The Science
The Pull of the Moon
Your body is mostly water and the moon moves the sea, so the moon must move you. The tidal force it exerts across your body is about one nanogram — a mosquito on your arm beats it two thousand times over.
The argument is always the same. The moon lifts the ocean. You are sixty per cent water. Therefore the moon lifts you, and on a full moon you should be careful.
Every step of that is wrong, and it is worth knowing exactly how wrong, because the real answer is stranger and better.
The number
What could move anything inside you is not the moon's pull but the difference in its pull between your head and your feet. A uniform pull moves all of you together and moves nothing relative to anything else; you feel it no more than you feel the earth's motion around the sun. The difference is the tidal force, and it is what raises the sea.
It falls off fast. Ordinary gravity weakens with the square of distance; tidal force weakens with the cube, because it is the rate at which gravity itself is changing. That single exponent is the whole story.
About one hundredth of a billionth of a newton. Divide by gravity and you get roughly one nanogram — a billionth of a gram — of extra stretch across your whole body.
A mosquito sitting on your arm exerts about two thousand times more. Not because a mosquito is heavy, but because it is close, and the cube of a small number is a very small number.
Standing up exerts eighteen million times more. Raise your centre of mass by the length of your torso and you move measurably further from the centre of the earth; your own weight changes by about nineteen milligrams. That is a real, computable, utterly unnoticed effect, and it dwarfs the moon.
Then why does the sea do it?
Because the sea is enormous, and because it sloshes.
Tidal force scales with the size of the thing being stretched. The earth's radius is about six and a half million metres; half your height is 0.85. Same moon, same distance — the earth is pulled apart seven and a half million times harder than you are. Tides are a property of the planet's scale. They have nothing to do with water being water.
And even at that scale, the direct effect is modest. If you compute the bulge naively you get well under a metre. Real tides reach many metres in places like the Bay of Fundy because ocean basins are thousands of kilometres across, comparable to the wavelength of the forcing, so the whole basin resonates. It is a bathtub rocked at exactly the right frequency.
Take away the resonance and the tide nearly vanishes. The Great Lakes are vast by any human measure, and NOAA's figure for their spring tide — the biggest, sun and moon pulling together — is less than five centimetres, and even that is drowned by wind and barometric pressure.
If Lake Superior cannot manage two inches, the water in your capillaries is not going anywhere. It is also bounded: there is no basin for it to slosh into, and nothing for it to bulge toward.
And yet the moon does something
Here is where the honest account gets interesting instead of merely dismissive.
There is a real, replicated lunar signal in human sleep. People fall asleep later and sleep less around the full moon — by tens of minutes, not by hours. That is covered properly here, with its sample sizes and its failed replications.
The point for this page is the mechanism, because it is not the mechanism the folklore wants.
For years the answer looked settled: moonlight. In the marine organisms whose monthly clocks are understood best, moonlight is demonstrably the cue. The coral of the Great Barrier Reef spawn on one night a year, together, and they carry cryptochromes — blue-light photoreceptors — whose expression rises on full-moon nights. The bristle worm Platynereis has a circalunar clock that can be reset in a laboratory with nothing but dim artificial light at night, and a photoreceptor protein that physically adopts a different state under moonlight than under sunlight. These animals are not feeling gravity. They are seeing the moon.
Then the picture moved. In January 2026 the same laboratory that produced the strongest field evidence for moonlight posted a reanalysis arguing that the moon's gravitational variation predicts sleep onset better than its illumination does — including in captive titi monkeys, which have little access to natural light. That work is a preprint. It has not been peer reviewed. Its own authors write that it "is observational in nature and based on statistical correlations, which prevents us from drawing causal inferences."
So the mechanism is live and contested, and I am not going to tidy it away in either direction.
The thing worth understanding
If gravity turns out to be involved, it will not be because the moon moves water in you. The ladder above rules that out by twelve orders of magnitude and no amount of new data will rescue it.
It would be because a clock can be set by a signal far too weak to move anything.
That is ordinary in biology. Your circadian rhythm is entrained by light at intensities that do no mechanical work whatever; the light does not push you, it informs you, and a system already oscillating on its own adjusts its phase to match. A periodic cue can be vanishingly faint and still be a superb timekeeper, provided something inside is already keeping time and listening.
The folk claim and the interesting claim are therefore opposites. The folk claim is that the moon is strong enough to move you. The interesting claim is that it is weak enough to be pure information — and that a body might have evolved to read it anyway, on a coastline, a very long time ago.
Which of those is true is not settled. Only the first one is definitely false.