The Tides

Tides are the cycle of the Earth's rising and falling ocean surface.  This is caused by the tidal forces of both the sun and moon acting upon the earth.  The tides cause drastic changes in depth throughout the sea.  They also produce oscillating currents which are also known as tidal streams.  Making prediction of the tides is essential 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 tides produced at a specific location on earth is the result of the Moon and Sun interacting with the Earth. "Though the gravitational force exerted by the Sun on the Earth is almost 200 times stronger than that exerted by the Moon, the tidal force produced by the Moon is about twice as strong as that produced by the Sun."  This is because the tidal force isn't necessarily related by the strength of a gravitational, but to its incline.  The field incline decreases with distance from the source more quickly than does the field strength.  The Sun is roughly 400 times further from the Earth than the Moon is.   The gradient of the Sun's field, along with the tidal force made by the sun is more weak than the Moon's. 
  
website:  http://www.sciencedaily.com/articles/t/tide.htm
picture:  http://www.greenlaunches.com/wp-content/uploads/2013/01/ocean_tides.jpg