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Moon Space Science

Earth's Moon is a Rarity 202

Posted by Zonk from the lucky-to-have-you-luna-old-sod dept.
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.'"
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Earth's Moon is a Rarity More

Earth's Moon is a Rarity

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  • What's also rarer. (Score:5, Funny)

    by Anonymous Coward on Thursday November 22, 2007 @06:43PM (#21449653)
    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.

  • Asimov? (Score:5, Interesting)

    by TheRaven64 ( 641858 ) on Thursday November 22, 2007 @06:44PM (#21449669) Journal
    In Asimov's Robots/Empire/Foundation series the Earth was unique in having a large moon. The strong tidal forces caused a greater degree of radiation on the surface than most planets, giving the Earth a much faster mutation rate, causing humans to be the first species to evolve intelligence.

    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.

    • Re: (Score:3, Insightful)

      by Brian Gordon ( 987471 )
      This is exactly what I thought of- but I doubt a distinctive moon would be much help for future earth-hunters, since 5-10% of the entire galaxy is, um, quite a lot.

    • Not convinced (Score:5, Interesting)

      by Moraelin ( 679338 ) on Thursday November 22, 2007 @07:59PM (#21450079) Journal
      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

      • Re: (Score:3, Informative)

        by mandopoet ( 99292 )

        There's a book mostly intended as a resource for sf writers, What if the Moon didn't Exist? [amazon.com] , which details many of the poor consequences for creatures like us given the absence of a large moon for earth. Its been years, but I remember two of the big ones.

        First, without tidal interaction with a large moon, the earth would spin a great deal faster on its axis, resulting in much stronger and consistent winds. It would be hard for anything to be more than a few inches tall except in the windshadow of tall

        • First, without tidal interaction with a large moon, the earth would spin a great deal faster on its axis, resulting in much stronger and consistent winds. It would be hard for anything to be more than a few inches tall except in the windshadow of tall mountains, which themselves would erode much faster.

          Uh, look at Venus please. It's the same size as Earth, it formed in a slightly faster spinning band of the accretion disk, yet it spins a heck of a lot slower. In fact, if you look at the 4 rocky planets' tim

        • The Earth would still have substantial tides without a moon. If I recall correctly, the solar component of tides is about 25% of the lunar component. But that'd still be significant. It's the reason that some high tides are higher than others.

          And I might as well throw my other comments in here as well:

          1. The slowing of the Earth's rotation due to tidal friction is well established. It's good physics and there is even some evidence for slowing of about 2 hours in the past 370 million years based

      • Re: (Score:3, Insightful)

        by Pr0xY ( 526811 )
        All in all I agree with your comments, they tend to be well thought out. However, you seemed to glance over the fact that mutations relevant to evolution occur during conception, not after birth.

        Sure your body has lots of defenses against mutation, because like you said, if the cells just do what they want _after_ you are born, then, as you said, it falls apart very quickly.

        But it is a different story when the body is still being "designed" when the DNA that makes up the new life has mutations, THAT's when
        • Well, just for the sake of quoting my own posts:

          So what would happen if less cosmic radiation caused mutations on Earth? Well,

          A) buggerall, that's what. That's a tiny part of the mutations that have any role. Sure, UV might give you a skin cancer, but it won't mutate your eggs/sperm/embryo, depending on what gender you are.

          So I'd say I've at least brushed with that aspect :)

          Maybe it wasn't that explicit and clear, but I think my posts are huge as they are. Going into even more details, well, probably even l

    • Asimov did say it first, and not just in fiction (Score:5, Interesting)

      by KWTm ( 808824 ) on Thursday November 22, 2007 @08:01PM (#21450087) Journal
      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 [amazon.com], 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?

      • Re:Asimov did say it first, and not just in fictio (Score:5, Informative)

        by MichaelSmith ( 789609 ) on Thursday November 22, 2007 @08:35PM (#21450249) Homepage Journal

        So, what's this about how the Earth's moon is unique? Is this something new?

        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.

        • Re: (Score:2, Insightful)

          by RealGrouchy ( 943109 )
          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>

          • Re:Asimov did say it first, and not just in fictio (Score:4, Informative)

            by IvyKing ( 732111 ) on Thursday November 22, 2007 @11:47PM (#21451213)
            W-e-l-l, the distance from the earth to the moon is about 60 earth radii and the moon is about 1/80th of the earth's mass, so that puts the center of gravity about 1/4 of the way to the center of the earth. Whether one quarter of the distance to the center is "well beneath" is open to interpertation.


            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.

    • Re: (Score:2)

      by gatkinso ( 15975 )
      The End of Eternity was a dumb book. So in th 130,000th century man FINALLY travels to other star systems to find them colonized by aliens. Man then return to eath the wither away.

      Or...

      Man simply travels back 100,000 years (or how ever long they need to go back) and colonize BEFORE the aliens do - after all they had had time travel for thousands of years.
      • Maybe those aliens had time-travel to and could prevent monkeying around on their planets' history directly.

        Or, you know, time travel storylines are basically impossible to get right. The themes shone through nevertheless.
      • 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 tra

    • Re: (Score:3, Interesting)

      by rbanffy ( 584143 )
      "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."

      It's been a while since I read those, but, IIRC, it was Asimov himself who wrote that line and, in the book, it was told as a legend that has been told for countless generations.

      As such, it could have some resemblance to reality, bu also include many elements of fiction.

      And
      • In Foundation's Edge, Asimov made a reference to the Eternals, who ensured that Earth was the only planet in the galaxy with intelligent life. In The End of Eternity, it was clear that the Eternals were humans and that they (eventually) ensured this by making sure that humans (who evolved first anyway, for reasons explained in Robots and Empire) discovered nuclear energy a few centuries early and developed space travel before they could get side tracked by time travel. In this book, there were also numero

    • Re: (Score:2)

      by rtb61 ( 674572 )
      Actually planets with in compact star clusters are for more likely to have a higher evolution rates as the interacting ort clouds will result in more common impact driven mass extinction events leaving many vacant niches with in the environment for mutating life to fill. Interestingly enough the major survival trait in those locations would be the ability to forecast and prevent future impact events either that or the ability to permanently leave a planets surface.

      High radiation would just leave life evo

  • I thought this was commonly known? (Score:5, Informative)

    by naelp ( 1112949 ) on Thursday November 22, 2007 @06:47PM (#21449693)
    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? [wikipedia.org]

    • Re: (Score:2, Interesting)

      by MLCT ( 1148749 )
      That (at least the text on wikipedia) is in the context of our own solar system (and the rare earth hypothesis generally is not a very strongly scientific area, it is a bit too "we haven't yet seen anything like us so we *must* be special")

      The evidence brought forth by this science is looking at the current (relative) stars that are forming and finding what percentage are likely to have moon formation occurring at around the time that our moon was formed. The figure is surprisingly low - but like most c
    • 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.
      • 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 th

        • Re:Why this might matter (Score:5, Interesting)

          by yotto ( 590067 ) on Thursday November 22, 2007 @09:30PM (#21450567) Homepage
          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.

          Uranus doesn't point one pole at the sun year round. It points one pole at the same area in its "sky" year round.

          Imagine if our north star wasn't Polaris, but instead, say, Aldebaran (Which is in Taurus). When the sun is in Taurus, the North pole would point at the sun. 6 months later, the South pole would point at the sun. In "spring" and "autumn" the sun would be over the equator.

          So north and south of the equator, you'd have 6 months of darkness (read: COLD) and 6 months of light (read: HOT). On the equator, the sun would, over the course of a year, go from the southern horizon to the northern horizon, and back. When it was significantly above the horizon, it would rise and set in much the way it does now.

          No idea if that'd be habitable or not, but it would assuredly not be "fairly stable"

          • Re: (Score:2, Funny)

            by Tablizer ( 95088 )
            You are correct. My mistake. Unlike you, I don't visit Uranus often enough :-)

            Until life developed migratory patterns (or perfected hibernation), it would freeze for 6 months and then be too hot for another 6. Near the equator it would be less extreme, but still have wide swings.
                 
    • That's a scientific hypothesis -- this sounds more conclusive from lack observations of dust around nearby stars.

      It surprised me they can detect and not detect dust around nearby stars, but still have a hard time doing the same with Earth-sized objects, but maybe the "dimming" of their light is noticeable enough, or should be according to the theories, and the observations don't follow...
    • The key word is hypothesis. A hypothesis is a statement without any supporting scientific evidence. Scientist no very little about the nature of life to give Rare Earth Hypothesis any more credence than a galaxy teeming with life. This was an actual experiment done that can be scrutinize later. Proving that the moon is rare would essentially give the first experimental support. But it would still be far from proving it.

  • Oblig: The "Moon" - A ridiculous liberal myth (Score:5, Funny)

    by Anonymous Coward on Thursday November 22, 2007 @06:58PM (#21449765)
    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!)

    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 .. 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.

    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.

    • Re: (Score:3, Informative)

      by vux984 ( 928602 )
      "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."

      Yeah, I know you were joking, but 1950? I've got a copy of Jules Verne's 1865 "From Earth to the Moon", and 1870's "Around the Moon" both published prior to 1950.

      I'm sure there are people with bibles published a couple hundred ago, all with a few dozen mentions of the moon

      • Re: (Score:2, Funny)

        by Anonymous Coward
        You do know that the printing press was actually invented in 1948 as a direct result of Nazi research in World War II, right? These books that supposedly predate 1948 are all elaborate fabrications.

      • Good nutter theories are supposed to be a little harder to disprove.

        Oh another "good" theory snob. You and all those "good" scientists with their "good" theories and their "grants" and ect. ect. But just mention the popcorn theory of galactic gravity and all of a sudden your a "bad" scientist and you don't get invited to the vip area of the astrophysics seminar anymore.

      • Re: (Score:2)

        by 4D6963 ( 933028 )

        Duh. I was going to try and make a funny reply, but your comment just killed my buzz. Obviousness overload combined with a subtleness deficiency I guess..

    • I don't get it. Where's the funny?

  • Huge moon (Score:5, Insightful)

    by eebra82 ( 907996 ) on Thursday November 22, 2007 @07:03PM (#21449797) Homepage
    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.

    • Re: (Score:2)

      by dpilot ( 134227 )
      You might be right. You probably are right.

      But we don't really know that much about planetary formation. Last I read, none of our planetary formation models generated our own solar system, though there has no doubt been progress since I last read. Still, until we can study some sample of solar systems (note the plural) in detail, we really won't have a very good handle on what's going on. At the moment about all we can detect are bodies too big to really be of interest, unless we're really looking for E
    • I know Wikipedia isn't the most reliable source to quote, but some people actually seem to think the Earth / Moon is a "double planet" arrangement:

      The Earth-Moon system is sometimes considered to be a double planet rather than a planet-moon system. This is due to the exceptionally large size of the Moon relative to its host planet; the Moon is a quarter the diameter of Earth and 1/81 its mass. However, this definition is criticised by some, since the common centre of mass of the system (the barycentre) is l

  • Scientists talking about the moon?!? (Score:5, Funny)

    by Cryacin ( 657549 ) on Thursday November 22, 2007 @07:08PM (#21449825)
    Bunch of lunatics.

  • Rare defined as 5 - 10 percent ? (Score:5, Insightful)

    by dbcad7 ( 771464 ) on Thursday November 22, 2007 @07:36PM (#21449973)
    Theres 20 people in the room..1 to 2 of them have a birthmark on their left cheek... how RARE.
    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.

    • Re: (Score:2)

      by RuBLed ( 995686 )
      maybe its a 5-10% moon drop rate... now that's rare...

    • Re: (Score:2)

      by 4D6963 ( 933028 )

      Well when you think that it's 5-10% for only one such moon in whole planetary systems, that makes it quite rare indeed.

  • 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.

    • Re: (Score:3, Informative)

      by DJ Rubbie ( 621940 )
      Not according to official definitions for binary systems, because the barycenter of the Earth-Moon system is less than the radius of the major body, in this case Earth. On the other hand, Pluto-Charon system has a barycenter above the surface of Pluto, hence it is a binary planet (well, dwarf planet) system.

      http://en.wikipedia.org/wiki/Double_planet [wikipedia.org]
      • Pluto is a dingleberry dipshit of a Kuiper Belt Object with delusions of planethood.
      • Yeah. That's why our system is called the Solar-Jovian System; the barycenter of the Sun+Jupiter is above the Sun's surface.
    • The Earth and Moon arguably form a binary planetary system.Only if the barycenter lies above the surface of both objects. Otherwise, one is the planet and the other is the moon.

  • Earth's Moon is a Rarity? (Score:4, Funny)

    by Peter Cooper ( 660482 ) on Thursday November 22, 2007 @07:59PM (#21450081) Homepage Journal
    Of course it's a rarity, there's only one moon belonging to the Earth.
  • Actually, it looks like the Pluto/Charon system has similar origins: Link [spaceflightnow.com]

    So potentially 2/9 so far...

  • 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?

    • Re:Eventually (Score:5, Informative)

      by CrazyTrashCanHead ( 621556 ) on Thursday November 22, 2007 @08:46PM (#21450315)
      While it's true that the moon is currently receding, it will eventually stop and begin approaching the Earth, then pass the Roche Limit, break up, and generally cause everyone to have a bad day. However, the universe might not last long enough for that to happen. As for the proto-earth/moon impactor, it was absorbed into the system, with the lighter materials of both it and proto-earth forming the moon, while the two cores sank to the bottom of what became Earth.

    • Re: (Score:2)

      by 4D6963 ( 933028 )

      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?

      Err, obviously part of it merged with the Earth and what got ejected made up the Moon along with stuff originally belonging to the Earth?

  • A rarity also in terms of a lottery win (Score:3, Interesting)

    by caywen ( 942955 ) on Thursday November 22, 2007 @09:14PM (#21450473)
    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.

  • Giant Space Mouse (Score:3, Funny)

    by vjmurphy ( 190266 ) on Thursday November 22, 2007 @09:18PM (#21450503) Homepage
    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.

    • Re: (Score:2)

      by Nimey ( 114278 )
      If you have a Relativistic Space Mouse going through your solar system, you don't want it pooping toward any of your planets.

  • Moon's diameter as viewed from Earth (Score:5, Interesting)

    by jiawen ( 693693 ) on Thursday November 22, 2007 @11:19PM (#21451087) Homepage

    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.

    • Re:Moon's diameter as viewed from Earth (Score:5, Interesting)

      by Anonymous Coward on Friday November 23, 2007 @12:19AM (#21451351)
      i also find that notably coincidental - it's more or less a tight fit.

      and please forgive my woo here,
      but i also find it weird that the human menstrual cycle so closely matches the lunar,
      while pretty much every other mammal's doesn't.

      i'm as science-minded as they come,
      but these are each eyebrow-raisingly coincidental.
      • There alot of planetary and sun cycles,which were correlated to seemingly unrelated things like epidemics and stock market behavior.I don't think they are exact predictions,just a number that matches. "correlation is not causation".
      • 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?

    • Re: (Score:2, Funny)

      by Kutsal ( 514445 )
      Because that's not a moon. And when we send a spacecraft up there to map its interior, we'll find out that our moon is not really a moon but a 50000-year old battleship, an Utu-class planetoid named Dahak, stuck here because of a failed mutiny attempt.. :)

  • 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 spacesh
  • I love the theories swirling around this word.

    Carry on.

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