Theories of tidal action

Although the Sun is larger than the Moon, the Moon is closer to
Earth and, therefore, has a greater influence on Earth’s ocean tides. The
Moon’s gravity pulls on the ocean water on the near side of Earth. This
force causes the water, since it is able to flow, to form a slight bulge outward,
making the water in that area slightly deeper.
At the same time, on the opposing side of Earth, a second tidal bulge
occurs that is the same size as the first. This second bulge forms because
the force of the Moon’s gravity pulls the solid body of Earth away from
the water on Earth’s far side. The result is that two lunar tidal bulges exist
on Earth at all times—one on the side of Earth facing the Moon and
another directly opposite to it. These bulges account for the phenomenon
known as high tide.

The formation of these two high tide bulges causes a belt of low
water to form at 90-degree angles to the high tide bulges. This belt, which
completely encircles Earth, produces the phenomenon known as low tide.
In addition to the lunar bulges, the Sun forms its own tidal bulges.
However, due to the Sun’s much greater distance from Earth, its tidal effect
is approximately one-half that of the Moon.
Every 14 days, the Moon and Sun are in line with each other (new
moon and full moon). Their gravitational forces combine to produce a
maximum pull on Earth. The tides produced in such cases are known as
spring tides. The spring high tide produces the highest high tide and the
spring low tide produces the lowest low tide.