Far side of the moon

[monty0703]

If the the moon turns on it's axis once per orbit, doesn't that mean that the far side faces us at some point?

[monty0703]

I know that this has been asked before but I still don't get it. I know the moon is tidally locked etc.. but I can't get my head around the fact that if the moon rotates, why the far side isn't pointing in our direction at some point. My head hurts...

[knobster]

Maybe its axis is in a different position to ours and it rotates different to us.

Just a passing thought

[monty0703]

but even though the axis is different, if it is rotating then shouldn't the side we always see move out of view from us at some point?

[knobster]

We rotate from east to west or west to east not quite sure what I am trying to say is what if the moon rotates from north to south.

Well thats the only reason I can think off why that happens.

[dundurn]

Imagine there's a football stuck on the end of Big Ben's minute hand with the side facing the centre of the clock painted a different colour to the side facing away from it. If you watch the ball over the course of an hour from the street you'll see that it rotates once, but at no time could you see the 'backside' of the ball if you were standing at the centre of the clock. The moon does exactly the same relative to the Earth.

Two points to make clear:
The different colours have nothing to do with which half of the moon is illuminated by the Sun.
Not being stuck on the end of a minute hand, the moon in actual fact does have a slight 'wobble' in its rotation which results in our seeing 'round the edge' some of the time. As a result we can in fact see about 56% of the moon's surface from Earth.

[knobster]

Well bang goes my theory then.

[tinglepie]

football....... bigben......... Im outa here

[knobster]

I found this monty.

http://www.wonderquest.com/MoonSpin.htm

[knobster]

Whys that gravy are the daleks chasing you again?

[joggerjayne]

There are lots of little green men living on the Dark Side.

They probably control it.

Dundurn's explanation is spot on. If the Moon always faced in the same direction, when it got round the other side of its orbit, the people on the other side of the world would see the other side of it.

Hold you two fists out in front of you. Your right thumb faces your left hand. Now cross your hands over. Now, your right little finger is facing your left hand. So in order for your feft hand to see the same view of your right hand, your right hand would have had to turn through 180 degrees.

Just like the Moon !!

[monty0703]

Arggghhh! My head hurts and I'm getting odd looks from colleagues who don't know that my clenched fists are trying to help me understand the moon thing!

[knobster]

I think montys question has been invaded from the dark side off chatterbank.

[monty0703]

"If the Moon always faced in the same direction, when it got round the other side of its orbit, the people on the other side of the world would see the other side of it."

ok, I get this and get that the 'dark side' isn't always dark. But if the moon is spinning on its axis as it orbits the earth, wouldn't the 'dark side' face us at some point?

I'm not usually this dense..honestly!

[joggerjayne]

It doesn't "spin" like a spinning top.

It rotates slowly.

In the time it takes you to swap your fists over, it has "spun" precisely one half turn, so that your right thumb (the near side of the Moon) continues to face your left fist (the Earth).

[R1Geezer]

Monty, focus on Dundurns answer only, imagine you are sitting at the base of the minute hand looking at the ball. You are on Earth and the ball is the moon. You always see the same side, it's really not that difficult. Do not think of the moon as spinning at all in the normal sense. Yes I know it does actually do one revolution per orbit but relative to a viewer on earth it appears not.

[Octavius]

It�s a matter of language.

If you sit on the nearside of the moon - where we on Earth could �see� you - and waited two weeks to stand up, then at the time you stand up, you would be on the far side and we wouldn�t be able to see you. If you sat down again, in two weeks time we would be able to see you again.

So, yes, we do see the far side of the moon, but only when that far side has rotated to the near side. At any given point there is always going to be �side� we can see and a side we can�t , but effectively they take it in turns.

So we only see the nearside, which at several points in time has been the farside, but semantically speaking, we can�t �see the far side� unless we send a probe round to the back of the moon, which scientists have done.

[monty0703]

Aha!! Finally the penny has dropped. Thanks to everyone. I'm sure I heard the noise of heads banging against walls when I was reading the answers..

[R1Geezer]

WTF are you on about octavius?

[joggerjayne]

I'm not sure that's right, Octy.

When you stand up, the Moon has travelled half way round it's orbit, and rotated half way round it's "spin", so the person on the Moon is still facing the Earth when he stands up.

I say "he" because no woman would be daft enough to take part.

[Octavius]

No you are right Jayne.

I and monty, clearly need to read up on synchronous rotation.

Ignore my last post, althogh surely worthy of an 'A' in drivel.