Why Are There Two High Tides and Two Low Tides Every Day?

By Garry Hunt.

The Moon’s effect on Earth can’t be ignored. It’s our closest celestial neighbor and has inspired and intrigued stargazers for as long as there have been human beings to look up at the night sky.

But it also has a very real and tangible effect on the workings of our planet.

Earth’s tides are largely influenced by the gravitational pull of the Moon, or to be more precise, between the gravitational workings of the Sun-Earth-Moon system.

There are two high tides and two low tides per lunar day, but why? What is causing this regularity along Earth’s coastal regions, and what role does the Moon play?

To understand this, we have to think a bit more deeply about the gravitational relationship between Earth and the Moon.

The Moon’s gravitational pull on the oceans is stronger on the side of Earth closest to the Moon than it is on the opposite side.

But there is another force, which is the same everywhere on Earth’s surface, that opposes the Moon’s gravitational pull, called the ‘centripetal force’.

We say that the Moon orbits Earth, but actually they both orbit a point that lies within the Earth.

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