Does the Sun affect the tides too?

Yes. The Sun's gravity also pulls on the ocean, but because the Sun is so far away, its pull on the tides is only about half as strong as the Moon's. The Sun matters most when it lines up with the Moon to make spring tides.

Do lakes have tides like the sea?

Lakes have tides too, but they are so tiny you would never notice them. Tides need a very large body of water to be big enough to see, which is why we notice them on the ocean but not in a pond or small lake.

Tides and the Sea | Nature

The sea that comes and goes

If you visit the beach in the morning and then again in the afternoon, something strange may happen. In the morning the sea might be far out, leaving wet sand, shells and rock pools. By the afternoon the water has crept much closer, swallowing the sand where you built a castle. The sea has not gone anywhere — you are watching the tides.

Tides are the slow, daily rise and fall of the sea. When the water comes up the beach, we call it high tide. When it pulls back, we call it low tide. This happens like clockwork all over the world, every single day. But what makes the whole ocean move? The answer lies far above us, in the sky.

The Moon is in charge

The main cause of tides is the Moon, our nearest neighbour in space. Even though the Moon is about 384,000 kilometres away, it pulls on the Earth with an invisible force called gravity — the same force that makes a ball fall when you drop it.

The Moon's gravity is not strong enough to lift the land, but the ocean is liquid, so it can be pulled. The Moon tugs the water on the side of the Earth facing it, making the sea bulge out a little toward the Moon. This bulge is high tide.

Here is a clever part: there is a second high-tide bulge on the opposite side of the Earth at the same time. This happens because the water on the far side is "left behind" as the Earth itself is pulled slightly toward the Moon. So at any moment there are two bulges of high tide, with lower water in between.

Why the tide changes through the day

The Earth spins all the way around once a day. As it spins, each coast passes through the two high-tide bulges and the two low areas in between. That is why most beaches have two high tides and two low tides roughly every day.

The timing shifts a little each day, by about 50 minutes, because the Moon is also slowly orbiting the Earth. That is why high tide is not at the same clock time every day. People who live by the sea use tide tables to know exactly when the water will be high or low.

The water that rises and falls is part of the great ocean that covers most of our planet. You can explore the creatures that live in it in oceans and sea life.

Spring tides and neap tides

Not all tides are the same size. Twice a month we get extra-big tides, and twice a month we get gentler ones. This is because the Sun also pulls on the ocean, though only about half as strongly as the Moon.

Spring tides happen when the Sun, Earth and Moon line up in a straight row, at full moon and new moon. The Sun and Moon then pull together, so their forces add up. This gives very high high tides and very low low tides. (The name has nothing to do with the season spring — it means the water "springs" up high.)
Neap tides happen when the Sun and Moon are at right angles to each other, at the half moons. Their pulls partly cancel out, so the tides are smaller, with less difference between high and low.

So the pattern of the tides follows the Moon's monthly journey around the Earth, like a slow, steady rhythm.

The world the tide uncovers

Tides do more than move water. They create a special place along the shore called the intertidal zone — the strip of beach that is underwater at high tide but uncovered at low tide.

At low tide, this zone reveals a hidden world. Rock pools are left behind, full of crabs, shrimp, small fish, starfish and anemones. The plants and animals here are tough survivors, because they must cope with being underwater half the time and out in the air the other half. Limpets clamp tight to rocks so they do not dry out, and crabs hide under seaweed to stay cool and damp.

The constant push and pull of the tide also shapes the coastline, building up sand on some beaches and slowly wearing away cliffs on others. All this moving water is part of the bigger journey explored in the water cycle.

Why tides matter to people

Tides are not just interesting — they are useful and important.

Fishing and boats. Many harbours can only be entered by boat at high tide, when the water is deep enough.
Safety. Because the tide can rush in quickly and cut off sandbanks or rocks, people must always check tide times before walking far out on a beach.
Clean energy. Some power stations use the huge, dependable movement of the tides to make electricity, called tidal power.
Sea life. Tides bring fresh seawater, oxygen and food to coastal creatures twice a day.

Try it yourself: become a tide tracker

You can observe the tides for real with a simple project.

Find a tide table for a coast near you. These are printed in local newspapers, shown at beaches, and easy to find online. Ask an adult to help.
Choose one week and write down the times of high tide and low tide each day in a notebook.
Look at your list. Can you see the pattern? Notice how the times move later by roughly 50 minutes each day, and how there are usually two highs and two lows.
If you can visit a beach, take a photo from the same spot at high tide and again at low tide. Compare how much the sea has moved.

By keeping your own tide log, you are doing exactly what sailors, fishers and scientists have done for hundreds of years to read the steady rhythm of the sea.

Tides and the Sea

Key takeaways