Why do tides occur

Ocean tides can be described as the rise and fall of sea-water in a cyclical fashion. The tides themselves are as a result of variations in the gravitational pull (or attraction) between the Earth, the Moon and the Sun. These occur in a geometric relationship with places located on the surface of the Earth. Tides are periodic as a general result of the fact the the Earth has a cyclical rotation.

The main controlling factor with regard to both the height and rhythm of the Earth’s tides is the Moon. Through the general effect of its gravitational pull the moon causes two continuous tidal bulges at some point on the Earth. The height of the tidal bulges is overseen by the upward gravitational force of the Moon, coupled with the Earth’s gravitational pull which pulls the water back down. In the case of the places on the earth that are closest to the Moon the oceans there are pulled towards the Moon as a result of the Moon’s greater gravitational pull and attraction on them due to proximity. On the Earth’s opposite side, there is another tidal bulge away from the Moon. The opposite bulge is as a result of it occurring at the point where the Moon’s gravitational attraction (pull) is at its weakest.

As a result of these influences any point on the Earth would have two high tides at any given time – also known as crests – and two low tides – known as troughs – during every tidal period. The actual timing of the tides themselves is as a result of both the rotation of the Earth and where exactly around the Earth the Moon sits at any given time. If, for instance, the Moon ceased to orbit there would be a perfect 24-hour daily cycle on Earth. The complete lunar cycle means that it takes 27 days to revolve around the Earth, adding approximately 50 minutes to its cycle, which results in a tidal period of 24 hours and 50 minutes.

Apart from the Moon the Sun also contributes to our tides, with the average solar tide being roughly half that of the lunar equivalent. At the point where the direction of the Moon’s gravitational pull aligns with that of the Sun these two attractions act in concert to produce both the highest and lowest tides of the year. These are Spring tides, and we see them roughly every two weeks during new and full moons.

There are also Neap Tides, and these occur when the pull of the Sun and the Moon are at right angles to each other. At this point, daily variations in tides are at their lowest point on Earth. While Neap Tides are uncommon compared to regular tidal currents and changes they are still particularly interesting occurrences and, if not handled appropriately, can cause some very difficult times for many boats and other areas near these in order to adapt for the temporary tide reduction should it be a major low point.