PREVIOUS PAGE
TIDES are the regular RISING and FALLING of the sea. You will have seen this if you have ever been to the SEASIDE. When it is HIGH tide, the water has come a long way up the beach and at LOW tide you will see lots of the shore because the sea has gone a long way out. There are about TWO High tides and TWO low tides a DAY.
Tides are due to the GRAVITY of the MOON trying to PULL upwards the sea which is nearest to it. In the diagram below, there will be a HIGH tide at POINT A on the Earth because of this pulling effect. There will also be a HIGH tide on the opposite side of the Earth at POINT C, while at POINTS B and D there will be a LOW tide.
The Earth ROTATES once every 24 hours which means that the PLACES on the Earth where HIGH and LOW tides are changing. The diagram below shows where HIGH and LOW tides will be 6 hours after the diagram above.
The SUN also has a PULLING effect on the sea. Although the Sun is LARGER than the Moon it is FURTHER away from the Earth which means that it has LESS effect on our TIDES than the Moon.
TWICE a MONTH the Moon AND the Sun are in line with the Earth and so they PULL together. This causes VERY HIGH and VERY LOW tides called SPRING tides.
TWICE a MONTH, about half way between Spring tides, the Sun and Moon are at RIGHT ANGLES to each other and so their TWO PULLS are not as great. This causes much smaller tides. These are called NEAP tides.
