Why are there two tides a day?
There are two tides a day because the tides are caused by the gravitational pull of the moon. This causes the water to build at the point directly under the moon where gravity is highest and at the point on the opposite side of the earth where the gravity attraction is the least. This “wave” then follows the moon as it orbits the earth. Thus shortly after the moon passes overhead the tide comes in and when the moon passes on the opposite side of the earth a second tide comes in. Check Wikipedia for pictures and graphs. http://en.wikipedia.
