<p>Tidally locked means that it's always facing Earth with the same side.</p>
<p>We know it circles Earth because we know there are lunar and solar eclipses.</p>
<p>Thus it cannot circle Earth, be tidally locked AND NOT rotate around its own axis (as it needs to revolve once around its axis in one revolution around earth in order to show the same side to us all the time).</p>
<p>Think of this easy-to-test analogy: Try walking around a tree, facing it all the time. Now consider the directions your face points to when doing so. You cannot face the tree all the time time AND NOT having had your face oriented once North, once West, once East and once South. You thus faced the tree all the time and doing so made one rotation around your own axis while circling the tree.</p>
<p>Thus, if you assume a spherical body and the Moon circling Earth, then you have to assume it rotates around its axis. Even with a geo-centric model of the universe the Moon was assumed to rotate around Earth and this thought and argument can have been made; the Greeks surely knew about this, even if they assumed as Ptolemaios that the Moon circles in or on its Moonsphere around Earth.</p>

CC BY-SA 4.0
2022-09-11T14:41:14.213Z
2022-09-11T15:36:27.150Z
2022-09-11T15:36:27.150Z
planetmaker
<p>Since our Moon is tidally locked with earth, we always see only one side of the Moon. In such a case, how and when did mankind first realize that the Moon is also revolving around its own axis? or for that matter, it is revolving around earth as well? Although we (humans) might have logically deduced that the Moon will have an <strong>hidden side</strong> (<strong>the side behind the visible side</strong>), but that need not mean that the moon is revolving. It could simply be that only one side of the Moon is facing earth...- as if it is permanently locked in that position. What made us imagine it could be revolving around itself and around Earth?</p>

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2022-09-11T14:54:05.090Z
Can you please explain a bit the difference to your previous question? https://astronomy.stackexchange.com/questions/44361/moons-rotation-and-revolution
planetmaker
CC BY-SA 4.0
2022-09-11T17:36:23.053Z
@Planet maker: Not much of a difference in my earlier question and the fresh one. May be this one is more clearer. Unfortunately I am not convinced/satisfied with the answers - NEITHER THEN, NOR NOW...
Niranjan
CC BY-SA 4.0
2022-09-11T17:36:52.310Z
@James K: Not much of a difference in my earlier question and the fresh one. May be this one is more clearer. Unfortunately I am not convinced/satisfied with the answers - NEITHER THEN, NOR NOW...
Niranjan
CC BY-SA 4.0
2022-09-11T17:42:07.563Z
I think your confusion is **locked** doesn't mean **not rotating**.  It **is** permanently locked in position, therefore it **is** rotating.
James K
<the-moon><tidal-locking>
Tidal locking of Moon
Niranjan
# Tidal locking of Moon

(Asked by: username_0 on 2022-09-11)

Since our Moon is tidally locked with earth, we always see only one side of the Moon. In such a case, how and when did mankind first realize that the Moon is also revolving around its own axis? or for that matter, it is revolving around earth as well? Although we (humans) might have logically deduced that the Moon will have an **hidden side** (**the side behind the visible side**), but that need not mean that the moon is revolving. It could simply be that only one side of the Moon is facing earth...- as if it is permanently locked in that position. What made us imagine it could be revolving around itself and around Earth?

**Tags:** the-moon, tidal-locking

> **Comments:**
> **username_1**: Can you please explain a bit the difference to your previous question? https://astronomy.stackexchange.com/questions/44361/moons-rotation-and-revolution  
> **username_0**: @Planet maker: Not much of a difference in my earlier question and the fresh one. May be this one is more clearer. Unfortunately I am not convinced/satisfied with the answers - NEITHER THEN, NOR NOW...  
> **username_0**: @username_2: Not much of a difference in my earlier question and the fresh one. May be this one is more clearer. Unfortunately I am not convinced/satisfied with the answers - NEITHER THEN, NOR NOW...  
> **username_2**: I think your confusion is **locked** doesn't mean **not rotating**.  It **is** permanently locked in position, therefore it **is** rotating.  

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## 1 answers

### Answer by username_1 on 2022-09-11. Score: 4

Tidally locked means that it's always facing Earth with the same side.

We know it circles Earth because we know there are lunar and solar eclipses.

Thus it cannot circle Earth, be tidally locked AND NOT rotate around its own axis (as it needs to revolve once around its axis in one revolution around earth in order to show the same side to us all the time).

Think of this easy-to-test analogy: Try walking around a tree, facing it all the time. Now consider the directions your face points to when doing so. You cannot face the tree all the time time AND NOT having had your face oriented once North, once West, once East and once South. You thus faced the tree all the time and doing so made one rotation around your own axis while circling the tree.

Thus, if you assume a spherical body and the Moon circling Earth, then you have to assume it rotates around its axis. Even with a geo-centric model of the universe the Moon was assumed to rotate around Earth and this thought and argument can have been made; the Greeks surely knew about this, even if they assumed as Ptolemaios that the Moon circles in or on its Moonsphere around Earth.


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