: how does the moon affect the ocean tides despite being so far away? and what aspect of the ocean does the moon affect?
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The moon is far away but it’s still large enough to effect gravity. as it circles the earth it’s pulling on the earth but not enough to effect the earth itself because it’s much smaller in mass, it does however pull the water and in doing so it effects the direction of the tides.
Short answer: Gravity. Just like the Earths gravity pulls the Moon toward it, the Moon also pulls on the Earth, though not quite as strong, because it’s a lot smaller than Earth. In fact, you were probably taught in school that the Moon orbits the Earth, but technically, they both orbit a point inbetween them called a barycenter, but i digress.
See, when the Moons gravity pulls on things on Earth, it pulls on every particle individually, thus making all of them want to move towards the Moon. For the crust, this isn’t really an option, as the Earths gravity along with intermolecular forces keep it in place (Though it does deform a little bit), but the same is not true for the oceans.
Since they are liquid, the particles in the ocean can move freely, more or less. Thus, you’ll have some particles within the water bunching up in the side that is turned towards the Moon, and this mountain of particles “follows” the Moon as the Earth turns, which is why tides exist.
The force of gravity goes down as distance increases. Therefore, the strength of the moon’s gravity on the part of the Earth closest to the moon is slightly higher than it is on the part of the Earth furthest from it. If you imagine the whole Earth and look at how the Moon’s gravity affects each part of it, then subtract from that the average gravitational pull of the moon, what you’re left with is tidal gravity. This results in a kind of squeezing effect, which this image does a good job of depicting: [https://www.lockhaven.edu/~dsimanek/scenario/stress.gif](https://www.lockhaven.edu/~dsimanek/scenario/stress.gif)
This effect when it comes to the Earth and Moon is very small, but because the oceans are large and fluid, they are affected by this, causing high tides on the parts of the Earth along the line joining its center with the Moon, and low tides on a plane perpendicular to that.
The Earth rotates of course, and friction causes it to kind of drag the tides along with that rotation, and this is the one of the major reasons why Earth’s rotation is slowing. The moon is constantly trying to pull those tides back along that friction, slowing the Earth. Conversely, because of the tides being dragged ahead by the rotation, it actually slightly shifts the Earth’s center of mass enough to pull the moon into higher orbit. Essentially, the Moon is stealing Earth’s rotational inertia, slowing its rotation and expanding its own orbit, via tides.
The sun also has a similar effect on Earth with regards to the tides, but despite the Sun pulling harder on the Earth than the Moon does, the effect is smaller. It’s less about the total magnitude of the gravitational force, and more about how much it changes over the width of the Earth. Due to Earth’s much greater distance from the sun, the difference in gravitational force between the closest and furthest points is much smaller, and so the tidal effect is smaller. But it is there, and that is the thing responsible for there being spring tides and neap tides, based on how much it aligns with or conflicts with the Moon’s tidal effects as the Moon orbits the Earth.
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