What Are Ocean Tides Caused By?
The Earth and the Moon As the Earth exerts gravitational force upon the moon, so does the moon’s gravity affect the Earth. Although relatively weak by comparison, the force of the moon’s pull is sufficient to influence sea levels; thus, the ocean bulges on the side of the Earth facing the moon. As the Earth rotates through this bulge, it experiences a high tide. If the moon’s pull upon the Earth were the only factor affecting tides, then our planet would experience only one high tide and one low tide per day. In fact, Earth experiences two of each, called semidiurnal tides. Why? The moon does not simply revolve around an unmoving Earth. In fact, the Earth and the moon share a single center of gravity, or barycenter, located 1,068 miles down from the surface of our planet. At this point, the greatly differing masses of the Earth and the Moon are balanced: the Earth does not collide with the Moon, nor is the Moon simply flung out into space. As the two bodies spin around this mutual poin
