Everything you think you know about the tides is wrong (or, at least that's true for me)

Originally published at: Everything you think you know about the tides is wrong (or, at least that's true for me) | Boing Boing


It’s inertia.


The entire first half of the video explains it very well, IMHO.


Yes, and actually I’m withdrawing my “inertia” comment. Evidently that’s a misconception, even among oceanographers.



It’s wild too to think about how the sunset, seemingly ephemeral, is a permanent phenomenon from certain “fixed” vantages.


This wasn’t new new to me, but I did learn about it not that long ago and it is freaky.


That’s your excuse for everything.


This site can help:



The two bulges seem pretty straightforward to me. On the near side, the moon pulls the water more than it does the earth, bringing it up. On the far side, the moon pulls the water less than it does the earth, leaving it behind.

(Edit: note being left behind in an orbit is basically the same thing as the centrifugal force in MikeR’s paper – pull on something less and it ends up further out.)


Reaction GIF by MOODMAN


Unfortunately this explanation requires me to believe the Earth is round.

And the moon exists.

And water is wet.

(OK, that last one is still verifiable, I just checked.)


Do you know how I know that cryptocurrency and NFTs are a scam? Because I can watch a video like this and understand it very well. It makes total sense to me, confirming once again that I am not a moron. I can read about or watch videos on quantum mechanics and understand them. Or relativity. Or speculative papers on how faster than light travel might work. Or wormholes. Or whatever. But I have watched I don’t know how many videos on crypto and NFTs over the past decade or so, some aimed at the 5th grader level and some aimed at grad school level, and I still don’t understand the first damn thing about them or how they work except that they sound like a Ponzi scheme to me.

Anyway, cool video. I think I had learned this before, but forgot it somewhere along the way.


The thing that freaked me out about tides is learning that it doesn’t just affect the oceans. The “solid” ground rises and falls up to 30cm in some places as the planet rotates through the tidal bulges. I was seeing that while working on projects that involved extremely accurate aerial imagery and surveying.


This is very interesting to me. I worked as a surveyor for the USAF many years ago (nothing big or very precise), and still work on GIS applications. I’m curious as to what measurements that would affect and at what scale? Is there somewhere I can read about this?


The Wikipedia article about “Earth Tides” is a decent intro… and the sources in the “References” section ae legit.

The projects I was working on when I learned about the phenomenon were in the late 1990s, early 2000s. We had a project with imagery of Switzerland that was yielding ±10cm vertical/Z-value “errors”/differences while creating highly accurate orthophotomosics using 2cm resolution aerial imagery and high-res LiDAR terrain data… and noticed that the “errors”/differences happened at the edges/boundaries where imagery had been collected on different days a bit more than a week apart… so some of the overlapping imagery showed the same land, but were collected when that land was in different parts of the tidal bulge. We didn’t have the time/resources/budget to fully confirm/calculate how much of the ±10cm vertical/Z-value “errors”/differences were from “Earth Tides” … but the error calcs from other sources, and for the areas with all-same-day collection were significantly lower.

If you want to connect outside of this forum and discuss GIS I’m happy to do that. In fact I’m currently procrastinating on BoingBoing instead of working on my GIS masters project.


Water isn’t wet, it makes things wet.


… but it’s just so much easier than getting up and looking around for another excuse :disappointed:


So… If the moon didn’t orbit the earth, and instead they were just two objects side by side in space, there would only be a water bulge on one side of the Earth, right?

And the height of the bulge would be constantly increasing?

Up until the point where the moon and the Earth collide?

I think I got it!

No. The earth would still be pulled toward the moon more than the water on the far side, and so there would still be a bulge on that side too. In our reference frame it would be described as “inertial” rather than “centrifugal” force but the principle is the same.