Tides are great bulges of water on the surface of the oceans caused by the gravitational forces of the Moon and the Sun. Gravity is that force which keeps you on the Earth and stops you from floating off. It also keeps the Earth and other celestial bodies, like the Sun and the Moon, in their orbit.

When the gravity of the Moon pulls on the Earth, it causes a bulge on the surface of the oceans as it pulls the water slightly towards it. The mound of water rises and when it reaches its highest point it is called a high tide. Another high tide occurs on the opposite side of the Earth, since the Earth is also being pulled towards the moon and away from the water on the far side. As the Earth rotates, the force of the moon keeps mounding the water and that water moves around the planet.

When the level of the water falls, there is a low tide. In some places on Earth one high tide and one low tide occur each day, in other places two high tides and two low tides occur.

Even the sun exerts gravitational forces on the Earth, but its effect is less than half that of the Moon. But when the Sun and the Moon are aligned and pull in the same direction they cause higher high tides and lower low tides called “spring tides”. When the Sun and Moon are at right angles to one another, with the moon pulling in one direction and the sun pulling in another, you get lower high tides and higher low tides called neap tides.

The difference between the high tide and the low tide is called the range of the tide. The range can vary from a fraction of a metre to several metres. The greatest tides recorded had a range which exceeded 15 metres!

The first person to provide a scientific explanation of tides was Isaac Newton.

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