Try this little thought experiment.
Imagine you are sitting on the side of the moon facing away from the earth. The stars are bright and steady, yet over a 28 day period they move across your sky. You decide to take a long exposure photograph of the stars and you find that they appear to rotate about a common lunar axis. This is of course, self evident.
From this, you conclude which of the following:
A) The cosmos is rotating about an axial of the moon
B) The moon is rotating about it's own axis.
also
Or something else?
C) – The moon is ONLY *revolving* around the combined mass of the Earth and the moon, which is called a *barycenter*. The Earth-moon barycenter is a foci (or axis) which is within the Earth – in this graphic the
red + marks the foci of common mass of the Earth-moon barycenter:
The larger white body (
representing the Earth) is also rotating around its polar axis as the moon orbits around the Earth. The smaller white body (
the moon) is NOT rotating around its polar axis as it orbits the Earth – if the moon *still* both rotated as it orbited, then we would see more than one face of the moon.
{NOTE – until it was tidally-braked, billions of years ago, our moon did both orbit (revolve) as it rotated around its polar axis.}
If you still don't understand the differences between *REVOLVE* and *ROTATE* (
two different types of circular motions), this next graphic shows a sphere *ROTATING* around its internal polar axis:
---Rotaion & Axis---
"A rotation is a movement of an object in a circular motion. A two-dimensional object rotates around a center (or point) of rotation. A three-dimensional object rotates around a line called an axis.
If the axis of rotation is within the body, the body is said to rotate upon itself, or spin—which implies relative speed and perhaps free-movement with angular momentum.
A circular motion about an external point, e.g. the Earth about the Sun, is called an orbit or more properly an orbital revolution." (Emphasis added.)
http://en.wikipedia.org/wiki/Axis_of_rotation
--/--
Your orange-in-hand analogy is completely flawed because your hand is a co-rotating reference with the earth and the orange, err, moon.
NO, the orange (and your hand) are instead *REVOLVING* 360˚ around the combined mass of your body and orange, and that axis of common-mass would be a foci within your spinning body. The moon's circular motion is exactly the same as our moon's circular motion around the Earth.
The moon clearly does not rotate about an axial reference that is itself locked to the earths axis (your arm and palm in your analogy).
The moon does not *ROTATE* around any axis, but the moon does *REVOLVE* around a point exterior to its mass, and the center-point of that orbit is the barycenter within the Earth.
Sloppy verbiage is a sign of sloppy thinking – "
The Earth *ROTATES* on its polar axis as it *REVOLVES* around the sun."
If you insist on using "rotate" (
which is a circular movement around an INTERNAL AXIS) when the word "revolve" (
around an EXTERNAL AXIS) would be a more suitable choice of words, then please do me the courtesy of identifying the EXACT location of the rotation's axis that you're then talking about.
For example, your "B" choice above could mean anything:
superluminal: "
B) The moon is rotating about it's (sic) own axis."
If you mean the moon's internal axis, then NO!
If you instead mean the axis of the moon's circular motion is the barycenter within the Earth, then YES!
However it does exhibit libration, which can only occurr if the rotation of the moon about it's own axis occasionally lags and leads this rotation as it orbits the earth. Otherwise, how do you explain the periodic axial oscillations of something as massive as the moon?
As I noted early on in this discussion, Libration is interesting, but it has nothing to do with whether, or not, the moon is turning a full 360˚ around its INTERNAL polar axis as the moon also *REVOLVES* (orbits) around the Earth each month.
By what mechanism does the enormous mass of the moon stop and reverse and then stop and reverse again???
So what are we missing ken? You need to do a better job of explainig why we are all wrong.
Eagerly awaiting some better explanatory discourse from you. Thx.
You could start by polishing up on your English skills in order to correctly use the words "rotate" or "revolve" where suitable.
If you can master English, then we can compare the relevant circular motions involved, from both the sidereal and center-point perspectives, to see how they differ, and then perhaps we can agree whether this is a zero-rotating body, as it's labeled to be (a 0:1 spin rate):
The moon in that so-called "Zero rotation" graphic is actually *ROTATING* around its internal polar axis clockwise, one time per each counter-clockwise orbit.
Interestingly, the planet Venus' retrograde rotation is only a tad faster than that zero-rotating moon's rotation:
http://www.geocities.com/kfuller2001/tVenus.html
Thus, if Venus continues to slow its rotation due to tidal locking with the sun, then Venus will spin down from its current
.93:1 rate (just short of two 360 ˚rotations per orbit) and eventually Venus will slow to a 0:1 spin rate. HOWEVER, since a sidereal spin rate of 0:1 means Venus will still be rotating one time per orbit (as viewed from the sun), Venus will continue to spin down until Venus finally stops at a 1:1 sidereal spin rate.
When Venus finally stops at a 1:1 spin rate (as viewed from the sidereal perspective), the tidal bulges caused by the sun's gravity will finally stop traveling around Venus' circumference and become locked into Venus' surface facing towards the sun. Until that happens, Venus will remain the most perfectly rounded sphere in our solar system. AFTER Venus finally stops rotating at a 1:1 spin rate, at that point Venus will loose its perfectly round shape and form a prolate spheroid:
http://en.wikipedia.org/wiki/Prolate
Ken