Earth tides are caused by the gravitational pull of the moon and the sun on the Earth. The gravitational pull of the moon is stronger than that of the sun, so it has a greater effect on the tides. The gravitational pull of the moon causes the oceans to bulge out in the direction of the moon, creating two high tides and two low tides each day. The gravitational pull of the sun also causes the oceans to bulge out, but in the opposite direction of the moon. This creates two additional high tides and two additional low tides each day. The combination of the gravitational pull of the moon and the sun causes the Earth's tides to change throughout the day.
