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Earth's Moon is a Rarity
Smivs writes "Scientists have concluded that moons like the Earth's are actually quite rare. Only 5-10% of planetary systems are likely to contain moons formed by planetary collisions. 'By the time the Earth's moon formed, when the Sun was 30 million years old, the planet formation process in our Solar System should have been approaching its end. In the latest study, Dr Gorlova's team looked at the heat signature of stars using the infrared. This allows astronomers to predict how much of that heat comes from the star itself and how much is re-emitted by dusty material encircling it.'"
What's also rarer is that OUR moon has a face on it. I don't see any other planets having moons with faces on them. So all these other loser planets just gotta admit that our moon is better than their moon.
Side note: In The End of Eternity, we developed time travel before space travel, and so never colonised the galaxy until we eventually discovered hyperspace in the 130,000th century and found that the galaxy was already full of other species and we had no room to expand. Eventually those from near the human extinction altered history to make sure time travel was not invented and thus ensure the expansion into a galactic empire. Apparently the idiots who wrote the sequel trilogy a few years ago failed to read this book (or Robots and Empire), and retcon'd the robots in as Eternals who killed off all competing intelligences in a bizarre and nonsensical addition.
I am TheRaven on Soylent News
And with us "our" moon? I smell a turkey!
Isn't this rather old news? I thought that it was already pretty well known that Luna is rather rare, as shown in the Rare Earth hypothesis?
How do they know the earth wasn't created by a collision with the moon? Cuz, the Earth does in fact revolve around the moon if you look at it that way and don't get all lazy with the math like those big slouches of history like Kepler did.
Equine Mammals Are Considerably Smaller
It amazes me that so many allegedly "educated" people have fallen so quickly and so hard for a fraudulent fabrication of such laughable proportions. The very idea that a gigantic ball of rock happens to orbit our planet, showing itself in neat, four-week cycles -- with the same side facing us all the time -- is ludicrous. Furthermore, it is an insult to common sense and a damnable affront to intellectual honesty and integrity. That people actually believe it is evidence that the liberals have wrested the last vestiges of control of our public school system from decent, God-fearing Americans (as if any further evidence was needed! Daddy's Roommate? God Almighty!)
.. the next time you're out in the backyard exercising your Second Amendment rights, the liberals will see it! These satellites are sensitive enough to tell the difference between a Colt .45 and a .38 Special! And when they detect you with a firearm, their computers cross-reference the address to figure out your name, and then an enormous database housed at Berkeley is updated with information about you.
Documentaries such as Enemy of the State have accurately portrayed the elaborate, byzantine network of surveillance satellites that the liberals have sent into space to spy on law-abiding Americans. Equipped with technology developed by Handgun Control, Inc., these satellites have the ability to detect firearms from hundreds of kilometers up. That's right, neighbors
Of course, this all works fine during the day, but what about at night? Even the liberals can't control the rotation of the Earth to prevent nightfall from setting in (only Joshua was able to ask for that particular favor!) That's where the "moon" comes in. Powered by nuclear reactors, the "moon" is nothing more than an enormous balloon, emitting trillions of candlepower of gun-revealing light. Piloted by key members of the liberal community, the "moon" is strategically moved across the country, pointing out those who dare to make use of their God-given rights at night!
Yes, I know this probably sounds paranoid and preposterous, but consider this. Despite what the revisionist historians tell you, there is no mention of the "moon" anywhere in literature or historical documents -- anywhere -- before 1950. That is when it was initially launched. When President Josef Kennedy, at the State of the Union address, proclaimed "We choose to go to the moon", he may as well have said "We choose to go to the weather balloon." The subsequent faking of a "moon" landing on national TV was the first step in a long history of the erosion of our constitutional rights by leftists in this country. No longer can we hide from our government when the sun goes down.
And with us "our" moon?
That's no moon. and you're on Alderaan. buckle up.
The theory of relativity doesn't work right in Arkansas.
if you assume that in the universe a planet or even a natural satelite is more than a grain of sand on this cosmic beach.
Not only are moons rare, but earth's moon is actually the fifth largest in our solar system. Considering how small our planet is and how big our moon is, I would say it's probably extremely rare to find similarities like this in the universe.
Full Tilt
I suggest you learn how to use these if you want anyone to actually attempt to read your drivel.
Seven puppies were harmed during the making of this post.
Bunch of lunatics.
Science advances one funeral at a time- Max Planck
The originators of the Rare Earth hypothesis made an assumption that large moons around rocky planets would be rare. The news item tends to support their assumption.
I thought it wasn't all that established that Luna was created from Tellus. According to the article it makes that assumption... How strange.
There is only one of it.
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Theres 200 people in the room..10 to 20 of them have a birthmark on their left cheek... how RARE.
Theres 2000 people in the room..100 to 200 of them have a birthmark on their left cheek... how RARE.
Given distances between galaxies 5 to 10 percent seems rare, but if distance didn't matter then this percentage is hardly RARE considering the vastness of the universe, and number of galaxies.
waiting for ad.doubleclick.net
The diameter of the Moon is 70% of that of Mercury and about a third larger than Pluto. The Earth and Moon arguably form a binary planetary system.
Our particular arrangement--a single moon with a geosynchronous orbit and a certain distance--is one of who knows how many possible configurations. We wouldn't speculate on how it's unusual to have any other arbitrary setup. Is there anything unusually notable about our Moon, from an independent viewpoint?
do not a lambchop make.
To be honest, I'm not convinced that you can take a SF plot device and run away with it too far in the real world.
1. Radiation. Actually, Earth probably has the least radiation problem in the solar system, because of its strong magnetic field.
Venus, for example, started extremely similar to Earth but was doomed because its dynamo stopped (and was probably weaker to start with). So the solar wind stripped away all hydrogen, leaving it with an atmosphere of CO2.
Mars hardly has a dynamo because its core froze already. Fat lot of good it did for intelligent life there.
Mercury. Ditto. Its magnetic field is at a whole 0.1% of Earths.
So even when you factor in the different mass and conditions, it seems to me like Earth is unique in having too _strong_ shielding, not in needing some plot device to weaken it.
2. (Or 1a.) If allowing more radiation in was better, you don't need a moon for that. Just rotate slower.
(And indeed the way I remember it, the collision theory says that the same collision that created the moon actually accelerated Earth's rotation a lot.)
Or lose your water, which stops plate tectonics, which kills off the dynamo. Easy.
In fact, you need a whole bunch of special conditions to _keep_ your shielding. Losing it seems more like the norm for a rocky planet in the right band to not turn into a snowball. If the moon's positive influence were punching a hole in our shield... heh... then a lot of planets would get there without a moon just as well.
3. Mutations. Longer text, so have patience please.
Well, this is stuff that happens anyway, simply because some UV gets through, there are radioactive elements in the soil, and even because simply errors happen when transcribing DNA. Especially look again at the last parts: even if you kept something under a slab of lead, without UV or cosmic radiation at all, it would still mutate.
Most of the history of life (except for virii, some bacteria and your immune system) was about _preventing_ mutations. Your cells have layers upon layers of defenses against that kind of thing. Starting with the very fact that you're DNA instead of RNA based, and all the repair proteins, and it goes on and on.
Heck, even the fact that you age is a defense against cancer, i.e., against mutation. Your cells start with a max division counter and literally count divisions. So if that mechanism didn't break down too, a tumour would reach a maximum size and stop. Unfortunately that also means that as more and more of your cells reach that limit natuarally, there's more and more damage which can't be repaired, and you discover the fun of old age.
At any rate, any multi-cellular kind of life, actively fights off mutations. Simply because you can't exceed a certain complexity without preventing mutations. You can't have a body consisting of gazillions of cells, if they don't obey the rules. If cells in your palm randomly tried to evolve into a nose, your left foot tried to become a palm, etc, your body would break apart pretty fast.
You also have to understand that this all happens on a "good enough" basis. Your body could evolve even more fool-proof defenses -- and through the billions of years it has, slowly -- but beyond a point they wouldn't be worth the extra complexity and energy requirements. Plus, in the long term, perfect repairs would also mean an inability to evolve. So anything that got too good at it just disappeared later in the next glaciation, when it was unable to evolve.
And in rare cases, even conversely: if it's of advantage to mutate faster (if still in a controlled manner), mechanisms evolve to create just that. E.g., there are cells in your immune system which actively mutate certain genes randomly, to try to produce a protein that exactly matches a target protein. (E.g., a piece of a new virus's capsid.) There's literally an enzyme in there whose sole role is to junk a random codon (think: byte) of DNA, so the repairs would kick in and some of them would get i
A polar bear is a cartesian bear after a coordinate transform.
Of course it's a rarity, there's only one moon belonging to the Earth.
As you probably know, Asimov wrote not only fiction, but non-fiction for the masses, and was rightly well-known for the way in which he made science not just understandable but interesting. He explained in a number of works, including The Tragedy Of The Moon, explaining how unique the moon is.
As noted in the parent post, Asimov will often incorporate real science into his fiction.
So, what's this about how the Earth's moon is unique? Is this something new?
404555974007725459910684486621289147856453481154 in hex is "You sank my Battleship?"
[GPG key in journal]
That is the theory most have heard.
Of course, it could be that the moon was moved into position
in order to make the planet more stable for future use.
You are being MICROattacked, from various angles, in a SOFT manner.
M O O N, That spells moon - Tom Cullen
So potentially 2/9 so far...
Maybe proportionately large moons are rare, but perhaps not double planets. The study only looked for dust from smash-ups. But what if a second body somehow enters in joint orbit with a planet without smashing into it first? It wouldn't show up in that study. But, the orbital mechanics to pull that off may be tricky. Something to think about.
Table-ized A.I.
the Moon will fly off into space, so a similar Earth/Moon combo will be even rarer.
As for the unconfirmed theory that the Moon was created by an impact on Earth, I've always wondered what happened to the impacting object... any theories on that?
Your post was actually scary. Not in the way you meant it to be though. I hope English is not a language you use often (in which case, kudos for trying, but don't learn the language from pop-culture movies ;-). If you are accustomed to speaking/writing English, and you are not a spam-bot, go get medical help from a qualified medical professional.
Or, is this some really off the shore acid-trip based sarcasm?
I'd love to see the cows which produced all that milk... ;)
- passion
. we have been not lucky about Earth's satellites, but... just imagine that we have MANY moons running around the Earth... like in this unique Flash animation: http://www.ghostnasa.com/posts/014manymoons.html it shows (also) how exoearths (with many satellites) could look .
http://www.ghostnasa.com/ http://www.gaetanomarano.it/articles/articles.htm
Earth and Pluto are similar in having a moon which is a decent fraction of their own mass. The two moons of Mars, and the moons of the four gas giant planets are minute in comparision to their primary bodies.
Earth and Pluto are sometimes called binary planets for this reason. And there is no easy way to show how they formed in this way, other than invoking chance impacts shortly after formation.
http://michaelsmith.id.au
Interesting, I would expect the Earth and the Moon to revolve around a common center of mass which in turn revolves around the apotex you mention. I guess that the Moon orbiting the Earth is a myth, after all.
We only recently discovered/observed a star system with 5 planets, and made a big stink (and I'm sure it's deserved). We see stars, but we are not even "seeing the surface" when it comes to planets. Given these, should the researchers be so confident/bold to make such claims? I'd thought astronomy/astrophysics are a bit more respectable discipline than, say, literary theory or political science?
Since there are no -1: misinformation in the comment system, I instead reply to your post with wikipedia's article.
Antiope
Orbit of the Moon
Barycenter(Centre of mass)
The originators of the Rare Earth hypothesis made an assumption that large moons around rocky planets would be rare. The news item tends to support their assumption.
If I remember correctly, they claimed that without a large moon, Earth's rotational angle would wobble wildly at times and a single pole would point toward the sun all year round for millions of years, like Uranus. (Recent research suggests that Mars has done this in the past.) This allegedly would slow the formation of life.
I don't see how this would be significant, though. There would still be places with the right temperature for life, and perhaps some that are even fairly stable because they always face the sun at the same angle. Earth went through fairly wide swings also. Roughly 200 million years before the Cambrian Explosion, the Earth was possibly almost completely covered in thick ice, slowing the metabolic rate of any life. A "pole pointer" planet would at least have a warm spot at or around the sun-facing pole. Thus, it may be a wash.
There's a similar question for tidally-locked (same face) planets around smaller stars. Such stars burn longer, giving life a longer chance. However, they are also more radioactive at a comparable distance. Small stars are far more common than mid-sized sun-like stars, so if complex life can form and survive on a tidally-locked planet with more radiation, there's an issue about whether SETI etc. should also look at these smallies.
The problem is that Earth is our only source to compare so far. We don't really know all the viable life-forming planet configurations.
Table-ized A.I.
I'm still skeptical about astrophysics findings in general, seeing as we were wrong about the oxygen content of our own star.
Why not focus on being exact within our own solar system, before we venture farther?
Just -1, Troll talking to another.
The Earth doesn't revolve around the moon, and the moon doesn't revolve around Earth. They actually both revolve around a point that astronomers call the apotex, which lies about 187 million miles from Earth.
Whoever modded that informative didn't get whatever there was to understand about this comment anyways (nothing I guess? Even Google doesn't know what's an apotex). Seriously tho, the GP is wrong in that the Earth and the Moon revolve around their barycentre, which is if I recall correctly a little bit above Earth's surface.
You just got troll'd!
Rare? Okay. Too bad that the moon actually slowed the creation of life with its meddling gravitational pull. Without the moon interference amino acids would have formed earlier and we would have the holodeck and Duke Nukem Forever by now.
The last article is the most important...the point that the Earth and Moon orbit around is beneath Earth's surface. Who are the idiots modding up the GP? Apotex is a Canadian pharmaceutical company, of all things.
They actually both revolve around a point that astronomers call the apotex, which lies about 187 million miles from Earth.
If I remember correctly, the center which they both orbit around is *inside* the Earth (but not at the center). Some have suggested that the difference between "moon" and "double planet" could be defined by whether the center of gravity is inside the larger body or on the outside (between them).
Table-ized A.I.
The moon isn't just a rarity in terms of formation. It's also a rarity in terms of fortune, I think. How awesome is it that there's a big ball of rock only 200,000 miles away where we can practice our space technology on till kingdom come? How awesome is it that it has enough gravity (and water!) to make a moon base possible? I think in the next 5000 years, we'll look up at the moon and see next year's resort spa trip. Though it's a huge, lucky win, we also kind of got screwed by being so far from the next nearest star.
Sorry. Just another example of the vast conspiracy arrayed against Neocons by the infernal liberals.
Obviously, the Giant Space Mouse roams the universe, looking for tasty large moons (since they are made of cheese). That's why our moon is a rarity. When the Giant Space Mouse came for it, the Fantastic Four used the Ultimate Nullifier or some Giant Space Cat to take care of it. I bet Wolverine was involved, too, since he's ALWAYS involved.
Anyhow, that's why our moon and its delicious Swiss Cheese core are still around, while other planets with their lame Brie-mantled moons were pillaged by the Giant Space Mouse.
Vincent J. Murphy
Spandex Justice
The time travel became the ultimate 'nanny state' system, life became static. Apparently the plot is trying to show that either you can have time travel or space travel but not both (hey Heisenberg fans, see a parallel?)
Any development that lead to space travel discovery was prevented by time-cops on purpose, because those developments caused various unpleasant situations - people died, or economy crashed or whatever, basically major catastrophes in the eyes of the time-law. That was the point of time travel and that was THE ONLY point of time travel. Only time-cops were allowed to travel and only for the sake of observing and changing events in order to preserve a static Earth.
In fact the 130,000th century tried to block itself from time traveling cops of the previous centuries, so that they would not be able to observe what happens in the future so that they would not modify the past enough for the 130,000th century not to be able to create space travel.
In any case, the people in the 130,000th century were pissed off that when they finally have invented the space travel, they discovered that there is nowhere to go.
You can't handle the truth.
ååååéðfßfðgfðgfß fkjopijp ðßkókköököøøøkójókjííé qäwwåáasdfßa
FUCKYOU
smelly Re:Scientists talking about the moon?!?
Hu? Are you being sarcastic? From what I can acknowledge as sensible theories it could have been formed by an impact or it could have been formed from lumping together materia like planet(oid) and surely large satellites plausibly could form. Or?
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Not that I'm in the field, but I can't say I've heard of Earth being called a binary planet.
The centre of gravity of Pluto and its moon is somewhere between the two, so that I can understand is binary. But Earth and our moon? I'm pretty sure the centre of gravity is well beneath Earth's surface.
tl;dr version: could you provide a reference?
- RG>
Hey pal, this isn't a pleasantforest, so don't waste my time with pleasantries!
What a funny troll. I guess it shows that people will believe anything as long as it's said/written in an authoritative manner.
187 million miles. Hmm, is there ANYTHING of note 187 million miles from the Earth, other than the other side of its orbit around the Sun?
There are two kinds of people: 1) those who start arrays with one and 1) those who start them with zero.
The amazing thing, to me, is that the Moon's diameter as viewed from the Earth is almost exactly the same as that of the Sun. I've heard that, of the moons in the Solar System, only a handful subtend the same arc as the Sun when viewed from their primary's surface (though of course "surface" is a tricky concept when we're talking about the gas giants), and of those, I don't think many of them are spherical. The kind of diamond rings we get during eclipses are probably quite rare.
It's Carl Sagan's g-g-g-ghost!!! [/me runs and hides]
Blank until
IMBO, the earth-moon system can still be called a binary planet as no other major body in the solar system except Pluto has a satellite with as large a mass fraction as the moon is to earth.
And we're back to the moon allowing complex life.
Plot device vindicated. In all of one short line of text.
Earths core is solid, probably nickel and iron.
You're demonstrably wrong. In all of one short line of text.
It is no longer uncommon to be uncommon.
watch your language, you lunatics!
Can you answer this question? How can the moon have only about 1/80 of earth's mass, but have almost 1/6 the gravity? I would think gravity would be linearly proportional to mass.
This ad space for rent.
Ttile should be "Earths moon is an odd ball."
All the other planets have Space Stations.
Are you serious, or are you trolling?
For this you need Newtons law of Universal Gravity. The formula you want is right there. As you see, there two masses, and one radius. Let's assume we have a mass of 1kg on the surface of earth (and later on the moon), that's our m2 and as such we can ignore it the whole calculation.
Some data about Earth:
Some data about The Moon:
The gravitational constant G = 6.67x10^-11 N m^2 kg^2. The formula we are going to use is F = G * m1 *m2 / r^2. We calculate the force exerced on an object on the surface of the stellar body, so we need to take its radius, because the center of gravity of the stellar body is well, in it's center.
So, first for Earth: F = ( 6.67x10^-11 * 5.9736x10^24 * 1 ) / ( 6371000 ^2 ) = 9.81 N
Now, the moon Earth: F = ( 6.67x10^-11 * 7.3477x10^22 * 1 ) / ( 1737100 ^2 ) = 1.62 N
So, as you can see the force exerced on a body of 1kg on the surface of the Moon is only 1/6 of the same object on the surface of Earth. Yet, as you can see, Earth has 80x the mass of the Moon. What did you ignore? The radius! That one has an even greater effect on gravity than the mass: it is a inverse square law.
You do realise that this is middle-school physics, don't you?
Ahhh...the great dumpster continuum. Many a free computer will be found there. -- sowth (748135)
--
Reverse outsourcing: it's the future
How is 5-10% "quite rare"? It's the same order of the magnitude...
I do not believe in karma. "Funny"=-6. Do good and forbid evil. Yours, Oft-Offtopic Flamebaiting Troll.
The orbits of the earth and moon are both concave relative to the sun. From an outside view, they both orbit the sun, but the moon wiggles a bit during its solar orbit. The orbits of small moons of planets are convex wrt the sun for part of their orbit.
You're quite right : If you compared the force of the Earth's and Moon's gravity from (say) a million miles away, the earth's would be 80x that of the moon.
but you mean the gravity at the planet's surface and although gravity goes up linearly with mass, it goes down with the square of your distance from the centre of mass. So, the earth has 80 times the mass of the moon but you're about 4 times further away from the centre - so you multiply by 80 and divide by 4x4 => 5 times the gravity (or 6 if you use more accurate figures).
Think about this the next time you watch a Sci-Fi movie in which an interstellar starship gets dragged off course by a black hole: from several A.U. away the gravity will be no different than a large star - all that jazz about wobbly visual effects, sphaghettification, theramin music, mystical visions of hell and time slowing down (or, in a more pedestrian universe, getting torn apart and turned into a brief x-ray fart) only happens when you get much closer to the centre than the surface of any reasonable star would be.
In a survey of 100 programmers, 111111 thought that duck-typing was a good idea.
The moon has been around for a far longer period of time than the human race. Isn't it more reasonable to assume that the human menstrual cycle closely matches that of the moon?
The saddest poem
Yeah, I've often thought that if one wanted to look for alien tourists the best place to do so would be in the path of a total solar eclipse. Not only is the earth's moon probably rare'ish, but it's also fortuitously at the right apparent size at the moment to produce one - the moon does migrate in it's orbit and so the window for this to happen is quite small on a geological timescale (a few million years).
:-)
Of course any space-fairing alien could see a total eclipse at any time by positioning their spaceship accordingly, but so see one on a planets surface where there is there is atmosphere and complex life to react would not be common. In fact I'd go look at the point of maximum totality and duration.
It's real hard to guess how rare the earth/moon/eclipse/life combination is, but current figures would suggest we probably have to only such combination within several thousand light years. We're probably on some magazine list in the Epsilon Eridani IV library as '10 things to see before you die'
If there was another star too close to us, that would be much, much worse than not having a moon at all. However I agree 100% with the rest of your post.... :)
I hold very few opinions. I hold information based on observation and fact. If you wish to disagree, please use facts.
It's not a "comment system". It's a moderation system. The comment system is what I'm using to write this. The moderation system is to promote quality posts. Personally I thought it was funny, and the GP was absolutely hilarious but oh well.
Equine Mammals Are Considerably Smaller
I love the theories swirling around this word.
Carry on.
I am very small, utmostly microscopic.
Everyone knows that the moon is really a giant mulit-gen space ship created by an ancient extinct race (the Ancients). Come on, who really believes that its powdery coating, which conveniently absorbs impact shocks while capturing new resources for the moon people, and its life-helping effect of strengthening our planets magnetic field are just chance? Clearly it is intelligent design.
well the wikipedia article says
"By that time, the Earth and Moon will become caught up in what are called a "spin-orbit resonance" in which the Moon will circle the Earth in about 47 days (currently 29 days) and both Moon and Earth will rotate around their axes in the same time, always facing each other with the same side. Beyond this, it is hard to tell what will happen to the Earth-Moon system"
I would think that eventually friction (there isn't much friction in space but there is some) would make the system collapse if it was left to run long enough but that is likely to be a very long way off and the sun will probablly be long dead by then (of course the death of the sun will presumablly cause complications of it's own).
note: i'm known as plugwash most places but i screwd up registering that here somehow in the past and now can't register
In addition to the other excellent comments in reply to your post here:
:-)
Recall that you can have black holes that have a very small mass, there is some research that seems to indicate we've created some microspic black holes in particle accelerators (http://news.bbc.co.uk/1/hi/sci/tech/4357613.stm)
Of course this goes to show that Einstein was wrong about the equivalence of gravity and acceleration, but that's way off topic
"The weirdest thing about a mind, is that every answer that you find, is the basis of a brand new cliche" -
Ever hear of the ancient Sumerian text speaking of a collision with Tiamat and Nibiru? There was a collision that supposedly occurred between the two planets. From this collision, the Earth and the asteroid belt was made according to the tale. It wouldn't surprise me that the moon would be made from this collision as well. Reading this article seems to reinforce this.
You can get a brief overview of the story here:
http://en.wikipedia.org/wiki/Hypothetical_planetary_object_(non-scientific)
There are many things out there that I think the masses are unaware of. The fake moon footage is definitely one of them. We have been misguided about a lot of things, including our own history. The existence of aliens, prehistoric artifacts such as bullets found in prehistoric animals, Ancient batteries, Egyptian hieroglyphs with jets and helicopters and so on.
The usual argument. A stunning amount of galaxies, each containing gazillions of stars, oodles of planets, scads of planets in the habitable zone, a whole bunch of those with moons, a fraction of which might have developed life as we can conceive of it. (Yes, those are scientific terms, you can use them.
The point is, the sheer number of stars/solar systems there have to be out there is just so damned large that we're not going to be the only planet out there with a moon like ours.
Let's face it, it's a big assed sky. Nothing is going to be 'common', that's for sure. But, statistically, there's enough of everything that it's probably not utterly unique either.
Cheers
Lost at C:>. Found at C.
[Usual disclaimers about I ain't no planetologist, etc]
This discussion of center of gravity is neat since partway down the page is an animation of the Earth and Moon orbiting their barycenter. The effect is sufficient to add a distinctive "wobble" to the Earth's orbit around the Sun: the Earth itself is about 6,000 miles closer to the Sun at the Full Moon than it is at the New Moon.
If the Earth kept the same face to the Moon at all times, the lithosphere would tend to evolve into the structure that most efficiently distributed the stress of this wobbling. But since the Earth rotates once through the barycenter every day, there are considerable dynamic forces constantly injected into the upper part of the Earth's lower mantle. The focus of these forces sweeps through that region, about 1000 miles beneath our feet, at more than 65 miles per hour. This has got to be a significant factor in geologic processes like plate tectonics, but I don't believe that geology is incorporating these forces into its models as yet.
Without the constant stirring by the tides, it is much less likely that the primordial soup of the oceans would have birthed life so quickly.
The Earth would not be what it is without the presence of the Moon. Looking at it this way, it is clear that the Earth and Moon are a binary planet: the Earth would not have its distinctive features without the presence of the Moon.
You do realise that this is middle-school physics, don't you?
I certainly wasn't taught about this directly in school at all, 15 years ago or so, and judging by your spelling, I'm from the same place as you (UK). The inverse square law people should know (though it is not, even in places like /., commonly applied knowledge), but extrapolating it to planets etc. is not immediately intuitive. Don't assume people are trolls simple because their field of expertise is not your's (I include amateur expertise in this).
The article is pretty vague about it's findings. It found 2 to 4 systems that look like a collision like the one that is thought to have created our moon took place. They don't say exactly why it must be at that time and not sooner. The ones they found are at 100 million and 400 million years after the star formed, when I think most of the planetary formation and therefore dust should have been gone (50 million years is what they say). I assume they looked at 40 stars, that gives the 5% and 10% figures. Did they take into account how long it would take for that dust to be cleared by the planets? If planet formation and the dust should be done by 50 million years, there could be many more that have already happened. They looked at a 400 million year old star that seems to have had it happen, what if they looked at another 400 million year old star that had it happen at 30 million years like our system. All the dust would have been gone by 370 million years later.
It's 5-10% of planetary systems? What's the ratio? It may seem like stars are very spread out, we usually only hear about our nearest neighbor that is less than 5 light-years away. If you pull back to 20 light-years though, you'll see 109 stars! Considering about 30% of stars have planetary systems, and 5% of those would have a collision that could produce a moon like ours, that's 1.5%. IF you take into account that our galaxy alone has between 200 and 400 billion starts, that's 3-6 billion moons like ours in our galaxy alone. If you take into account the middle numbers for star count and the percentages here, you get 6 billion. That's one moon like ours in our galaxy for nearly every man, woman and child on earth.
Ehm, no, I don't live in the UK... Continental Europe, though. That said, this was really standard stuff in my high school and I can guarantee you that the calculation I did here was on the curriculum. Actually, this together with Keplers laws was often illustrated with planets.
Sure, that's over 15 years ago. I guess, the curricula have been dumbed down by now.
This *is* basic physics and goes hand in hand with F=m*a. In this special case F=m*g, and you guessed that I actually calculated g for both Earth and The Moon! Since m2 was 1kg F=g in this case. Frankly, I can't imagine doing F=m*g without explaining where the g in that formula comes from. Hence you automatically come to F=(G*m1*m2)/r^2.
I'm not an amateur physicist, nor an amateur astronomer. I'm a mere dumb computer scientist, remembering what he had in school (and double-checking with wikipedia because frankly, I didn't know the value of G by heart anymore)
Oh, and finally, I just *asked* if he was a troll. I assumed he his innocence or he wouldn't have gotten the detailed reply that I gave.
Besides, aren't we supposed to be Nerds???
Ahhh...the great dumpster continuum. Many a free computer will be found there. -- sowth (748135)
"Virus" has a U declination, not A, so the correct Latin plural of "virus" is "virus".
Since that doesn't make sense in English, you should use viruses.
It is most definitely not "virii".
Regarding radiation and mutation rate, it seems that our (and probably all living beings') mutation rate is just about optimal for the right evolution speed in the ecological niche we're living in. Early life developed in a much harsher environment than today, with much higher UV levels (no oxygen => no ozone) for example. So, in the very early steps, life must have been able to deal with radiation, and then slacked off to keep the mutation rate at an optimum.
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My thanks to you and the many other excellent answers given by the posters. Your answer was the clearest and easiest to understand. Its been years and years since I took a course in physics, back in the early 70s, and I don't remember many details, considering all the drugs I was taking in those years.
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what are you a nerd?
Sorry about the writing. Robot fingers, you know? Cliff Steele in DOOM PATROL #23
Yes, pretty much:
http://en.wikipedia.org/wiki/Geology_of_the_Moon#Formation
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The fact that Earth's moon subtends roughly almost exactly the same angle as the sun does (as seen from Earth's surface) is merely the way it appears now. You know that the moon always points the same face toward Earth, but do you know how that comes to be? You need to understand an effect called tidal locking:
(1 of 4: description, and explanation of a familiar example):
Suppose the moon's day used to be longer than its orbital period around Earth (which it almost certainly was when the Earth-moon system formed). Since the moon is not a perfectly balanced body, there is a "heaviest part" and a "lightest part" subjected to Earth's gravity. Earth's gravity exerted a torque on the moon each lunar day, lengthening lunar days until the heaviest part of the moon always faced Earth, reaching a stable equilibrium. It's a bit like an ice cube in a drink: Earth's gravity rolls it around until either something stops its roll or the heaviest part faces Earth. Even if the moon "rolls" (spins) through unstable equilibrium, it still has rotational energy to carry it through to the stable equilibrium.
(2 of 4: generalize the example to an unfamiliar, but understandable one):
Just as the moon can be tidally locked to Earth, Earth can be tidally locked to the moon. Earth too has a "heaviest part" and a "lightest part", upon which the moon's gravitational field acts. Eventually, Earth's heaviest part will point toward the moon just as the moon's heaviest part points toward the Earth. The moon is locked because it is much less massive than the thing it [closely] orbits; the same is true with every other moon in the solar system. The same tidal locking happens to planets that orbit close to their stars.
(3 of 4: orbital energy and altitude)
But even if the moon is always over one part of Earth's surface (as Earth is always over one part of the lunar surface), that doesn't explain how the moon's apparent size would change as viewed from Earth. Remember how the moon's days got longer until the moon became tidally locked with Earth? That's how Earth's days are still growing longer, and will do so until Earth becomes tidally locked with the moon. Earth's rotational energy is being transfered to the moon's orbital energy. The moon must either destroy mass and remain at its current orbital altitude, or since it can't get rid of mass instead stay the same mass but increase its orbital altitude. The effect is that as Earth spins slower (and Earth days get longer), the moon gets farther away.
(4 of 4: Earth's oceans and ocean tides):
We already have all the basic concepts so we can basically understand what's going on, but we should look at another big effect before looking at the big picture: Earth has oceans. The combination of the moon, the spinning Earth, and Earth's oceans literally stretch Earth's mass resulting in a tidal bulge each on the side of Earth closest and farthest away from the moon, but not quite exactly toward or away from the moon. The net effect is that the moon collects Earth's rotational energy faster. Ask the internet if you want the gory details or more clarification.
As it turns out, Earth will not become tidally locked to the moon until after the moon is so far away that it subtends a smaller angle of the sky than the sun. After one last total solar eclipse, the most complete solar eclipses on Earth will be annular eclipses.
But the real coincidence is this: Over the literally billions of years of geological time, the portion during which the sun and moon subtend approximately the same solid angle of sky is small. For most of Earth's history, the moon appeared noticeably larger, and for most of Earth's future, the moon will appear noticeably smaller. We're viewing a single, small timeslice in a ~10 billion year continuum of time.
In response to the apparent coincidence of the lunar and human menstrual cycles, there are fruitful explanations from evolutionary biology. Perhaps you'd also like to consider that humans are the only creature
The stars in our local neighborhood are actually separated by distances very typical in the galaxy. The fact you've stumbled upon is that pretty much every star system is screwed in that respect. The separations between the stars are simply beyond our ability travel. We can communicate over many hundreds of light years, but only if we put up with the centuries necessary and if there's someone to talk to. The vastness of the universe provides a virtual guarantee that we have company, but also effectively isolates everyone from everyone else.
ironic captcha: serenity
What!? and ruin all those scare-stories about "radiation" from mobile phone masts and WiFi boiling your brain? :-)
In a survey of 100 programmers, 111111 thought that duck-typing was a good idea.
Storm