月球真的在旋转么？

鲍海飞 编译 2011-8-30

月球有好多神奇之处，比如，它在地球和太阳之间所处的位置，比如，月球上没有磁场等；还有好多疑问：比如，月球到底是不是空的，月球是否是外星人的基地等。不过，还有一个似乎更浅显得问题，月球在旋转吗？也就是为什么只能永远看见月亮的唯一的半张脸？

月球在旋转么？这个看起来似乎很简单的问题，里面却隐藏着很大的玄机。事物都在运动，这是肯定的。但是月球在旋转吗?更确切地说月球在自转吗？

人们所熟知的，月球环绕着地球旋转，旋转周期大致为28天，而且更为奇特的是，人们只能够看到月球那永远朝向地球的那一半脸，也就是说，只要在地球上，你永远看不见月球的另一面。但是，有相当一部分人认为，这是因为月球的自转周期也恰好是28天，所以，你只能看到这半张脸。

据说，太空飞行员在天空中能够看到月球的旋转，但其实只是一个假象。

有一个例子，似乎可以用来说明这个问题。拿两个桔子，一个当作地球，放在桌子中间，另一个当作月亮，放在桌子的边上，并在这个桔子上刻一个记号。然后，拿起这个桔子绕着桌子中间的桔子（地球）旋转，你会发现，为了使‘月亮’这个刻有记号的桔子的一侧要始终对着中间这个桔子‘地球’的话，你就需要不停地旋转这个桔子，这样，才能保证月亮这半张带有记号的脸始终对着地球。如果不一直选转下去的话，你就将看到这个桔子的所有侧面。

自转的定义应该是物体环绕自身的某个点（或者中心）进行的圆周运动，而此时月亮似乎环绕着一个不在自身之上的一个点在旋转（应该称为轨道），这样的旋转是自转吗？（电子就有自旋磁矩和轨道磁矩！）

这里有一个问题值得考虑，就是观察的参照系。如果以地球为中心去观察月亮，那么，我们看它确实不动，因此，永远是这唯一的半张脸。但是如果把地球和月球放在一起，而你在一个所谓的外部空间去观察的时候，那么，你会发现月亮在环绕着地球在旋转，同时，月亮似乎也在自转。坐标系的选取的确会带来观察的混淆。

不过，有一个大家都熟悉的例子，也许能够直接证明这一点。月球其实根本就没有旋转。用一根绳子拴住一个石头，然后你站在中间把石头旋转起来，这个时候，你面对着的石头一直在朝向你，石头不会发生旋转，这种情况也应该适合月球，是地球和月球之间的相互引力导致这样的结果。

The Rotation of the Moon

The Brief: Today’s astronomers explain the Moon’s rotation about its axis with one side visible to Earth. The theory states, the moon spins about its axis in synchronization with its orbital period around the Earth. This revolution or slow spin of the axis of the Moon allegedly turns precisely at a rate, which keeps the same side always facing the Earth. We examine this theory to address the truth behind this hypothesis or present a new solution.

The current views and theories states 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:
# 1) the Moon rotates as it orbits the Earth (as seen by an outside observer);
# 2) it rotates one time for every orbit (to that observer); and
# 3) if it didn't rotate, we would eventually see all of the Moon as it orbited the Earth. "

Let's examine the current status quo for Moon rotation

Currently in 2011, the status quo within the field of Astronomy is that the Moon spins about its axis in a period equal to its approximate 27.322 day rotational period around Earth. So lets looks at the frame of reference used in current theories within the field of Astronomy that has backed this conclusion. When scientists concluded the axis is the Moon rotated in pace with its orbit presenting the same side always, this seemed true, but it was the frame of reference used, which is the source of confusion.

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.

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?