You will have heard of the expression ‘spring tide’ or ‘neap tide’, but do you know what it is or what causes it? Here’s an explanation.
Ste Wright | 2 min read
Our tides are controlled by the gravitational pull of the moon as it orbits Earth. There are two extremes of the tide; spring tide (or sometimes referred to as ‘King’ tide) and neap tide. Spring tide essentially is the two tides where the sea is at its most extreme; the highest and lowest. In contrast, a neap tide is one where the difference between the high and low tides is at its lowest.
The spring tide is where the sun and the moon align to create the greatest gravitational pull on the sea. This is because both the sun and the moon have combined greater gravitational force which pulls the sea towards them. This means the side of the earth where both the sun and the moon align have the lowest tide, where the opposite side of the earth experiences the highest.
Not to scale. The diagram above shows the moon’s rotation around the earth (red), the Earth’s rotation around the sun (yellow). When the sun and the moon’s gravitational forces combine, they create the greatest tidal bulge (dark blue).
When the sun and moons are at right angles to each other, there is least gravitational pull, meaning the tidal range is at its lowest. The neap tide occurs 7 days after the spring tide.
Not to scale. The diagram above shows yet again, the moon’s rotation around the earth (red), the Earth’s rotation around the sun (yellow). When the sun and the moon’s gravitational forces are at right angles to each other, they create the least tidal bulge.