Why the moon keeps the same side toward earth?

Can we prove that mathemathically?


And, for same relation - sun and earth - , after so many

years.. the earth may toward same side to the sun?

junhwi wrote:

Why the moon keeps the same side toward earth?

It keeps the same side facing Earth all the time, because it rotates
once during the time it takes it to orbit once around Earth. A much
more interesting question is. "What hypothetical history of the Moon
might account for this observed fact?"

Can we prove that mathemathically?

It is a direct observation.

And, for same relation - sun and earth - , after so many

years.. the earth may toward same side to the sun?

Obviously, the Earth has had a very different history (in relation to
the Sun) than the Moon has had (in relation to the Earth).

--
John Popelish

junhwi wrote:

Why the moon keeps the same side toward earth?

Can we prove that mathemathically?

And, for same relation - sun and earth - , after so many
years.. the earth may toward same side to the sun?

Ref: http://imagine.gsfc.nasa.gov/docs/as...s/980218b.html

Most of the satellites in the solar system rotate synchronously like
our moon (see http://www.seds.org/nineplanets/nineplanets/luna.html).
An example of one that doesn't is Saturn's moon Hyperion. Its rotation
is actually chaotic. You can find out more about it at
http://www.seds.org/nineplanets/nine.../hyperion.html

Also, http://www.solarviews.com/eng/data1.htm#orb

which is a table of orbital and rotation periods, among other things.

Damian Audley and John Cannizzo
for Ask a High-Energy Astronomer

junhwi wrote:

Why the moon keeps the same side toward earth?

Can we prove that mathemathically?

And, for same relation - sun and earth - , after so many

years.. the earth may toward same side to the sun?

1) Lunar orbital locking.
2) Lunar libration.

Google
"lunar libration" 754 hits

3) Why do you think the side of the moon facing the Earth is all
smooth (less cratering after the fact), and the side of the moon
facing away from the Earth is nothing but violently craggy topography?

The Earth-Sun system does not embrace Earth-moon orbital conditions
for obvious reasons.

--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
"Quis custodiet ipsos custodes?" The Net!

Uncle Al wrote in message ...
junhwi wrote:

Why the moon keeps the same side toward earth?

Can we prove that mathemathically?

And, for same relation - sun and earth - , after so many

years.. the earth may toward same side to the sun?

1) Lunar orbital locking.
2) Lunar libration.

Google
"lunar libration" 754 hits

3) Why do you think the side of the moon facing the Earth is all
smooth (less cratering after the fact), and the side of the moon
facing away from the Earth is nothing but violently craggy topography?


I've read that one reason is that the Earth-facing-hemisphere gets one
or two lunar eclipses a year. That increases the thermal cycling and
attendant thermal erosion by over 8%; and the thermal cycling from an
eclipse is more abrupt than that from a lunar sunrise/sunset...

Any meteorites hitting the Earth-side would have to make a loop around
the moon, or skim past the earth. Calculating the magnitude of this
effect is certainly beyond me...


The Earth-Sun system does not embrace Earth-moon orbital conditions
for obvious reasons.

"junhwi" wrote in message
...
Why the moon keeps the same side toward earth?

It does not. There is a slight "wobble" such that over a period more than
half of the surface of the moon is visible.
However, read up on tidal mode locking.


Can we prove that mathemathically?

Yes.

"Mu-Pi" wrote in message ...
"junhwi" wrote in message
...
Why the moon keeps the same side toward earth?

It does not. There is a slight "wobble" such that over a period more than
half of the surface of the moon is visible.
However, read up on tidal mode locking.


Can we prove that mathemathically?

Yes.
--------------
ok lets see the mathematical prove.
if i may suggest a guess:

there is some asymetry in the mass distribution of the moon.?

TIA
Y.porat
------------------------

"Y.Porat" wrote in message
om...
"Mu-Pi" wrote in message
...
"junhwi" wrote in message
...
Why the moon keeps the same side toward earth?

It does not. There is a slight "wobble" such that over a period more
than
half of the surface of the moon is visible.
However, read up on tidal mode locking.


Can we prove that mathemathically?

Yes.
--------------
ok lets see the mathematical prove.

You first.

if i may suggest a guess:

there is some asymetry in the mass distribution of the moon.?

Of course. But tidal lock happens regardless of the mass distribution.

Read up on tidal forces.

"Rene Meyer" wrote in message
...

On Sun, 30 Nov 2003 23:43:58 +0900, junhwi wrote:
Why the moon keeps the same side toward earth?

Physics doesn't answer "Why"-questions. It describes the world.
The moon has a 29 day orbit and a 29 day rotation period.

Why " Physics doesn't answer "Why"-questions " eh?

Anyway, you's wrong Mr.Meyer, 'cos physics do answer this one....

If the moon where a perfect sphere then the impact of any
meteorite with a tangential component to the moon's surface
(and clearly there have been a good few of these in the moon's
history) would, by conservation of angular momentum, cause
the moon to rotate slowly, gradually revealing the whole of the
moon's surface to earth bound observers.

The reason the moon actually keeps the same side toward the earth
is that the moon is not a sphere but rather it is a prolate spheroid
(ie shaped like a rugby ball) with the major axis pointing towards
the earth. Newton's law of gravity reveals that any disturbance which causes
the major axis to rotate away from pointing at the center of the earth
results in a gravitational torque restoring the original orientation.
Thus in spite of metorite collisions the major axis of the moon remains
pointing more of less directly at the center of the earth, allbeit with a
little bit of "wobble", which is, in fact, an observered phenomena, as
mentioned by Mr.Wormley.


There are of course some "why" questions that physics doesn't answer,
like "Why is the velocity of light constant relative to all observers eh?"

;-)

--

keith stein
http://groups.google.com/groups?q=ke...&site=group s

On Sun, 30 Nov 2003 23:43:58 +0900, junhwi wrote:
Why the moon keeps the same side toward earth?

Physics doesn't answer "Why"-questions. It describes the world.
The moon has a 29 day orbit and a 29 day rotation period.

Can we prove that mathemathically?

We know this by observation.

Rene.

--
René Meyer
Student of Physics & Mathematics
Zhejiang University, Hangzhou, China