Tides are long-period waves that move through the ocean in response to the gravitational pull of the Moon and the Sun. The Moon tugs on the entire Earth, not only on the water in front of it, so the ocean ends up a little higher on the side facing the Moon and a little higher on the side facing away. As the planet turns beneath those two bulges, most coastlines pass through both of them in a day, which is why the water rises and falls twice. The gap between high and low water is called the tidal range. For the full definition, see oceanservice.noaa.gov.
Why the ocean bulges on both sides
It looks strange that water on the far side of the planet also rises. The pull is strongest at the points closest to the Moon and weakest at the points farthest away, but every drop of water feels it, because gravity acts on the whole planet. The ocean is not lifted straight up. It is pushed and squeezed sideways, until it settles into a slightly oval shape that is elongated towards the Moon and away from it. The solid Earth responds too, though so faintly that instruments rather than eyes are needed to detect it. NASA’s overview of tides, at science.nasa.gov, describes both effects.
Why the next high tide is about 50 minutes later
A high tide to high tide cycle runs a little over 12 hours, so a coastline usually gets two highs and two lows in a day. The extra time comes from the Moon itself. Because the Moon orbits in the same direction the Earth spins, a given spot has to rotate a little further to catch up with the bulge. That is roughly 50 minutes of extra turn each day. The practical result is that tides drift later through the day instead of holding a fixed clock time, and the highest water sits slightly ahead of the Moon rather than directly under it.
What the Sun adds: spring and neap tides
The Sun is enormous but distant. According to NASA, it holds about 27 million times the mass of the Moon yet sits roughly 390 times farther away, which leaves it with a little less than half of the Moon’s tide generating force. Twice a month, at new and full moon, the Sun, Earth and Moon line up and the two pulls add together, producing the larger ranges known as spring tides. About seven days later the Sun and Moon sit at right angles, so the pulls partly cancel and the milder neap tides follow. The name spring has nothing to do with the season; it refers to the tide springing forth, as NOAA’s explainer on spring and neap tides sets out.
Why two nearby coasts can behave differently
On a smooth planet with no continents, every shore would see two even high tides a day. Continents block the westward passage of the bulges as the Earth rotates, so each ocean basin develops its own rhythm. NOAA’s tidal cycles tutorial at oceanservice.noaa.gov lists three common patterns: semidiurnal, with two highs and two lows of similar height; mixed semidiurnal, with two highs and lows of differing heights; and diurnal, with a single high and a single low each day. Parts of the Gulf of Mexico are diurnal, the U.S. West Coast tends to be mixed, and the East Coast is more typically semidiurnal. Wind, storms and the shape of a bay layer further variation on top of that astronomy.
How to use this in practice
The astronomy sets the rhythm, but it does not set the exact height at your beach. Local tide predictions combine the positions of the Moon and the Sun with shoreline shape and historical water level observations. If you are planning a walk, a swim or a boat trip, the local forecast is the figure to trust, not a rule of thumb based on the Moon alone.
Bottom line: The Moon does most of the work and the Sun adjusts it. Two bulges, a drift of about 50 minutes each day, wider ranges around new and full moon, and coastlines that shape the rest. That is the whole tide story in one paragraph.