The heaving tides are pulled up by gravity from the sun and the moon. The moon pulls harder because it is much closer to us. As our globe spins around every day, it faces the moon with first one side, then another. The moon pulls hardest and drags up a high tide when it is almost overhead. It drags this high tide along as it passes over the sky. This causes a high tide to pile up on the opposite side of the globe and these two high tides are separated by low tides.

Every day, four tides   high and low, high and low, chase each other around the globe. Meantime, once a month the moon orbits the earth. When it gets in line with the sun, the two pull together and our high tides are extra high. Sometimes the moon and the sun pull at the earth from opposite directions and we get lower high tides.