Does the Moon Rotate?

[jtb]

The moon revolves--changes direction--but does not rotate.

A person at the center of an oval track (earth) racing CW will see the right side of a horse (moon) in every direction.

A person anywhere in the bleachers (external view) will see the right side of the horse at the farthest point of the track, the head when approaching, the left side when closest, and the tail when departing. One rotation per revolution. However, common sense tells us the horse is changing direction, not rotating. The same can be said for the moon.
jtb

[Goldminer]

The moon revolves--changes direction--but does not rotate.

A person at the center of an oval track (earth) racing CW will see the right side of a horse (moon) in every direction.

A person anywhere in the bleachers (external view) will see the right side of the horse at the farthest point of the track, the head when approaching, the left side when closest, and the tail when departing. One rotation per revolution. However, common sense tells us the horse is changing direction, not rotating. The same can be said for the moon.
jtb

So, jtb, if the Moon kept the same portion of its surface presented to the Sun as it orbited the Earth, would you then say it is rotating? (We would then get to see the hidden side of the Moon.)

[jtb]

So, jtb, if the Moon kept the same portion of its surface presented to the Sun as it orbited the Earth, would you then say it is rotating? (We would then get to see the hidden side of the Moon.)

Goldminer, good question. If the observer in the bleachers of the horse race (sun) were to walk around the outside of the track, they to, would only see one side of the horse (moon)--the left side. The observer at the center of the track (earth) would still see the right side of the horse. The horse is not rotating, it is merely changing direction.
jtb

[Goldminer]

So, jtb, if the Moon kept the same portion of its surface presented to the Sun as it orbited the Earth, would you then say it is rotating? (We would then get to see the hidden side of the Moon.)

Goldminer, good question. If the observer in the bleachers of the horse race (sun) were to walk around the outside of the track, they to, would only see one side of the horse (moon)--the left side. The observer at the center of the track (earth) would still see the right side of the horse. The horse is not rotating, it is merely changing direction.
jtb

You dodged the question, didn't you? The observer at the center of the track, in your scenario, made one revolution, per orbit of the horse, just as the horse made one revolution per orbit. Now, if the horse didn't "change direction" (rotate) as it orbited the track; we would get to see both sides of the horse from the center of the track, as we revolved watching the horse, wouldn't we?

[Michael V]

The moon has no "axial" rotation, but it does have an orbital rotation around the Earth.

The terms "rotate" and "revolve" are insufficient without adjective qualification.

thefreedictionary.com says:
REVOLVE:
1. To orbit a central point.
2. To turn on an axis; rotate.
3. To recur in cycles or at periodic intervals.
4. To be held in the mind and considered in turn.
5. To be centred.
ROTATE:
1. To turn around on an axis or centre.
2. To proceed in sequence; take turns or alternate.

The words "rotate" and "revolve" are simply English words with a similar and overlapping definition. That a protocol or convention may or may not exist within scientific circles as to which word should be used preferentially in any given context does not preclude an individuals freedom to use these descriptors as they wish.

Personally, I don't see how the horse racing metaphor is useful, but you are free to visualise in any way that helps you. However, the thread title is not valid. The Moon does not rotate around its own axis and it does not revolve around its own axis. The Moon does rotate around the Earth with one side permanently facing the Earth and it does revolve around the Earth with one side permanently facing the Earth.

Michael

[sjw40364]

Yes it rotates, if it did not rotate, but circled the earth, a new face would be seen at every portion of its orbit. It's orbital period just happens to match its rotational period, hence one face is always presented.
Doubt this? Take two balls, place an X on one, orbit that ball around the other without revolving it about itself. The X will NOT keep the same face towards the other ball UNLESS you also rotate it around its own axis as it revolves around the other ball.

[Michael V]

sjw,

You are quite correct and I am most embarrassed for focusing my comments on semantic trivia.
I must also apologise to jtb for dissing the validity of the thread title.

So the multiple choice question is:

1) Does the Moon rotate about its axis at the exact same rate as its orbital period.

or

2) Is the Earth facing side of the Moon "locked" by an interaction with the Earth that effectively simulates an axial rotation during the period of an orbital rotation, but the Moon is not itself axially rotating. Instead the Moon is "dragged" around in its orbit.


I was thinking that, although 1 and 2 are similar to each other, they are not the same thing, and I was of the opinion that 2) is correct, but having thought about it a bit more, I am less confident.....although I still lean toward option 2. No, I've changed my mind, its 1).....or 2).... Well, its probably 2), but it might be 1).

Michael

[jtb]

You dodged the question, didn't you? The observer at the center of the track, in your scenario, made one revolution, per orbit of the horse, just as the horse made one revolution per orbit. Now, if the horse didn't "change direction" (rotate) as it orbited the track; we would get to see both sides of the horse from the center of the track, as we revolved watching the horse, wouldn't we?

Goldminer, imagine a string attached from the observer at the center of the track to the horse. If the observer made one revolution and the horse made one revolution, only one side of the horse would be visible to the observer.

If the race track (orbit of the moon) were revolving around the guy in the bleachers (sun), the guy in the bleachers would see all sides of the horse changing direction--one entire vision of the horse per revolution.
jtb

[Goldminer]

You dodged the question, didn't you? The observer at the center of the track, in your scenario, made one revolution, per orbit of the horse, just as the horse made one revolution per orbit. Now, if the horse didn't "change direction" (rotate) as it orbited the track; we would get to see both sides of the horse from the center of the track, as we revolved watching the horse, wouldn't we?

Goldminer, imagine a string attached from the observer at the center of the track to the horse. If the observer made one revolution and the horse made one revolution, only one side of the horse would be visible to the observer.

If the race track (orbit of the moon) were revolving around the guy in the bleachers (sun), the guy in the bleachers would see all sides of the horse changing direction--one entire vision of the horse per revolution.
jtb

IMHO, you are beating a dead horse.

[Michael V]

I am interpreting peoples opinions correctly (please do correct me if I am wrong):

swj: the Moon rotates on its axis exactly once per orbit
Goldminer: the Moon rotates on its axis exactly once per orbit
jtb: the Moon is "dragged" sideways along its orbit with one face locked to the Earth
Michael V: the Moon is "dragged" sideways along its orbit with one face locked to the Earth

So it's a dead-heat....or ?

Michael V

[Goldminer]

I am interpreting peoples opinions correctly (please do correct me if I am wrong):

swj: the Moon rotates on its axis exactly once per orbit
Goldminer: the Moon rotates on its axis exactly once per orbit
jtb: the Moon is "dragged" sideways along its orbit with one face locked to the Earth
Michael V: the Moon is "dragged" sideways along its orbit with one face locked to the Earth

So it's a dead-heat....or ?

Michael V

Does the Moon rotate?(link)

If you guys want to make up the definitions of the words you use as you go along, you can claim anything. That's how Commies and Economists do it. Especially the head of the Fed. Oh, yeah, astronomers too, but not in this case.

[flyingcloud]

for a better perspective try a different view

[D_Archer]

Take a carousel ride.

Regards,
Daniel

[seasmith]

Synchronous rotation on video:

http://www.youtube.com/watch?v=OZIB_leg75Q

[jtb]

Many sites explaining tidal locking of planetary satellites require billions of years for synchronous rotation to take place. I guess in a Big Bang scenario with black holes and dark energy anything is possible given enough time. There is just too much evidence, such as decrease in the earth's magnetic strength, that indicates the earth is much younger than 2 billion years. Even the Bible doesn't mention the word "moon" until after Noah's flood.

Goldminer is right. We're beating a dead horse.
jtb