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Moon's Bulge Explained

Zonk posted more than 7 years ago | from the put-some-cream-on-that dept.

204

anthemaniac writes "The moon has an unexplained bulge that astronomers have been trying to find a source for since 1799. Finally, an apparent answer: The equatorial bulge developed back when the developing moon was like molasses (and you thought it was cheese!) and, rather than today's nearly circular orbit, it 'moved in an eccentric oval-shaped orbit 100 million years after its violent formation.'"

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204 comments

no (5, Funny)

GigsVT (208848) | more than 7 years ago | (#15843550)

It's just happy to see you.

no-A moon with a view. (0)

Anonymous Coward | more than 7 years ago | (#15843606)

[Insert 'mooning' your girlfriend joke here]

Re:no (0)

Anonymous Coward | more than 7 years ago | (#15843615)

I actually went to the linked article and got a bulge from the MSN adds. Wow, something my corporate internet does not block! What constitutes "porn" is relative I guess.

Eccentric vs. Circular Orbit (1)

TrisexualPuppy (976893) | more than 7 years ago | (#15843980)

Circular orbits are the lowest energy state. Thus, tidal forces cause the system to gradually lose energy until it settles into a circular orbit. When you add up the 1/r potential of gravity and the repulsive 1/r^2 centrifugal potential, you get a function with a nice minimum which is the radius of a circular orbit. The reason that elliptical orbits occur is because the period of the orbit exactly matches the period of oscillations around the minimum potential. Thus when you go around once, you end up right back where you started and get a closed, elliptical orbit. (Note that this is true only for Newtonian mechanics. Once you take General Relativity into account, the periods aren't the same and orbits precess. We can directly observe this in the orbit of Mercury as a perhelion shift of 43 arcseconds/century.)

Re:Eccentric vs. Circular Orbit (3, Informative)

Anonymous Coward | more than 7 years ago | (#15844296)

While you have a very interesting theory, I think it is more likely due to the fact that circular orbits are the lowest energy state. Thus, tidal forces cause the system to gradually lose energy until it settles into a circular orbit. When you add up the 1/r potential of gravity and the repulsive 1/r^2 centrifugal potential, you get a function with a nice minimum which is the radius of a circular orbit. The reason that elliptical orbits occur is because the period of the orbit exactly matches the period of oscillations around the minimum potential. Thus when you go around once, you end up right back where you started and get a closed, elliptical orbit. (Note that this is true only for Newtonian mechanics. Once you take General Relativity into account, the periods aren't the same and orbits precess. We can directly observe this in the orbit of Mercury as a perhelion shift of 43 arcseconds/century.) . . . more or less.

Well (2, Insightful)

styryx (952942) | more than 7 years ago | (#15843556)

Hey, way to suck the fun out of this with 'the cheese' joke in the description.

Re:Well (0, Redundant)

Tackhead (54550) | more than 7 years ago | (#15843611)

> Hey, way to suck the fun out of this with 'the cheese' joke in the description.

No kidding. Everyone knows the real reason for the bulge is because Ballmer threw a chair at it. The side that got hit is indented in the form of the letters "CHA"...

Uh huh (4, Funny)

Anonymous Coward | more than 7 years ago | (#15843557)

Its nothing more than a little baby fat.

You know you're old when... (0)

Anonymous Coward | more than 7 years ago | (#15843560)

""The moon has an unexplained bulge that astronomers have been trying to find a source for since 1799."

Well there goes the middle-age spread excuse.

---
It's been 20 minutes since you last successfully posted a comment-and that hasn't stopped me yet, Taco.

Wait a minute... (2, Insightful)

The Real Toad King (981874) | more than 7 years ago | (#15843564)

Don't all circular/spherical objects bulge around the middle? take this o for example. The middle part of it is wide at the middle, and short at the top and bottom.

Re:Wait a minute... (3, Informative)

Kelson (129150) | more than 7 years ago | (#15843711)

The radius at the equator is slightly longer than the radius at the poles. It's not quite a perfect sphere.* Sort of like if you took a rubber ball, set it on the floor, then pushed down slightly.

The same is true of the Earth, though I believe it's generally attributed to the Earth's rotation.

* Yes, I know that craters and such interfere with it being a perfect sphere too. No need to get pedantic, people of Slashdot. Well, no more than usual.

Re:Wait a minute... (4, Insightful)

Mr. Underbridge (666784) | more than 7 years ago | (#15843962)

Right. I'd assume these guys accounted for the tendency of a rotating body to form an oblate spheroid, and that the moon's current orbit can't account for the degree of its oblacity (if that's a word). Thus it would need to have exhibited some more violent orbit in the past.

Re:Wait a minute... (1)

eggoeater (704775) | more than 7 years ago | (#15844012)

IANACosmologist/Astronomer...but I think you can explain the Earth's bulge because it is still active;i.e. is not solid so it can expand here, contract there, sorta like a water balloon. The moon is probably completely solid and therefore should not bulge.

Like a dinosaur (4, Funny)

Namarrgon (105036) | more than 7 years ago | (#15843731)

It's thin at one end, much much thicker in the middle, and thin again at the other end.

I have another theory, you know...

Re:Wait a minute... (4, Insightful)

Billosaur (927319) | more than 7 years ago | (#15844107)

Don't all circular/spherical objects bulge around the middle?

If they are planets and they are spinning, yes. Just look at pics of the Jovian worlds, especially Saturn. And the Sun has a definite bulge. Of course, for most of the planets, the bulge is pronounced because they are still elastic to some degree. The Earth bulges owing to the fact that the continents are riding around on their crustal plates, which ooze on molten material, and the Moon is tugging on them as it goes aroudn us. The Moon's is more fascinating because it is a geologically dead world, so the bulge happened some time in the past and then got frozen in place.

Come on people, give the moon a break... (5, Funny)

Bamafan77 (565893) | more than 7 years ago | (#15843568)

Everyone knows your metabolism slows down after a certain age. Still though, a half hour a day on the treadmill probably wouldn't hurt either.

Re:Come on people, give the moon a break... (5, Funny)

Anonymous Coward | more than 7 years ago | (#15843583)

30 minutes a day on the treadmill? The fucker goes 1km/sec ALL DAY LONG!

YOU do that, fat-ass!

Re:Come on people, give the moon a break... (1)

cagle_.25 (715952) | more than 7 years ago | (#15843858)

While losing no energy, at that (except for the whole 'tides' thing).

Re:Come on people, give the moon a break... (1)

Joebert (946227) | more than 7 years ago | (#15843601)

Still though, a half hour a day on the treadmill probably wouldn't hurt either.

Oh yeah, I see you orbiting around the earth 24 hours a day 365 days a year, 366 on leapyears, you have plenty of room to talk.

Re:Come on people, give the moon a break... (1)

Bamafan77 (565893) | more than 7 years ago | (#15843670)

Oh yeah, I see you orbiting around the earth 24 hours a day 365 days a year, 366 on leapyears, you have plenty of room to talk.
No one is asking the moon to be a workaholic. I know everyone expects her to be Super Moon, but she needs to say "No" every once in a while and take some "me time". Just look what happened to the moon in the opening sequence of "Thundarr the Barbarian". Take heed, moon, take heed.

(Wait, the moon IS a chick, isn't it?)

Re:Come on people, give the moon a break... (1)

Joebert (946227) | more than 7 years ago | (#15843709)

Wait, the moon IS a chick, isn't it?

Do you feel like you're in the back of a Range Rover, with Jack Nickelson driving, & Woody Harrelson in the back seat with you ?

Re:Come on people, give the moon a break... (1)

smart.id (264791) | more than 7 years ago | (#15843738)

Wow, an obscure Anger Management reference. However, what the hell did it have to do with your parent poster?

Re:Come on people, give the moon a break... (5, Informative)

isellmacs (661604) | more than 7 years ago | (#15843739)

http://en.wikipedia.org/wiki/Luna_(moon) [wikipedia.org]

http://en.wikipedia.org/wiki/Selene [wikipedia.org]

I'd say "Her" would be appropriate, as the name Luna (the name of our moon) comes from the Roman Goddess of the Moon.

Re:Come on people, give the moon a break... (2, Interesting)

Saint Stephen (19450) | more than 7 years ago | (#15843823)

In Tolkien the Sun was the woman and the Moon was the man, always seeking her brilliance ... and occasionally wandering into the sky with her, only to be burned terribly.

I always found that mythology better.

The sun is a woman, and the moon loves her!

Re:Come on people, give the moon a break... (1)

LordP (96602) | more than 7 years ago | (#15844039)

So that must mean she's "retaining water" (instead of beer).

Re:Come on people, give the moon a break... (4, Funny)

19thNervousBreakdown (768619) | more than 7 years ago | (#15844063)

(Wait, the moon IS a chick, isn't it?)

Hmm. So beautiful it inspires poetry, so attractive it pulls the sea, and men feel compelled to spend more than they can afford just to walk all over it. Oh, and let's not forget, every 28 days it swells and causes dogs to howl.

I think you're on the right track.

Re:Come on people, give the moon a break... (1)

Tony Hoyle (11698) | more than 7 years ago | (#15843737)

Orbitings easy - you just have to fall towards the ground and miss.

It's *not* orbiting that's the hard bit.

Re:Come on people, give the moon a break... (1)

Joebert (946227) | more than 7 years ago | (#15843791)

Orbitings easy - you just have to fall towards the ground and miss.

It's *not* orbiting that's the hard bit.

Anyone can get lucky & miss the ground sooner or later, it takes dedication to keep doing it.

The answer is apparent. (5, Funny)

BoBathan (166436) | more than 7 years ago | (#15843591)

Bulge at the equator, violent formation, clearly the Moon is American.

Re:The answer is apparent. (1)

Joebert (946227) | more than 7 years ago | (#15843676)

Bulge at the equator, violent formation, clearly the Moon is American.

Australian chicks figured that out after reading the first word.

Re:The answer is apparent. (0)

Lord Ender (156273) | more than 7 years ago | (#15844287)

No other country was started by violent revolution, no other country has overweight people, and this lame joke hasn't been overused to the point of absurdity.

May the mods have mercy on your witless soul.

Oblig... (2, Insightful)

Anonymous Coward | more than 7 years ago | (#15843593)

That's no moon...

Re:Oblig... (0)

Anonymous Coward | more than 7 years ago | (#15843640)

Oblig..? Really? I don't think so mister..

Re:Oblig... (0)

Anonymous Coward | more than 7 years ago | (#15843668)

You must be new here.

Re:Oblig... (0, Redundant)

Tim_sama (993132) | more than 7 years ago | (#15843716)

No, THESE are oblig: Yeah, but does it run Linux? Imagine a Beowulf cluster of these babies! In Soviet Russia, bulges moon YOU! I, for one, welcome our new bulging moon overlords...

Better than the last theory (0)

Anonymous Coward | more than 7 years ago | (#15843594)

I remember in High School the only theory they had was that something "very large" had impacted the moon while it was in development.

sometimes... things come to mind... (3, Funny)

CarnivoreMan (827905) | more than 7 years ago | (#15843610)

Well... perhaps the man in the moon was thinkin about some of them women from Venus....

Whatever (0)

Anonymous Coward | more than 7 years ago | (#15843627)

Yeh and our ancestors are monkeys.

But it is cheese! (0, Redundant)

cazbar (582875) | more than 7 years ago | (#15843642)

Just look at the Google map [google.com] (zoom all the way in).

Re:But it is cheese! (0)

Anonymous Coward | more than 7 years ago | (#15843726)

But like everything else google has, it's in beta. *me ducks* ;)

Monolith? (4, Funny)

wingfoot (769619) | more than 7 years ago | (#15843650)

There wouldn't happen to be a strong magnetic field at the bulge would there....? How about a black monolith buried beneath the surface causing the bulge....?

Re:Monolith? (1)

Brieeyebarr (938678) | more than 7 years ago | (#15843828)

Maybe. I guess if you want to know for sure you'll have to travel in time to the far off year 2001, I heard they were going to be excavating the moon around that time.

Missing energy (4, Interesting)

Harmonious Botch (921977) | more than 7 years ago | (#15843653)

So how did the eccentric orbit become so nearly circular? That takes a lot of energy ( and a little coincidence )

Re:Missing energy (5, Informative)

Jazzer_Techie (800432) | more than 7 years ago | (#15843719)

Actually, circular orbits are the lowest energy state. Thus, tidal forces cause the system to gradually lose energy until it settles into a circular orbit. When you add up the 1/r potential of gravity and the repulsive 1/r^2 centrifugal potential, you get a function with a nice minimum which is the radius of a circular orbit. The reason that elliptical orbits occur is because the period of the orbit exactly matches the period of oscillations around the minimum potential. Thus when you go around once, you end up right back where you started and get a closed, elliptical orbit. (Note that this is true only for Newtonian mechanics. Once you take General Relativity into account, the periods aren't the same and orbits precess. We can directly observe this in the orbit of Mercury as a perhelion shift of 43 arcseconds/century.)

Re:Missing energy (1, Funny)

frankyfranky (984895) | more than 7 years ago | (#15843772)

May I be the first to say...

What the fuck?

Re:Missing energy (1, Informative)

joeljkp (254783) | more than 7 years ago | (#15844108)

A more straightforward way of visualizing it may be to imagine a satellite around Earth in a highly elliptical orbit. At the nearest points to Earth, it's getting a little bit more resistance from the atmosphere, the magnetic field, etc. This extra resistance means it can't get as far out the next go-around, leading to a decrease in eccentricity, or a circularization of the orbit.

Re:Missing energy (3, Interesting)

gardyloo (512791) | more than 7 years ago | (#15844075)

Whoa. What's the repulsive 1/r^2 "centrifugal" potential? At first I thought you were including G.R. with the talk of tidal forces, but then I realized (via the 1/r potential) that you're talking about regular old Newtonian gravity. That's fine. But where's the repulsive potential?
      The only tidal forces I can see in this problem are evinced in the deformation of the earth or the moon, their atmospheres, and the ocean of the earth. Wikipedia has this to say about tidal locking:

There is a tendency for a moon to orient itself in the lowest energy configuration, with the heavy side facing the planet. Irregular shaped bodies will align their long axis to point towards the planet. Both cases are analogous to how a rounded floating object will orient itself with its heavy end downwards. In many cases this planet-facing hemisphere is visibly different from the rest of the moon's surface.

The orientation of the Earth's moon might be related to this process. The lunar maria are composed of basalt, which is heavier than the surrounding highland crust, and were formed on the side of the moon on which the crust is markedly thinner. The Earth-facing hemisphere contains all the large maria. The simple picture of the moon stabilising with its heavy side towards the Earth is incorrect, however, because the tidal locking occurred over a very short timescale of a thousand years or less, while the Maria formed much later.


    I'll have to try to work out how tidal forces within one astronomical body might lead to a circular orbit. It might be a well-known effect, but it's not obvious to me.

Re:Missing energy (1)

gardyloo (512791) | more than 7 years ago | (#15844128)

Ah. If you're talking about the pseudo-repulsive potential mentioned in the article (away from the barycenter), fine. BUT the sum of conservative potentials (as the 1/r and 1/r^2 ones are) is also conservative, and will STILL lead to elliptical orbits in general. So you've got to propose some non-conservative forces acting, and then you can't even really use "potential" in its usual sense of leading to a force via the gradient.

Since they're explaining bulges... (0)

Anonymous Coward | more than 7 years ago | (#15843674)

...maybe they can explain Brandon Routh's bulge in his Superman outfit. Scientifically that is.

It's quite simple actually... (2, Funny)

Anonymous Coward | more than 7 years ago | (#15843740)

It's where they covered up the "CHA" that Chairface Chippendale put there. They used a little too much moondust.

And now... (0)

Anonymous Coward | more than 7 years ago | (#15843741)

I can sleep in peace tonight...

OB Joke (0)

Anonymous Coward | more than 7 years ago | (#15843755)

----------- Cut here ----------

Every joke posted above this line are what flashed through your mind as you read the headline.

Gravity (1)

ModestMotorhead (954115) | more than 7 years ago | (#15843765)

Gravity is an amazing thing. On Earth we feel the pull of gravity constantly from the moon (tides). When the moon was more viscous it only goes to show that the Earth or other celestial bodies had some influence on the final shape of the moon.

moons bulge (-1, Redundant)

Anonymous Coward | more than 7 years ago | (#15843779)

caused by looking at uranus.

Moonbase (1)

winphreak (915766) | more than 7 years ago | (#15843813)

Well, here in a good amount of years, won't that bulge possibly be a base?

Re:Moonbase (0)

Anonymous Coward | more than 7 years ago | (#15844198)

As long as they are belong to us. All of your's, at least.

Duh! (0)

Anonymous Coward | more than 7 years ago | (#15843861)

Duh! After it slamed into the earth. Remember?

Enough already (2, Informative)

midkay (984862) | more than 7 years ago | (#15843915)

Isn't that enough of the "Because it's fat!" and "Because it's horny!" comments? If I knew how to mod all of you "Redundant", make no mistake, I would!

Re:Enough already (1)

thePowerOfGrayskull (905905) | more than 7 years ago | (#15844041)

Of course it's not enough. We all know the moon is fat and horny. It needs to take a quick orbit around the earth, then drift on over to the Sun to relieve some of that biological... erm... geological pressure.

Re:Enough already (1)

posterlogo (943853) | more than 7 years ago | (#15844081)

Sure, you're right, but with so much of the same lame jokes, shouldn't it have occured to some editor to not choose such a retarded article title?

Re:Enough already (0)

Anonymous Coward | more than 7 years ago | (#15844201)

Preggers?

medical emergency (0)

Anonymous Coward | more than 7 years ago | (#15843996)

Frickin' Viagra - if your bulge lasts more than 4 hours you are supposed to contact a physician immediately!!!

Make the moon a spaceship? (1)

mOdQuArK! (87332) | more than 7 years ago | (#15844022)

I wonder how fast you'd have to spin the Moon and how much you would have to hollow it to get a 1G environment on the inside of it?

Re:Make the moon a spaceship? (1)

Arker (91948) | more than 7 years ago | (#15844304)

Why on earth would you want to do that? Enjoy the low gravity instead. Give our overworked hearts a break. Strap on your wings and fly!

Flat Earth Scoiety (0)

Anonymous Coward | more than 7 years ago | (#15844034)

I wonder how they explain this one.

What does it say.... (0)

Anonymous Coward | more than 7 years ago | (#15844174)

What does it say about a person who notices the title of this article and immediately says "The moon has a penis?"

That's not a buldge, it is a feature! (1)

CodeMasterPhilzar (978639) | more than 7 years ago | (#15844283)

We here at Moon-Soft (tm) have warped the very shape of reality...er...this semi-spherical body. We can now provide longer vistas. Of course to fully take advantage of the improved horizons you'll need to upgrade your ship's thrust capacity, your visor's light filters... In fact, let me refer you to our friends over at Intele-spatial rockets. I'm sure they can outfit you with all the hardware you need to fully appreciate our development.

What's that? You prefer to keep your existing modest ship? Go where? Open-Orbit's space station? You say it is closer at hand, more affordable, and they even let you work on it if you'd like? What a preposterous idea! I'm sure they can't possibly offer you the same experience we have. Why, nearly everyone is going to the moon these days... Who'd want to stay in a closer, faster orbit?

Better explanation (0)

alshithead (981606) | more than 7 years ago | (#15844290)

I know where the bulge came from. The moon has been consuming massive amounts of cosmic beer. It's nothing more than a big beer belly folks!

How did Laplace find it? (2, Insightful)

helioquake (841463) | more than 7 years ago | (#15844301)

How did Laplace determine the existence of the bulge?

Was it a "simple" measurement of the shape of the Moon or something more sophisticated via his favorite mathematic tricks? Considering it is Laplace, he must have measured its eccentricity fairly accurately. I wonder what he used to do that in 1799.

Fondue (3, Funny)

fattybob (196045) | more than 7 years ago | (#15844334)

Mollases is more of a textural camparsion, but it must be remembered that this occured as the moon cooled, cooling from molten to solid cheese, so perhaps a better explanation would be that the bulge occured during cooling while the moon was like Fondue.

Oooh.... (0)

Anonymous Coward | more than 7 years ago | (#15844384)

...I like bulges!

-muppet
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