What Causes the Tides?

Tides are caused mainly by the gravitational pull of the Moon, with the Sun also having a smaller effect. The Moon’s gravity pulls the water in the Earth’s oceans, creating a bulge of water on the side of the Earth facing the Moon.

At the same time, another bulge forms on the opposite side of the Earth. These bulges are where high tides occur, while the areas in between experience low tides.

As the Earth rotates, different places move through these bulges, causing the regular rise and fall of sea levels. Most coastal areas experience two high tides and two low tides each day.

Because the Moon is also moving around the Earth, the timing of high tides shifts slightly, occurring about one hour later each day.