How tidal locking works and Why we see same side of moon always, This moon thing is confusing me very much, I watched many videos and made a understanding but i can’t picture it, too hard for my brain


How tidal locking works and Why we see same side of moon always, This moon thing is confusing me very much, I watched many videos and made a understanding but i can’t picture it, too hard for my brain

In: 1

Tidal locking is the reason that the moon is now “locked” with the earth’s spin. It happens essentially because energy is lost due to “tidal friction” if/when it *doesn’t* spin at the same as it orbits.

The simplest way to think of a tidal lock is that, essentally, many forces slowed down the spin of the moon to the point that it is essentially spinning against its own trajectory.

If you think of it like a bowling ball, the greased lane allows for “back spin” where the ball travels forward, but spins backwards. After a while, this can slow and there is a period where the ball essentially slides on the grease. The back spin has evened out with the friction of the forward travel.

The moon has essentially done this. It is spinning “backwards” along its orbit at the same speed as it is moving forward, essentially “gliding” atop the “oils” of the various forces at play.

Said another way. If you take a ball and tie it to a string, then swing it around your head… While to *you* it seems as if the ball is “always facing you” it is spinning to everyone else. It is just spinning and moving around you at the same time.

The moon still rotates on its axis. Label its hemispheres A and B. Let’s say that right now, A is facing the sun and B is not. In 6 months, B will be facing the sun and A will not. 6 months later, A will be facing the sun again and B will not.

But since the moon’s orbital period is the same as its rotational period, it will orbit the earth in the same amount of time it takes to rotate around its axis once. This is what causes it to present the same face to the earth at all times.

So in the above, when face A is facing the sun, it’s also facing the earth and on the far side (the earth is between them). When face B is facing the sun, face A is still facing the earth, but is now on the near side (between the earth and the sun). It has rotated halfway around its axis and moved halfway around the earth.

As for why, it’s just a natural phenomenon. Energy is lost from the moon’s rotation over time until it slows down enough to become tidally locked. If it were too slow instead, it would be pulled toward the earth while its rotation would be sped up until it became tidally locked. It’s just how gravity acts on objects like this – every moon in our solar system which is large enough to be round (has enough mass to not have irregular shape) is tidally locked to its planet.

Imagine that the moon isn’t tidally locked. As it rotates by, side of the moon facing the earth feels a gravitational pull towards it, and as it rotates away the gravitational pull acts to slow it down just a tiny bit. Over time this “gravitational friction” slows the moons rotation until it becomes tidally locked, where the same face of the moon is always facing earth. This is a stable condition because if a force were to try to change the rotation speed of the moon in either direction, than the gravitational friction will come into play again.

This is a tough one to answer on Reddit, because it needs a diagram. Specifically this diagram:

The Moon is already locked to the Earth. The Earth’s rotation is slowing down as it is still in the process of locking to the Moon. Let’s focus on the Earth, because it’s easier to understand something ongoing and because I couldn’t find a good diagram for lunar locking. 🙂

1) The Moon raises tides on the Earth: a “tidal bulge” is formed in the ocean and also the rock.

2) The Earth’s rotation carries the bulge around so it’s not aligned with the Moon. (See first diagram)

3) The Moon’s gravity pulls harder on the side of Earth that has a bulge closer to the Moon (see second diagram). This means there’s an unbalanced gravity force that tries to slow down the Earth’s rotation, just like you can stop a spinning tire by pushing on one side of it but not the other.

The exact same process happened to the Moon, but because the Earth is so much bigger its tidal effect on the moon was larger and locking happened faster.