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Author Topic: Why is the near side of the moon cratered & why is it always facing us?  (Read 9708 times)

Offline John Chapman

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If you look at a full moon it is completely pock-marked with craters. But here's what I don't understand: The near side of the moon always faces us. But surely the near side is shielded by The Earth, which is 3 or 4 time larger. Meteorites, etc, would have to pass through us to land on the man-on-the-moon's face. So why is it so cratered?

Also, if the same side is always facing us then it figures that, as it orbits around our planet, a different side must always be facing the direction of travel. Surely this leading side is likely to attract more hits and more powerful collisions than the opposite, trailing side. Is the Man-on-the-Moon's left ear therefore more pock-marked than his right? (Or the other way round).

Finally, why does the same side always face us. It's more than just because the moon revolves once for every orbit of the Earth! There must be a mechanism in place to keep it synchronised? I have a theory that, because of the reasons outline in the first paragraph above, the dark side of the moon is more susceptible to meteorite hits than it's sheltered near side and is therefore more cratered and weighs less than the near side which, as a result, would be pulled towards us by the Earth's gravity? That's a guess and almost certainly wrong so what is the real reason?


 

Offline RD

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If you look at a full moon it is completely pock-marked with craters. But here's what I don't understand: The near side of the moon always faces us. But surely the near side is shielded by The Earth, which is 3 or 4 time larger.

The Earth will draw fire from the moon, but not much because of the large Earth-Moon distance which is about thirty times Earth's diameter, this diagram is to scale ...



http://en.wikipedia.org/wiki/Moon#Orbit_and_relationship_to_Earth


so what is the real reason?

http://en.wikipedia.org/wiki/Tidal_locking
« Last Edit: 24/02/2009 01:22:25 by RD »
 

Offline LeeE

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I believe it's thought that both sides of the Moon were equally cratered but that the volcanic eruptions that produced the maria on the near side have covered many of them so that there are now more visible craters on the far side than the near side.
 

lyner

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What proportion of its life does the Moon spend being eclipsed from sunlight by the Earth? We're talking exactly the same proportion of screening from meteors / meteorites.
 

Offline John Chapman

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Hi Guys

Thanks for all that.

RD, I had no idea the moon was so far away. It seems amazing that there is such a stable equilibrium between the centrifugal force of the moons orbit and Earths gravity at that distance.

I'm not sure I fully understand the mechanism of tidal locking from the Wiki link. Is it that the Earth pulls a bulge on one side of the moon so that it is no longer perfectly round but slightly lopsided? The bulging side is then permanently pulled towards the Earth?

What about it having a leading side and a trailing side? Or are the speeds of asteroids, meteorites  and comets so great that this make little appreciable difference to the strike rates?

By the way, sorry to keep piling questions upon questions, but what's the difference between an asteroid, a meteorite and a comet?
 

Offline LeeE

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What proportion of its life does the Moon spend being eclipsed from sunlight by the Earth? We're talking exactly the same proportion of screening from meteors / meteorites.


I think it's probably even less than that because the meteors would have been coming from a greater number of directions.
 

lyner

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I guess you are right. The Earth, Moon and Sun are near to a plane so the Earth has a bigger chance of blocking Sunlight than if the Sun could be found anywhere over a full sphere. You could expect at least an order of magnitude in difference.
 

Offline Evie

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Asteroid: Any of numerous small celestial bodies that revolve around the sun, with orbits lying chiefly between Mars and Jupiter and characteristic diameters between a few and several hundred kilometers. Also called minor planet, planetoid.

Meteoroid: A solid body, moving in space, that is smaller than an asteroid and at least as large as a speck of dust.

Comet: A celestial body, observed only in that part of its orbit that is relatively close to the sun, having a head consisting of a solid nucleus surrounded by a nebulous coma up to 2.4 million kilometers (1.5 million miles) in diameter and an elongated curved vapor tail arising from the coma when sufficiently close to the sun. Comets are thought to consist chiefly of ammonia, methane, carbon dioxide, and water.

Definitions courtesy of The Free Dictionary.
 

Offline John Chapman

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Thanks for explaining that, Evie.
 

Offline dadismaster 420

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Lets start with why the emoon always faces earth. the moon was split from the earth a long time ago by an astroid. debree was stuck in orbit w the earth after the collision. the astroid caused the earth and the debree to rotate at the same pace. eventially the debree collected into todays moon. due to the debree of the astroid and the earth rotating at the same speed this caused tidal locking or the reason one side of the moon aleays faces the earth.

recently i just aced my physics class in college. bear with me on why the near side of the moon is more heavily cratered. Heres my best answer... as i stated the moon was formed from this debree. now once the moon was formed is was hot and molten. today the moon has cooled and became more solid. because of thr earths gravity the core of the moon was pulled towards the earth. this can only happen because of tidql locking or
 

Offline dadismaster 420

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Tidal locking is a way of saying that one side of the moon always faces earth. all in all the moons core is located closer to the earth. it is not perfectly centered so when asteriods hit the moon on the near side in acient times lava could rush and form these visible dark spots. on the far side of the moon the crust is extreamly think so no dark spot could be formed.

hope this clears up some mind boggling questions post back for questions or further explinantion
 

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