Tidal Energy

Tides on a Global Scale: Tidal Bulges

Due to the Moon's gravitational pull, tidal bulges develop. The tidal bulges move as the Earth rotates and the Moon changes position relative to the Earth.

The part of the Earth closer to the Moon is more strongly attracted to the Moon than the part farther from the Moon which is less strongly attracted. So, the close part gets closer and the far part gets farther. This makes the elongation in both directions that we observe in the illustration above. It also causes there to be two high and low tides each day for most of the oceans of the world.

Since the Earth rotates a full turn every day, the point on the Earth that is being pulled toward the moon is constantly changing. As the angle changes between the Moon and the Equator, the tidal bulges change position on the Earth. Most places on Earth have two high tides and two lows every day because of the Earth's rotation and the Moon's change of position.