Why Can't We See The Far Side Of The Moon?

[zingo1327]

What I know (in an idiots fashion.)
The moon takes 28 days to orbit the Earth and 28 days to do one Moon rotation.
The moon can always be seen somewhere from Earth. weather permitting.
I see how it works if you treat the earths orbit like a clock face, spinning 9 o'clock,3 o'clock,9 o'clock,3 o'clock (East/West and the moons orbit as spinning 12 o'clock,six o'clock,12 o'clock,six o'clock.North/South, but I've been informed we both spin East to West (9 o'clock,3 o'clock,9 o'clock,3 o'clock)
If we run an imaginery line North/South around the moon and then split the face as we see it as A and B then logic says the splits hidden will be C+D.
My tiny brain then says the moon should have completed quarter of a moon rotation and quarter of an Earth orbit after 7 days,half a moon rotation and Earth orbit after 14 days,3/4 a moon rotation and Earth orbit after 21 days and back to where it started after 28 days.
I can't get my brain round, how after 7 days, we're not seeing sectors D and A, and after 14 days we're not seeing sectors C and D, and after 21 days we're not seeing sectors B and C.
After 28 days we're back to seeing sectors A and B.
I've tried looking at simulation sites but it still bamboozles me.
Can someone explain in simple terms or recommend a good simulation website.Sarcastic comments always welcome :-)

[Buenchico]

Does a simple picture help?
http://ircamera.as.arizona.edu/NatSci102/NatSci102/text/moonrotate.htm

[Teddio]

The Moon rotates on its axis anticlockwise, period approx 28 days. The Moon also orbits Earth in an anticlockwise direction, period approx 28 days. Therefore an observer on Earth will always see he same face of the Moon (not the case when observing Earth from the Moon)
Due to libration, one can usually see about two thirds of the face of the Moon during a year.

[rojash]

.. if not. Try to imagine the moon tethered to the earth by rigid pole. As the earth rotates, the moon rotates with it (orbits it), but in so doing, it also spins on it's own axis (it has to, because the pole forces it to). The side where the pole is attached will always be facing the earth.

[Clanad]

The term for this phenomena (as Chris' link comes close to stating) is "tidally locked".

It's eveident, given enough time, the Earth will become tidally locked to the Sun. Proven by this: [tex]\frac{\omega a^6 I Q}{3GM^2k_2 R^5}[/tex]

[DangerUXD]

look up "tidal lock", it's really very simple.

[vascop]

Rojash - Isn't what you said a bit misleading since if the moon were 'tethered' to the earth then the moon would orbit the earth in 24 hours, but it takes 28 days.

[mibn2cweus]

Why do we never see the Moon's backside? Why that would be obscene!

But it's been said, "With a powerful enough telescope you can see Uranus."

[Peter Pedant]

.

solvitur videndo
vel melius, solvitur respiciendo

it is solved by looking.....at the moon

[Zeno provided a proof that movement was not possible and some commentator later commented - it is solved by walking]

[whiskeryron]

http://youtu.be/CC8XF_5VhnA

WR.

[Old_Geezer]

Aye walking is a good illusion.

[Peter Pedant]

I thought old geezers comment was:

waking is a good illusion

and I thought how deep ! how deep !
but unfortunately it was walking.....

and those bases on the other side ! Mind blowing what one learns from peers on Answerbank.

[Teddio]

Mibs, you don't need a telescope to Uranus. Just turn your head through 180 degrees and bend over !

[bert_h]

Try this completely different thought experiment...

Draw a large circle on the ground, 10 or 15 feet across. This is going to be the orbit of the 'moon'.

Get a friend and stand him in the centre. He is going to be the 'earth'.

Stand on the circle, facing anticlockwise, and start walking on the line of the circle. Your friend is allowed to turn round and round if he wants to, at any speed he likes, which is the earth's rotation (and completely irrelevant, as you will see).

After one complete circuit, you will also have turned round once, just like the moon does every 28 days. Ask your friend if he could ever see your right side and shoulder! No, all he could ever see was your left side and shoulder.

[zingo1327]

no guys.I still don't get it

[New Judge]

The planet Mercury is also "tidally locked" to the Sun. Tidal locking eventually comes to all orbting bodies. It is caused by the gravitational forces stretching the bodies in the direction of the "pull". (This is called the "tidal effect" and can be seen quite clearly on the Earth by the rise and fall of the sea). This distorts the bodies and causes their rotation to slow down. It effects both bodies in the system and eventually the earth and moon will settle into "tidal unison". Eventually the Earth and Moon will have exactly the same rotational period, and this will also exactly equal the orbital period meaning both bodies will present the same face to each other for ever.

[mibn2cweus]

Hold a ball (or any object) at arms length while turning (yourself) completely around 360 degrees in place. The side of the ball facing you does not change throughout because its rate of rotation precisely matches its rate of revolution around you.

What difference (if any) do you perceive between how the ball appears as it moves around you to how the Moon appears as it orbits the Earth? If you turn your head to the right or left (to simulate Earth's rotation), does that change the side of the ball facing you?

[zingo1327]

If i hold the ball at arms length and i turn in a circle I will always see the same side of the ball...but if...as i turn in a circle, the ball in my hand also slowly turns i will eventually see the other side.That's what my brain is telling me

[mibn2cweus]

ingo1327
Question Author
If i hold the ball at arms length and i turn in a circle I will always see the same side of the ball...but if...as i turn in a circle, the ball in my hand also slowly turns i will eventually see the other side.That's what my brain is telling me
18:42 Thu 17th Jan 2013

But the ball does turn, (once per revolution) not your hand but your hand. If the ball did turn . . . then you would see the other side.

[mibn2cweus]

Sorry, AB edited my response, which was -

But the ball does turn, (once per revolution) not IN your hand but WITH your hand. If the ball did NOT turn . . . THEN you would see the other side.

[mibn2cweus]

It is because the Moon is rotating (once per revolution) that we see only one side.