# How and why Moon has reversed its position towards the Earth?

enotechris | Certified Educator

Current theory holds that the Moon was created by a large body smashing into the early Earth (this apparently is now known as the "Theia Collision.") The matter ejected from both bodies coalesced in close orbit to the Earth and became the Moon.   Its orbit around the Earth and rotation about its own axis was due to this primal impact, and rotate and revolve it did -- one calculation shows the early Moon revolving around the Earth in 10 hours!  Had humans (or any intelligent life) been able to withstand the lava lakes of Earth (there was no such thing as "land" then) and watch the Moon, they would have seen the Moon take up most of the sky and would have seen all sides of it as it rotated and revolved about Earth.  Billions of years later, the Moon still revolves around the Earth and rotates upon its own axis, but now we see only one side -- because the length of rotation and revolution are just about the same.  However, we can see about 59% of the Moon's surface from Earth, because of a process known as "libration" (from the Latin libra, meaning scales, suggesting a swinging back and forth.)  During the course of a month, we can see a little more of one side, then the other, of the disc of the Moon.  This visible "swinging" or rocking back and forth is actually the last slow remnant of that initial rapid spinning.  In time, this motion will decrease and eventually stop, and the Moon be completely "tidally locked" to the Earth, showing only 50% of its surface.

To visualize, spin the front wheel of your bicycle.  Its rapid motion will slowly decrease and eventually stop.  Before it stops completely, however, they'll be a point where the wheel can't make a complete revolution -- it will go up, slow, stop, and and rotate in the opposite direction, where it will go up, slow, stop, and reverse direction again.  The swings will become less and less until the wheel comes to rest.  If you could attach a tennis ball or the like to the rim and hold the spinning wheel overhead above your face, looking at the rim edge on, while extending your arms, you'd get a good approximation and summary of the billion year history of Lunar motion.

jseligmann | Certified Educator

As far as I know, the moon never reversed its position in relationship to the earth. Over millions of years, the moon has gradually moved farther away from the earth, and, in doing so, its orbit around the earth has slowed. But there is no reversal of anything in this regard.

And as to the nearside/farside relationship between the earth and the moon, that has never reversed either. Because of gravitational forces, one side of the moon always faces the earth (we call that the nearside) and the other side of the moon faces away from the earth (we call that the farside). This means that, in its revolution around the earth, the moon rotates on its axis only once. This has not reversed either.

astrosonuthird | Student

It is naturally by being hitted by an asteroid.

astrosonu | Student

Because it was hit by an asteroid.

giorgiana1976 | Student

The mysterious far side of the Moon has always attracted the interest of astronomers and science fiction writers, because it was never directed towards Earth. Scientists think that the far side of the Moon was directed towards our planet before an asteroid  to return it in the opposite direction.

An analysis of impact craters shows that our natural satellite achieved a return of 180 degrees.
Mark Wieczorek and Matthieu Le Feuvre of Institute of Earth Physics in Paris
analyzed the age and distribution of 46 of the craters on the Moon, identified so far.

Knowing that is directed in the orbital direction, western hemisphere of the Moon would have to show more craters than the East. Scientists have found several craters on the west side, but all very young, most of old craters being concentrated in the eastern hemisphere. Starting here, French researchers have concluded that the east of the moon has experienced in the past several "strikes" than the west side.

This finding could be explained by an asteroid impact, which turned Moon backwards. Such an impact would considerably had increased rate of rotation of the moon, but over a few tens of thousands of years,from Earth, this movement would be observed as an extremely slow movement. Last, Moon stopped in position which is now.
The far hemisphere of the Moon was first photographed by the Soviet probe Luna 3 in 1959, but it could not be observed directly by the human eye until Apollo 8 mission, in 1968. The Eastern Hemisphere of the Moon presents the largest impact crater in the solar system, with a diameter of 2,500 km and a depth of 12 kilometers.