Lunar Tides

Tides are basically the rise and fall of the sea surface relative to land. They are basically produced by gravitational forces from the Sun and the Moon. Two major lunar tide types are Spring Tide and Neap Tides. The NAOO has a nice little diagram of how both occur. Spring tides occur when the moon is full/new and the gravitational pull of the sun are combined. Neap tides occur when the moon and sun are at right angles of each other. The end result is that Spring tides have higher highs and lower lows and neap tides are less intense tides. Check out this site for more information.