As long as humanity has been able to see the sky, we’ve had myths and legends about the moon and its powers. One of the more common ones, that pop up every time there’s a supermoon, is that the moon being that close to the Earth is causing natural disasters ranging from earthquakes to tidal waves. But is it really destroying the world? Or is it just poor timing? It turns out the supermoon’s power over the Earth is more in our minds than it is a scientific reality.
To be fair, though, it would seem to follow logically once you know what a supermoon is. The term “supermoon” comes from astrology, but it is a handy term for a perigee syzygy of the Earth, Sun, and Moon. Essentially, the Earth, the Moon, and the Sun are all in a straight line for a short period of time. “Perigee” is simply that the Earth is closest to the Sun, and this happens more often than you might think; going by the astrological definition, there’s a supermoon every fourteen months.
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Anybody who took high school science knows that the tides are affected by the moon, so it would seem logical that the closer the moon is, the more powerful the effect, right? And that’s true, as far as it goes, but not as far as you’d think. It’s absolutely true that the moon and sun have an effect on the ocean tides, thanks to making small changes in the Earth’s gravitational field. And there’s a kernel of truth to the rumor, as the closer the moon is, the greater the effect, resulting in perigean spring tides.
But we’re talking about a matter of inches, not roaring tidal waves. It can still potentially be a problem; perigean spring tides combined with a major storm on Ash Wednesday to cause disastrous flooding up and down the American East Coast in 1962, for example. But it’s not causing tsunamis all by itself.
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As for earthquakes, it would seem reasonable to ask if something like the Moon fiddling with Earth’s gravity might cause something not unlike the Ash Wednesday storm, contributing just enough to a disaster to make it even worse. It’s something seismologists took extremely seriously, not least because it’d be a handy way to anticipate earthquakes and evacuate affected areas, but unfortunately, comparing decades of supermoon and earthquake data hasn’t found any significant correlation.
In short, while the supermoon is pretty, it’s not a sign of the end days or the cause of any natural disasters you hear about. So you can look at those Instagrams without any guilt, at least.
