Monday, January 7, 2008


Tides are the rising and falling of Earth's ocean surface caused by the tidal forces of the Moon and the Sun acting on the oceans. Tidal phenomena can occur in any object that is subjected to a gravitational field that varies in time and space, such as the Earth's land masses.
Tides noticeably affect the depth of marine and estuarine water bodies and produce oscillating currents known as tidal streams, making prediction of tides very important for coastal navigation. The strip of seashore that is submerged at high tide and exposed at low tide, the intertidal zone, is an important ecological product of ocean tides.

The changing tide produced at a given location is the result of the changing positions of the Moon and Sun relative to the Earth coupled with the effects of Earth rotation and the local shape of the sea floor. Heights and times of low and high tide on each day are published in tide tables. The actual depth of water at the given points at high or low water can easily be calculated by adding the charted depth to the published height of the tide. The tidal range is the vertical difference between the highest high tide and the lowest low tide. In other words, it is the difference in height between high and low tides. The most extreme tidal range will occur around the time of the full or new moons, when gravity of both the Sun and Moon are pulling the same way (new moon), or exact opposite way (full). This type of tide is known as a spring tide. During nea tides, when the Moon and Sun's vectors make a right angle at the Earth, the difference between high and low tides is smaller. Neap tides occur during the firsts and lasts quarter moons.