Why do oceans have tides?

The Moon pulls unevenly

The Moon’s gravity is slightly stronger on the side of Earth facing it and slightly weaker on the far side. This difference creates tidal forces that deform the ocean and the solid Earth. The effect is about the gradient in gravity, not simply the Moon’s total pull.

Earth’s rotation and the Moon’s orbit determine how a coastline moves through the resulting pattern. Real oceans do not form two perfect water bulges around a smooth planet.

The Sun can reinforce or reduce tides

When the Sun, Earth and Moon align near a new or full Moon, their tidal effects combine and produce spring tides with a larger range. At first and third quarter, the forces partly offset and neap tides have a smaller range.

These names describe tidal range, not the season of spring. Local geography can make the difference more or less noticeable.

Why every coast has its own schedule

Continents, bays, seafloor depth and resonance shape the tide. Some locations have two high tides each day, some have one, and others show mixed patterns. Weather and air pressure can add temporary water-level changes.

A tide table is therefore location-specific. The Moon supplies the main rhythm, but the coastline determines how that rhythm appears at the shore.

The solid Earth also rises and falls

Tides are not only an ocean event. The ground beneath a coastline moves slightly under the same gravitational forcing, and ocean basins respond according to their shape. Tide gauges measure the combined change in sea level and land motion, which is why careful coastal measurements need a stable reference.