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What if the Earth and Moon were attached to each-other?

  1. Apr 26, 2014 #1
    Hello. My name is Andrew Huerta and I am a comic creator. I am currently doing some research for a comic I'm working on and I'm having a bit of trouble grasping some of the concepts I've created.

    Basically, what would be the reality of this situation?
    10261914_10202271966692831_1275494183_n_zps4c9ade43.jpg

    Like, what would that scenario do the oceans, the view of the sky, days/nights etc...

    It would be greatly appreciated.
     
  2. jcsd
  3. Apr 26, 2014 #2

    Bandersnatch

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    Hi Andrew, welcome to PF!

    Connecting Earth and Moon mens that the Moon needs to be in a geostationary orbit, so that it always stays above the same point on the Earth's surface(ortherwise the connecting cable would start winding up around the Earth and snap). Such an orbit lies about 36000km above Earth's surface, or about 1/10th of the current lunar orbit. The plane of the orbit needs to lie in the plane of Earth's equator, else the Moon would wobble up and down as seen from the surface(again, leading to snapping of the connector thingy).

    So, for the scenario to work, you need to change the Moon's orbital inclination from 5° to 0° and bring it ten times closer.

    At such distance, it would look about 10 times larger(by diametre), spanning about 5° on the sky(about 180°). It would be 100 times brighter.

    Solar eclipses would be more frequent and longer.

    The Earth and its oceans would distort 1000 times more due to tidal forces, but after settling in the new, more oblate shape, there would be no more tides(apart from what little we get from the Sun).
     
  4. Apr 26, 2014 #3
    Thanks for the reply, BS. Some of your info is very useful, but to be clearer, in this situation, the moon does not rotate or spin at all. The structure that is holding the Moon in place is pretty much an "unbreakable" mechanical pillar. So nothing would snap or wrap around anything.

    Its pretty much like someone (Earth) spinning, holding their arm straight out while gripping a baseball (the moon). Does that make sense?

    I know this is impossible, but I just need to know what would be the realities/effects of this type of situation.
     
  5. Apr 26, 2014 #4

    Bandersnatch

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    If you are spinning and you grab a ball in your outstretched hand, then the ball necessarily is both rotating(you hold it in your hand, so it always rotates at one rotation per your own rotation, showing the same face to you - just as the Moon does now), and revolving(again, it does one revolution per your one rotation). You can't get around it - your arm is a rigid object that is firmly attached to your body.

    But perhaps you meant that you wanted the Moon to stay where it is, distance-wise, and then connect it to the Earth. You still need to match the orbital period to the daily rotation of the Earth, for the above reason.
    Once you do that, it would mean huge orbital velocity for the Moon, and so, huge tension in the connector, but since it's indesctructible...
    It also has to be magically attached to Earth(and Moon), as there's a huge force trying to pull it out. You basically need to make Earth(and Moon) indestructible as well.

    Anyway, in that scenario, you lose the tides, make eclipses more frequent, and the rest is the same.

    Oh, and in both cases the Moon is always in the same point on the sky. Some places on Earth would never see it or experience an eclipse.
     
  6. Apr 26, 2014 #5
    Great stuff, here. Ok, so for those who live on the side where the moon is, they would experience an eclipse once a day? And how long would the eclipse last? And those on the side with no moon, would still have nights but just no moon, correct?

    And no tides at all? Would there be any sea life without the tides?

    Now regarding the moon and earth pulling each other apart, wouldnt the moon just rotate with the earth peacefully as long as theres no disturbance between the 2? And would the pillar work better if it were somewhat flexible, like a spring or something, maybe even generating some kind of field or something. I dont know, just throwing ideas out there so this scenario is somewhat believable and isnt too out there.
     
  7. Apr 26, 2014 #6

    Bandersnatch

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    Re: the eclipses. Probably not daily, no. The path of the sun in the sky changes over the seasons due to the Earth axis being tilted, so the eclipses would be also seasonal. For example, in your scenario, for a person at the equator(assuming the Moon attached to the equator - which it should be else everything starts to wobble) living by the pillar, the Moon is directly overhead(zenith) at all times. The Sun passes the zenith on the equator twice a year(21 III, 23 IX). You'll get a total eclipse during those days, and partial eclipses for a few days before and after. The further North or South you live, the closer spaced the two eclipses are, with longer period of no eclipse afterwards. For a person living on one of the tropics, there's just one day(the equinox) of total eclipse. Further North/South you lose the eclipses altogether.
    East-West displacement of the observer means the Moon would be lower on the horizon in the opposite direction, and eclipses would happen as described above, but earlier/later on during the day(until you move so far E/W you can't see the Moon any more).

    The eclipses last only two minutes.

    If the pillar connecting the two bodies is to look anything similar to what you drew on your sketch(i.e., a huge bastard), then its trunk will probably eclipse the Sun much more than the Moon at its end(due to how perspective works). In other words, it'd cast a mean shadow.


    Re: the tides.
    No, no tides from the Moon. You still get the tides from the Sun(which are about 45% as strong). Remember that in reality you get the combination of the two, which sometimes reinforce and sometimes dull each other(hence e.g., the spring tide). In your scenario, there's just one kind of tides, of constant amplitude.
    I don't think we can say with any confidence how would that affect the ocean life.

    Re: the revolution.
    No, the Moon would only move peacefully in its orbit if you brought it closer to Earth(to the geostationary orbit).
    Holding a body above a single point on Earth's surface when orbiting at any other distance requires more/less orbital speed than is natural(depending if it's farther/closer than the geostationary orbit) and a constant applicaton of some external force(i.e., not just gravity) to keep the overly fast/slow body from flying away/crashing into the Earth. The material of the tether doesn't matter insofar as the basic orbital physics is concerned. It does matter in the sense that it has mass that by itself increases tension, but it's the easiest bit to handwave away with some good will on the part of the readers. Say it's made from ultra-light unobtanium or something.

    Perhaps looking into the concept of the 'space elevator' might be handy for you. It's basically an idea that uses the same physics we're talking about, so reading about it might be enlightening.
     
  8. Apr 26, 2014 #7
    Hi Andrew!

    If the Moon were in geostationary orbit, then the tether ought to be about [edit: 4.5] times the diameter of the Earth, so your sketch shows the moon too close and too large.

    Are you intending the Earth to have a normal length day? The geostationary orbit that Bandersnatch talks about gets further away if the Earth is rotating more slowly. You can keep the moon in it's current position if you slow the Earth's rotation to match the moon. Then a day would be 27.32 normal days long, and you'd have a vastly longer tether that might contain more mass than the earth itself. You would also need to eliminate the Earth's axial tilt - so no more seasons. This would give you the same reduced and more predictable tides that Bander describes, but they would be based on the much longer day.

    Back to Bandersnatch's model: I'm wondering how gravity would behave on the tether. If it is as thick and heavy as your drawing suggests, one might be able to walk from the Earth to the Moon. The atmosphere of the Earth would also drift up the cable and mingle with that of the moon. (This could be bad, as it would also allow the atmosphere to escape into space.) But for a while at least, the moon might have a breathable atmosphere.
     
    Last edited: Apr 26, 2014
  9. May 12, 2014 #8
    The angular momentum of the earth's spin would be spread out over the earth & moon. That means a day would get a lot longer- someone else can work out the numbers. Too long of a day would roast the day side and freeze the night side- might even boil the oceans on the day side. Try plugging that into a climate-change model! Anybody's guess if life could survive.
     
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