What are Spring and Neap Tides?

What are Spring and Neap Tides?

In one lunar month, two Neap and two Spring tides occur. They are a caused by the combined gravitational force of the Moon and Sun which result in bigger than average tides (in the case of a Spring tide), or smaller than average (in the case of a Neap tide).

Sun and Moon Gravitational effect on Spring and Neap tides

What Causes Spring and Neap Tides?

Spring and Neap tides have nothing to do with the seasons. The name Spring comes from the term Springing Forth and refers to the higher than average tide (A Spring tide is also known as a King Tide).

Both Spring and Neap tides are caused by the gravitation pull of the Sun and Moon. This pull is known as the Tidal Force and causes the Earth and its water, to bulge out on the side closest to the Moon and the side farthest from the Moon. When the Sun and the Moon are in alignment, the tidal force is at its strongest which causes a larger bulge of the oceans. This results in a bigger than average tide with a higher high water and a lower low water. These are Spring tides and occur just after a new and full Moon.

Seven days after a spring tide, the Sun and Moon are at right angles to each other. When this happens, the bulge of the ocean caused by the Sun partially cancels out the bulge of the ocean caused by the Moon. This produces moderate tides known as Neap tides, meaning that high tides are a little lower and low tides are a little higher than average. These are Neap tides and occur during a 1st quarter and 3rd quater Moon.

Since the Moon rotates around the Earth in an approximate 28-day cycle, Spring tides occur at two weekly intervals, with a gradual change over a week to a Neap tide.

What is a Tide?

From a sailor’s persepctive, a tide is the the alternate rising and falling of the surface of the ocean that occurs usually twice a day and is the result of differing gravitational forces exerted at different parts of the earth by the Moon and the Sun.

Diagram of neap and spring tide tidal range

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