Shishu Sansaar | Science
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Do you know why
do we see the same side of the Moon always? Because it rotates on its axis.
The Rotation of the Moon
The current views and theories state that the Moon rotates once about its axis for every orbit around the Earth. Here is a quote from a well respected astronomy website "Bad Astronomy" that won the 2004 Scientific American science & technology web award.
"How it works: If you go out on several different nights and look at the Moon, you will always see the same features, at about the same position. It looks as if the Moon doesn't rotate! Ah, but it does. This can be seen using a model. Grab two oranges (or apples, or baseballs, or whatever roughly spherical objects you have handy). Mark one with an "X"; this represents a feature on the Moon. Now put the other one down on a table; this is the Earth. Place the Moon model on the table about 30 centimeters (one foot) away with the X facing the Earth model. Now move the Moon model as if it were orbiting the Earth, taking care to make sure that the X faces the Earth model at all times.
Surprise! You'll see that to keep the X facing the Earth model, you have to rotate the Moon model as it goes around the Earth model. Furthermore, you can see you have to spin it exactly once every orbit to keep the X facing the Earth model. If you don't rotate it, the Moon model will show all of its "sides" to the Earth model as it goes around.
Now, I have been a bit tricky here. We are talking about two different frames of reference; one on the surface of the Earth looking out at the Moon, and one outside the Earth-Moon system looking in. You performed the experiment from the latter frame, and saw the Moon rotating. From the former, however, you can see for yourself the Moon does not rotate. What is being argued here is that in one frame the Moon rotates, in another it does not.
We've actually learned three things:
Now advance 4 years to 2008 and how views have changed, the Discovery Channel has done a documentary on extra solar planets and presented a theoretical planet locked by gravity where rotation of the planet does not occur. In this example, the star and the planet in a mutual orbit presents the same face of the planet. How does this occur with the current theories of Moon rotation?
Let's examine the current status quo for Moon rotation--
Lets go over a few of mankind's facts pertaining to motion. An orbit is where gravity curves a path of an object to revolve about a central point. The definition rotation considers the point of reference used, if the object rotating about a point of reference outside of the object this motion is an orbit. If the rotation is a reference point within the object, this is rotational spin.
Astronomers have made a basic mistake in orbital mechanics and when given the answer refuse consider that they are wrong. It has been a decade since some of you in the field have seen this paper and debated it on the forums, yet "Ask the Astronomer" still has not learned. The reference frame used included the Earth as the central point, yes a point on the Moon's surface rotates, but this is due to gravity curving the path of the Moon. The Moon does not rotate 360 degrees about its internal axis as rotational spin. Within in this frame of reference, the Moon's axis follows its rotational path as gravity turns the direction of motion of the Moon curving inward, but maintaining orbital distance. Astronomers again when giving a simple explanation involving the motion of the Moon contradict their own words describing orbital rotation and spin. The problem with the current theories on Moon rotation is that those who formulated this theory, confused completing a curved path of rotation around the Earth as the Moon was slowly turning with reference points of the Moon changing in relation to the planet. It is only the illusion of rotation as others in an expanded reference frame can revolve an object about a point and you seem to be turning it. The key here is turning it not spinning about its axis. This is simple orbital mechanics 101.
For the layman let examine a simple example a sphere will circle in the air about the point you standing. The painted side revolves faces you always. Now we replace the sphere with a helicopter it circles and we see the same side, but speeds up and slows and we still see the same side. Now observe the rotor if it is off the same blade faces us. Now let that rotor spin once about the axis of the helicopter with the closest blade marked. Once the helicopter made it half way around you find the marked blade on the far side of the copter only to show itself on the inside on completion of the circle. Only from above looking down do you see the copter heading first south, then turning west then north then east simulating rotation, but it is only a change in direction. You also saw that orbital velocity had nothing to do with seeing the same side due to synchronization of the rotational period and its spin about its axis for the Moon.
Experiment: If you have a stick, attach a line to one of its ends about a pivot point and connect the other end through the center of the ball and tie off. Revolve the ball about you, does ball spin about its axis? How could it, it is attached to a string. You do see the same face of the ball as it revolves about the holder of the stick. You can validate that a point on the ball when you include yourself and the ball's curved path, does change its position within the greater frame, but the ball itself does not spin about its axis. Spin is a relationship between a frame of reference that is within the object in question and its rotation is about a set point within that frame. It is not the motion of the total frame of reference as an object revolves in a circular path around a pivot point the Earth in this case giving the illusion of spin about the axis, when it is a change position due to rotation. Are you confusing motion of an object following a curved path as oppose to spin about its axis? I hope you answered no. So why do you use the same of conditions and principles to validate the Moon's rotation about the Earth and to validate the moon's spin about its axis are in perfect synchronization?
A Simplistic Model : A Description of Moon Rotation About its Axis
Lets consider a fresh approach to solving this problem.
In the lateral
diagrams A is the initial reference point and will be assigned a location of
zero degrees with measurements proceeding 360 degrees counter-clockwise back to
In the lateral diagrams
A is still the initial reference point on the face of the Moon, but has moved from
initial point @ 0 degree along the orbital path to point B is located @ 45 degree
in a counter-clockwise orbital direction.
In the lateral
diagrams A is still the initial reference point @ 0 degree to the surface of the
Earth, point B is located @ 90 degree, point C is located @ 180 degree and point
D is located @ 270 degree counter-clockwise along the Moon’s circumference.
Explanation of Frames of Reference
Here is an experiment that can be conducted in your elementary astronomy labs. Reviewing an object rotates when the reference point that spin occurs is within the object itself. Set up a simple clear rigid plastic 16 inch square sheet, 1/2 inch thick. Drill a hole in its center and attach a rigid rod. Drill a hole through center of a 2 inch wafer, the same diameter as the rod, glue several inches above the base to the rod. This will be a base. Drill just greater than the rod diameter through the center of a six inch or its closest centimeter equivalent in diameter hard plastic hollow sphere. At its equator, drill another hole 90 degrees to the central axis. Glue or epoxy a hard straw at to opposite attach a 2 inch Styrofoam ball glue in place.
Rotational spin within the object is defined as the axis line (a straight line drawn from pole to pole) moving away from the reference point and returning to while moving in one direction. In the absence of rotation, the points of the axis line and the initial reference point remain aligned. Now that a rigid rod is attached to the Styrofoam ball (the Moon) and the six inch plastic sphere (Earth) we expand our frame of reference. Spinning the Earth causes the Moon to orbit as the rod represents gravity that turns the path of the Moon into a curved path and at the completion of one revolution an orbit. Upon observation the same face of the Styrofoam ball representing the Moon is always pointed toward the plastic representation of Earth no matter what the orbital velocity that occurs.
Again as you notice the sphere representing the Moon does not spin about the axis within, you constantly see the reference point and the axis line are locked. If it did spin you would have to see all sides of the sphere from Earth. Looking at the total picture we find that a sphere with no rotation when pivoting about a point outside of the sphere presents the same view of the reference point and axis line. In the second part when the speed of the rotation of the sphere to complete 1 rotation within the grid was matched to pivoting about 360 degrees in synchronization you still see all sides. Now realize the Moon is the sphere within the grid and the pivot point is Earth not the Moon axis and this change the view of mankind's current observations? Can astronomers present a simple experiment with models that backs the how Moon rotates? No. Now we should finally move on.
For a simple experiment, spin an egg on a smooth surface to represent the forces affecting planetary cores. Stop it for a fractional second, then let the egg go. The core, which is spinning will drag the shell, thus rotation or in the case of a planet, its crust. This is rudimentary example explaining the principles of rotation in planetary and stellar objects.
Created by Sushma Gupta on January 15, 2002
Modified on 09/23/13