and the moon is a crucial factor in determining tides and tidal range. Two words that are helpful to understand in examining the distance between the earth and moon are "perigee" and "apogee." When the moon is at perigee, or its closest to the earth, the tidal range is increased. When the moon is at apogee, or its farthest distance from the earth, this range is decreased. (Whipple, 2007 & Wikipedia, 2008).
The reason that the distance of the earth from the moon has such a profound effect on tidal range is because of gravitational pull. Although the mass of the moon is much less than the mass of the earth, the moon still pulls the earth towards it by means of its gravity. This gravitational pull causes two bulges in the surface of the ocean on opposite sides of the earth, and the spinning of the earth on its axis creates tides as the bulges change location. (Frances, 2005). Because water is always in motion and isn't stuck to the earth, water on the earth is most affected by the moon's gravitational pull. On the side of the earth that is near the moon, water is pulled toward the moon, but on the other side of the earth, there is also a bulge of water. This is because the earth as a whole is being pulled toward the moon by the side that is close to the moon but the water on the other side of the earth is not. (Cooley, 2002).
One type of tide is called a spring tide. A spring tide refers to the occurrence of the greatest range in a tide's low and high. In other words, during this tide there will be the greatest distance between how high the water gets and how low the water gets. This happens when there is a syzygy. A syzygy refers to the lining up of the sun, earth, and moon. (Wikipedia, 2008). The reason that the tidal range is greatest during a spring tide is because the gravitational pull of the sun and moon combine to produce the highest highs and lowest lows of the bulging water. (Cooley, 2002). It is also interesting to note that Spring tides occur around the time of new and full moons. (Wikipedia, 2008). When there is a new moon, the moon is in between the sun and the earth. When there is a full moon, the
The Proxigean Spring Tide is an especially high tidal range that occurs once about every one and a half years. It happens when the moon is new and is at proxigee. Proxigee refers to when the moon is at its closest perigee to earth. (Cooley, 2002).
The opposite of a spring tide is a neap tide. A neap tide refers to the occurrence of the smallest range in a tide's low and high. Neap tides occur when th