Why is it that Moon moving away from us and earth’s rotation slowing down?
Have you ever thought that what will happen if the moon goes away from earth or the earth stop rotating?
There are many theories that say the moon is going away from us and what will happen if that happens. Seeing these theories we can get an idea of what will happen if the earth stops its rotation or moon goes away. When Neil Armstrong and Buzz Aldrin landed on the moon, they left behind a mirror. With this mirror, we can reflect laser beams off the moon. And this lets us measure the distance to the moon.
We’ve discovered that the moon is slowly drifting away from us. It’s drifting back a few centimeters every year. You probably think that a day lasts 24 hours. But this is not exactly correct. The average day lasts 24 hours and 0.69 ms and this number is changing. Our days have slowly been getting longer because the earth’s rotation is slowing down. It’s slowing such that every 100 years our days get longer by 2 ms.
Billions of years ago, a day on earth lasted half as long as it does now (Almost 12 hours) and the moon was much much closer.
Why is the moon moving away from us and why is the earth’s rotation slowing down?
It’s because of the tides. The moon’s gravity pulls on the earth, but one side of the earth is closer to the moon. So the moon pulls on that side harder and pulls less on the opposite side. The result is that there’s a bulge near the moon. Now the earth and moon are both moving. The earth spins in a circle one time per day. The moon orbits in a circle one time every27 days.
The earth stretches towards the moon forming a bulge, but the earth is still rotating and so the bulge rotates along with it. It takes time for the earth to stretch itself towards the moon and it never has time to finish stretching because the earth keeps spinning. So the bulge is never perfectly aligned to the moon it keeps spinning ahead of the moon.
This is what slows down the earth’s rotation. One side of the bulge is closer to the moon. So gravity pulls more on that side and pulls less on the other. This creates a rotation force or a torque that slows down the earth’s rotation. This also affects the moon. The force of gravity on the moon doesn’t point directly to the center of the earth. It points slightly towards the bulge.
Now let’s separate this force into two orthogonal components. One component points towards the center of the earth. The other component is perpendicular. The first component is what’s keeping the moon in orbit. The second component is in the same direction that the moon is moving. So this force is pushing the moon forward. It is propelling the moon into a higher orbit and causing the moon to drift away.
Because we have a bulge on one side of the earth, the moon accelerates slightly towards that bulge. This propels the moon forward into a higher orbit causing it to drift away. Eventually, if we wait billions of years and nothing else changes, eventually, the earth’s rotation will slow down so much that it will rotate along with the moon.
One day on earth will last as long as a lunar month and one side of the earth will permanently face the moon. This is caused by tidal locking.
Tidal locking has already happened to the moon. It’s why we only see one side of the moon. A long long time ago, the moon was probably spinning pretty fast, but tidal forces slowed down the moon’s rotation until it’s rotation speed was the same as its orbiting speed. And so one side of the moon is locked in place it’s permanently facing the earth. The side of the moon is the only one you’ve ever seen. The moon has another side to it, but you’ve never seen it and this is normal. Every large moon in the solar system is tidally locked.
In theory, this could happen to the earth someday. If the earth was tidally locked to the moon, the moon would no longer rise and set. It wouldn’t move in the sky and only one side of the earth would ever see the moon.