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I was actually surprised that if all the planets were lined up, the center of mass would be outside the surface of the Sun. I had always assumed that the Sun wa

I was actually surprised that if all the planets were lined up, the center of mass would be outside the surface of the Sun. I had always assumed that the Sun was so massive that the center of mass was almost fixed and certainly always within its surface. I guess I hadn't factored in the fact that the planets are so far away and the Sun so small that their masses could have such large measurable outcomes on the center of mass of the system.

thret 7y ago
Well, 'the Sun so small' is a phrase I have never seen before.
- toyg 7y ago
  There is always something bigger, isn’t it...
  - TeMPOraL 7y ago
    https://en.wikipedia.org/wiki/List_of_largest_stars#/media/File:Star-sizes.jpg https://en.wikipedia.org/wiki/List_of_largest_stars#/media/F...
- maxnoe 7y ago
  No? Never saw videos like this one? https://youtu.be/i93Z7zljQ7I https://youtu.be/i93Z7zljQ7I
LifeLiverTransp 7y ago
I wonder wether this center of mass moving around in the sun, is producing - time delayed of course- the "sun-weather" aka, the dark spots and solarflares.. Something else: Technical the orbit, is a spiral of the whole system around the center of mass, slightly deteriorated by remainders of old interactions. Which got me thinking, if you run a astronomical simulation backwards- can you computate old interactions and "gone" missing bodys from that? Use celestial motion as a sort of archive-trail to go back along?
- ses1984 7y ago
  I think our ability to look backwards is limited by the precision of our instruments and the precision of floating point computation. Any error in our measurements would be magnified as we look backwards to the point that the simulation would at some point significantly diverge from reality, I wonder how many years back you can look before that happens? Also floating point error would compound on top of that.
  - fjsolwmv 7y ago
    Floating point error is far far smaller than measurement error and missing data.
  - chrisweekly 7y ago
    I'm no physicist, but isn't the 3-body problem relevant here too?
    - mason55 7y ago
      Only in the sense that you couldn’t directly compute the locations at arbitrary points in time given current positions and velocities. The three body problem doesn’t stop you from running a simulation and getting the correct answer.
      - dwaltrip 7y ago
        I think the point was that n-body systems with n>2 are chaotic, such that very small differences in starting position lead to massive differences as time unfolds. Wouldn't this make it very difficult to do the highly precise detective work needed to find alleged former solar system bodies? Or are simulations accurate enough these days?
        alanbernstein 7y ago
        Not an expert, but I think n>2 means that chaotic behavior is possible, but not inevitable. Consider an isolated sun-earth-moon system, that doesn't appear to be chaotic. Simulating a "3-earth" system would, AFAIK, usually be chaotic. I'd be happy to be corrected, of course.
jgtrosh 7y ago
Well it is outside the surface right now, no need to imagine all planets being perfectly lined up.

thret 7y ago

Well, 'the Sun so small' is a phrase I have never seen before.

toyg 7y ago
There is always something bigger, isn’t it...
- TeMPOraL 7y ago
  https://en.wikipedia.org/wiki/List_of_largest_stars#/media/File:Star-sizes.jpg https://en.wikipedia.org/wiki/List_of_largest_stars#/media/F...
maxnoe 7y ago
No? Never saw videos like this one? https://youtu.be/i93Z7zljQ7I https://youtu.be/i93Z7zljQ7I

LifeLiverTransp 7y ago

I wonder wether this center of mass moving around in the sun, is producing - time delayed of course- the "sun-weather" aka, the dark spots and solarflares.. Something else: Technical the orbit, is a spiral of the whole system around the center of mass, slightly deteriorated by remainders of old interactions. Which got me thinking, if you run a astronomical simulation backwards- can you computate old interactions and "gone" missing bodys from that? Use celestial motion as a sort of archive-trail to go back along?

ses1984 7y ago
I think our ability to look backwards is limited by the precision of our instruments and the precision of floating point computation. Any error in our measurements would be magnified as we look backwards to the point that the simulation would at some point significantly diverge from reality, I wonder how many years back you can look before that happens? Also floating point error would compound on top of that.
- fjsolwmv 7y ago
  Floating point error is far far smaller than measurement error and missing data.
- chrisweekly 7y ago
  I'm no physicist, but isn't the 3-body problem relevant here too?
  - mason55 7y ago
    Only in the sense that you couldn’t directly compute the locations at arbitrary points in time given current positions and velocities. The three body problem doesn’t stop you from running a simulation and getting the correct answer.
    - dwaltrip 7y ago
      I think the point was that n-body systems with n>2 are chaotic, such that very small differences in starting position lead to massive differences as time unfolds. Wouldn't this make it very difficult to do the highly precise detective work needed to find alleged former solar system bodies? Or are simulations accurate enough these days?
      - alanbernstein 7y ago
        Not an expert, but I think n>2 means that chaotic behavior is possible, but not inevitable. Consider an isolated sun-earth-moon system, that doesn't appear to be chaotic. Simulating a "3-earth" system would, AFAIK, usually be chaotic. I'd be happy to be corrected, of course.

jgtrosh 7y ago

Well it is outside the surface right now, no need to imagine all planets being perfectly lined up.