Alex McColgan

Join with me today as we learn about the innocently named Lunar Nodal Cycle and why we need to start developing a much better understanding of the fluctuating behaviour of our Moon if we are to protect ourselves against its dangers.

Much like the Sun, the Moon is an inescapable part of life on Earth.

The Moon has an immense impact on our planet.

You likely have already heard how its cycles influence our wildlife, affect our climate, and create tides.

We tend to imagine that the Moon and the Earth's gravities cause them to circle each other in a relatively stable, synchronised harmony.

As is so often the case, nature is not as simple as we imagine it.

Instead, every 18.6 years, the moon's orbit undergoes a subtle revolution.

A shift in its alignment between us and our sun that causes high tides to grow even higher, tipping us over the edge into dangerous flood territory.

But let's delve into what this subtle revolution is.

Its name is the Lunar Nodal Cycle, or the Procession of Lunar Nodes.

This complex name refers to a specific feature of the Moon's orbit of the Earth.

You likely know that every 29.5 days, the Moon orbits the Earth.

However, this orbit is not flat, or to be more specific, there is a 5 degree difference between the angle of the Moon's orbit and the ecliptic plane, the 2D plane on which the Earth orbits around the Sun.

For half of the month, the Moon is slightly higher than the plane of the ecliptic.

For the other half, it drops below it.

Naturally, this means that there are two crossover points, or two nodes – an ascending node and a descending node – that mark the point where the moon goes from one side over to the other.

And it is these nodes that move over the course of the 18.6 year cycle, slowly rotating around the planet in one complete revolution.

The nodes themselves are what causes the problem.

To understand why, let's recap what we know about tides.

You may already be familiar with how the moon's gravity pulls the Earth's water towards it, causing a bulge in sea levels on the side closest to it that we call high tide.