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whiteliondreams's avatar

How does the moon, based on it's size and weight, orbit the Earth when the Earth has relatively weak gravity?

Asked by whiteliondreams (1717points) August 8th, 2012

I don’t know if what I am asking is relative or ignorant, but I am curious to know based on what scientists said in Houston: “the Moon rang like a bell”.

One theory claims that the Moon was a part of Earth and it was chunked off from a collision.

Another theory claims that the Moon is hollow.

Another theory is that the Moon is an extraterrestrial craft.

Finally, there is a theory that the Moon isn’t real at all.

Has anyone heard or read about this? I’m not a David Ecke fan, but a point was brought up on his behalf that I have not confirmed because I am not savvy on the lines of physics.

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22 Answers

Mr_Paradox's avatar

The moon is in the exact right area to be captured by the Earths gravity. Not to close and not to far. Well it actualy IS a little too close. The moon is in a slightly degrading orbit. It should hit the Earth in about another 100 billion years. I’m personaly a fan of the theory that the moon was a slow moving asteroid that we captured in our gravity well. That would explain it’s orbit because something that is ejected from the Earth doesn’t establish orbit by itself. It needs an outside force.

jrpowell's avatar

The theory that something banged into the earth and knocked off chunks that coalesced and formed the moon is the most common and accepted. And it makes sense since there isn’t very much iron on the moon. Compared to the amount of iron in the earths core there is very little on the surface of our planet.

And like Mr_Paradox says, the moon gets closer to us every single day.

We were just lucky things worked out the way they did.

ragingloli's avatar

Actually, the moon is moving away from Earth, not getting closer.

Also, please do not use the word theory for the ridiculous musings of crackpots.
A theory is an explanatory framework to explain known facts, and that is backed up by a large amount of evidence.
Neither the “hollow moon”, “moon is a spaceship” nor the “moon is a hoax” fairy tales have any evidence at all.

jrpowell's avatar

Loli is correct, I was wrong.

Qingu's avatar

It’s actually pretty well accepted (but not considered proven) that the moon was created out of the ejecta that resulted from a Mars-sized object smashing into Earth billions of years ago. Giant impact hypothesis

As for “why does the moon orbit Earth,” this hasn’t been a mystery for, oh, more than 300 years? Newton’s laws explain the gravitational attraction between the Earth and the moon. Are you asking why Newton’s laws are true?

gasman's avatar

First, we know it isn’t hollow. The moon “rang like a bell” in the sense that a small seismic event (rocket impact) generated resonant oscillations in the moon’s crust detectable by lunar seismometers. The notion that the Moon is hollow sounds like a variation of hollow Earth theories, a crank science on a par with the flat Earth hypothesis.

The moon is indeed getting farther away, by a whopping 38 millimeters per year (ref). Way in the future, all solar eclipses will be annular – goodbye Bailey’s beads.

As for the giant impact hypothesis ( <—Wikipedia link) here’s what the Planetary Science Institute has to say about the origin of the Moon:

…the giant impact hypothesis continues to be the leading hypothesis on how the moon formed. Is it right? Can it be disproven by more careful research? Only time will tell, but so far it has stood up to 25 years of scrutiny.

Mr_Paradox's avatar

@Qingu If the moon was just ejected strata the it would have just left the Earths gravity well. There is no way to add the momentum nessasary to start orbit. Even if the moon didn’t leave the gravity well it would be in geosynchronous orbit.

BhacSsylan's avatar

So, I actually don’t know too much about this per se, far less then those already commenting, but I had to make one comment. @Mr_Paradox, do you think it’s very likely that the leading theory for the last 25 years has a flaw as serious as that? As noted, it could be wrong, but I think that’s a pretty huge thing to miss.

[edit] also, the Wiki mentions the orbit of the moon at least twice from a cursory glance, once mentioning that the direction of earth’s spin and the moon’s orbit is used as evidence, and once saying that “Impact conditions can be found that… satisfy the angular momentum constraints of the Earth–Moon system.” So if anything, that sounds like the current orbit supports this theory.

whiteliondreams's avatar

@Qingu No, not questioning Newton’s laws, I am asking if the Earth has a weak gravitational pull, how does the Moon orbit the planet when it exceeds Earth’s gravitational pull? In other words, the Moon is too big to be our ‘moon’ and it shouldn’t be there.

I’m not stating this as a fact, I am simply stating a notion expressed by David Icke and I want to know if there is an explanation or interpretation.

ragingloli's avatar

David Icke is the one that thinks that reptilian aliens have infiltrated society. He is a crackpot of the highest order.
Earth has a certain gravitational pull, the moon has a certain gravitational pull, and the moon’s orbit’s diametre is just right to keep its distance from Earth stable. The moon is not “too big”.
In actuality, were the moon smaller, and because of that would have less mass, it would, with the current orbit and velocity, be flung out into space, because the moon’s own gravitational pull would be reduced and earth would have less moon-mass to act upon.

whiteliondreams's avatar

@ragingloli Thank you, this is exactly the argument I am looking for. So, for instance, this disproves the hypothesis (that is what I should have used in place of theories) that the Moon is hollow. Yes? I know that in order for an object to have a certain pull, it should have mass.

Therefore, if the Moon is slowly pulling away from Earth as @gasman added, then the Moon should be a lot more heavier than a non-scientist can imagine. I actually read here where, ”Moonquakes detected by seismic sensors installed during the Apollo missions support the notion of recent activity on the moon, researchers added. All in all, the moon’s interior may still be hot.

If this is true, then a new set of hypothesis can rise or the impact theory can be supported further. In fact, I just remember reading an article that claimed that the Moon was a part of Earth based on the study of the objects collected from the Moon. I just can’t remember where. I did just find an article now from NASA that the Moon “possesses a solid, iron-rich core”.

One question for you though: Do you think David Icke is a crackpot because he believes in something you don’t? Or, is he a crackpot because you cannot fathom the idea that reptilian-like creatures live among us, so it makes no sense and it must be considered nonsense? I’m just asking.

Mr_Paradox's avatar

@BhacSsylan I’m just giving my point of view. It could be wrong, it could be right. I’m not going to force it on anybody.

Qingu's avatar

@Mr_Paradox, why would the ejecta leave Earth’s gravity well? I’m sure some of it did, but a large mass of it would have remained. We’ve seen the same thing happen on other planets. The impact would also explain the Earth-moon system’s very high angular momentum.

@whiteliondreams, again, I am not really sure what you are asking when you say “how does the Moon orbit the planet when it exceeds Earth’s gravitational pull?” It doesn’t exceed Earth’s gravitational pull. Also the moon’s gravity pulls back on Earth. Both bodies’ gravity are such that the orbit of the moon is mathematically explained by Newton’s laws almost perfectly.

Qingu's avatar

@whiteliondreams, David Icke is a crackpot because he believes in demonstrable nonsense.

BhacSsylan's avatar

@Mr_Paradox But it’s a point of view on objective facts. Your point of view can be tested, and apparently has been tested, since they know that angular momentum of the system is consistent with the hypothesis.

Mr_Paradox's avatar

@Qingu @BhacSsylan It just doesn’t add up for me. Nuf sed.

BhacSsylan's avatar

@Mr_Paradox So, you don’t have any hard reason to believe that? You just do? Okay…

whiteliondreams's avatar

I don’t like conflict over trying to reason. I am having this same issue on another posting and I really think we should be a little more tactful and considerate of people’s knowledge and opinions based on the fact that we know little about who we are conversing with. Just saying.

BhacSsylan's avatar

I have no problem with reason and debate. But one person saying ‘i have no reason to believe something, i just do’ does not a debate make. It produces no knowledge, and is useless to us who are trying to understand. If Mr. Paradox has a good reason for saying ‘it just doesn’t add up’, then fine, sure, it can be put out and debated. I prefaced my question with my lack of knowledge because really, i don’t know astrophysics, I’m a biochemist. Trying to understand much past the basics just of general relatively tends to tie my brain into knots. So if he had a reason for doubting it, I wanted to know why. If it was a good reason, awesome, we may learn something. If it’s not, then the others around who understand the physics can explain why it’s not (like what is already going on about the ideas you started the question with), and again we all learn something.

But just saying “i don’t believe it, because”. Is not an all helpful. Especially on a site based around answering questions.

gasman's avatar

Can we prove that the Moon isn’t hollow? (Cornell University). This article lays out several lines of evidence:

…the large-scale gravitational field of a planet does not convey any information about the (radial) distribution of mass. Nevertheless, if a hollow Moon is assumed, the lunar density would have to be un-physically large to generate the observed gravitational field.

Furthermore, fine-scale variation (e.g., variation along the orbit of the Lunar Prospector orbiter) of the lunar gravitational field is consistent with geologic processes involving a crust, mantle, and core.

…the moment of inertia parameters indicate that the core of the moon is both dense and small, with the rest of the moon consisting of material with nearly-constant density.

The lunar seismic data have helped constrain the thickness of the crust (~45 km (30 miles)) and mantle, as well as the core radius (~350 km (220 miles)).
@whiteliondreams Wouldn’t you call this compelling evidence against the Moon being hollow, especially with no credible evidence to support the claim?

whiteliondreams's avatar

@gasman Yes, aside from the article I read at NASA. Thank you.

mattbrowne's avatar

There are even tiny asteroids with moons and they have super-tiny gravity. Gravity is gravity. When you stand close to your girlfriend your gravity is pulling at her and vice versa. Only dry friction keeps you apart.

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