TIDESTIDES Where does the water go

when the tide goes out?

Twice every day the sea comes in and goes out along our shores. This movement of water is called tides.

Tides are caused by the gravity of both the moon and the sun “pulling” at the water in the sea. Because the Earth is constantly turning, the “pull” of gravity affects different places as each day goes on - so when the tide is “out” in your area, it is “in” somewhere else.

But the water level at high tide changes too! Why?

Well, we know that the moon orbits the Earth much like the Earth orbits the sun, so the moon and Earth are constantly moving in relation to the sun.

When the moon and sun are in a straight line, like in the first picture below, the pull of gravity is very strong and this causes very high high tides and very low low tides. These very high and low tides are called spring tides.

When the sun and the moon are at right angles to each other, the pull of gravity is not as strong and this causes high tides which are not as high and low tides which are not as low – sometimes there is very little difference between the tide being in and being out! These weaker tides are called neap tides (see the second picture below).

Greater movement

of water

SpringTidesMoon

Earth

Sun

Earth

Moon Sun

Lesser movement

of water

NeapTides

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