<p>Moon always faces Earth with one side, its spin period equal its orbital period - this is what we learn at school.</p>

<p>But I know Nature rarely operates in absolutes. I'd find it hard to believe Moon wouldn't spin relative to Earth at least very slowly. I searched but found no data other than "doesn't", so I'd like to ask - does the Moon stay turned the same side precisely - or do, over many years, new features show at one edge? If it does, how long would it take to make a full turn?</p>

CC BY-SA 3.0
2013-10-18T12:37:29.747Z
This is already addressed in the accepted answer in [Why is only one side of the Moon visible from Earth?](http://astronomy.stackexchange.com/questions/16/why-is-only-one-side-of-the-moon-visible-from-earth), under the section about libration.
called2voyage
CC BY-SA 3.0
2013-10-18T12:50:21.230Z
@called2voyage: This is not what I meant!! Libration is a cyclic process strictly coupled with orbital period. I'm interested in a long-term process of full rotation, difference between period of rotation and period of revolution!
SF.
CC BY-SA 3.0
2013-10-18T12:56:19.240Z
Libration is the only effect that will allow you to see different sides of the moon. Tidal locking will stay in effect until the moon flies out of Earth orbit in the distant future: http://www.space.com/3373-earth-moon-destined-disintegrate.html
called2voyage
CC BY-SA 3.0
2013-10-18T12:56:39.443Z
Unless the Earth-Moon system is interrupted by some other process.
called2voyage
CC BY-SA 3.0
2013-10-18T12:59:27.117Z
@called2voyage: So, the rotation and revolution periods are equal **exactly**, all the way down to within error introduced by random gravitational influences of other bodies and kinetic energy of striking meteorites?
SF.
CC BY-SA 3.0
2013-10-18T13:01:36.430Z
Any gravitational influences affecting the Moon also affect the Earth, balancing the effect out.
called2voyage
CC BY-SA 3.0
2013-10-18T13:03:47.297Z
But, yes, the rotation and revolution periods are more or less equal with enough exactness for the lifetime of the Earth-Moon system.
called2voyage
CC BY-SA 3.0
2013-10-18T13:07:01.977Z
@called2voyage: That "more or less" is exactly what I asked. If the difference is indeed of order of less than one rotation per time of existence of the set, that can be truly approximated as "unmovable".
SF.
CC BY-SA 3.0
2013-10-18T13:10:30.260Z
That's exactly what I'm trying to tell you. It is effectively unmovable.
called2voyage
CC BY-SA 3.0
2013-10-18T13:11:21.667Z
Thank you - too bad the question is closed, that's the answer I wanted.
SF.
CC BY-SA 3.0
2013-10-18T13:18:19.177Z
The reason I had to close this is because that is the definition of tidal locking which is addressed in the other question.
called2voyage
CC BY-SA 3.0
2013-10-18T13:19:09.590Z
@called2voyage: "Over many years"?
SF.
CC BY-SA 3.0
2013-10-18T13:30:26.993Z
From Tildal's answer: "Tidal locking (or captured rotation) occurs when the gravitational gradient makes one side of an astronomical body **always** face another" and "This causes one hemisphere **constantly** to face the partner body."
called2voyage
<the-moon>
Is the moon rotation at complete standstill?
SF.
# Is the moon rotation at complete standstill?

(Asked by: username_0 on 2013-10-18)

Moon always faces Earth with one side, its spin period equal its orbital period - this is what we learn at school.

But I know Nature rarely operates in absolutes. I'd find it hard to believe Moon wouldn't spin relative to Earth at least very slowly. I searched but found no data other than "doesn't", so I'd like to ask - does the Moon stay turned the same side precisely - or do, over many years, new features show at one edge? If it does, how long would it take to make a full turn?

**Tags:** the-moon
> **Comments:**
> **username_1**: This is already addressed in the accepted answer in [Why is only one side of the Moon visible from Earth?](http://astronomy.stackexchange.com/questions/16/why-is-only-one-side-of-the-moon-visible-from-earth), under the section about libration.  
> **username_0**: @called2voyage: This is not what I meant!! Libration is a cyclic process strictly coupled with orbital period. I'm interested in a long-term process of full rotation, difference between period of rotation and period of revolution!  
> **username_1**: Libration is the only effect that will allow you to see different sides of the moon. Tidal locking will stay in effect until the moon flies out of Earth orbit in the distant future: http://www.space.com/3373-earth-moon-destined-disintegrate.html  
> **username_1**: Unless the Earth-Moon system is interrupted by some other process.  
> **username_0**: @called2voyage: So, the rotation and revolution periods are equal **exactly**, all the way down to within error introduced by random gravitational influences of other bodies and kinetic energy of striking meteorites?  
> **username_1**: Any gravitational influences affecting the Moon also affect the Earth, balancing the effect out.  
> **username_1**: But, yes, the rotation and revolution periods are more or less equal with enough exactness for the lifetime of the Earth-Moon system.  
> **username_0**: @called2voyage: That "more or less" is exactly what I asked. If the difference is indeed of order of less than one rotation per time of existence of the set, that can be truly approximated as "unmovable".  
> **username_1**: That's exactly what I'm trying to tell you. It is effectively unmovable.  
> **username_0**: Thank you - too bad the question is closed, that's the answer I wanted.  
> **username_1**: The reason I had to close this is because that is the definition of tidal locking which is addressed in the other question.  
> **username_0**: @called2voyage: "Over many years"?  
> **username_1**: From Tildal's answer: "Tidal locking (or captured rotation) occurs when the gravitational gradient makes one side of an astronomical body **always** face another" and "This causes one hemisphere **constantly** to face the partner body."  

---

## 0 answers

