Tides
Tides are due to the gravitational attraction of the Moon, and to a lesser extent the Sun, on the Earth. Because the Moon is closer to the Earth than the Sun is to the Earth, it has a larger effect and causes the Earth to bulge toward the moon. At the same time, a bulge occurs on the opposite side of the Earth due to tidal forces. These bulges remain stationary whilst Earth rotates. The tidal bulges result in a rhythmic rise and fall of ocean surface, which is not noticeable to someone on a boat at sea, but is magnified along the coasts.
There are two high tides and two low tides each day, and thus a variation in sea level as the tidal bulge passes through each point on the Earth’s surface. Along most coasts the range is about 2 m, but in narrow inlets tidal currents can be strong and fast and cause variations in sea level up to 15 m.
Because the Sun also exerts a gravitational attraction on the earth, there are also monthly tidal cycles that are controlled by the relative position of the Sun and Moon together. The highest high tides occur when the Sun and the Moon are on the same side of the Earth (new moon) or on opposite sides of the Earth (full moon). The lowest high tides occur when the Sun and the Moon are perpendicular relative to the Earth (quarter moons).
When the Earth, Sun, and Moon are in a line the gravitational pull of the Moon and Sun are combined. At these times, the high tides are very high and the low tides are very low. This is known as a spring tide. Spring tides occur during the full moon and the new moon.
When the gravitational forces of the Moon and the Sun are perpendicular to one another (with respect to the Earth), the Sun and Moon work at right angles, causing the solar and lunar bulges to somewhat cancel each other. The result is a smaller difference between high and low tides. This is known as a neap tide. Neap tides occur during quarter moons.
So there you have it. The Sun and the Moon. Not Neptune at all…