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Questions about Galactic Rotation

  1. Oct 22, 2011 #1
    I have two questions with regards to galactic rotations.

    Does the concept of a Galactic/Cosmic Year also apply to other galaxies apart from the Milky Way?

    Is the Galactic/Cosmic Year of other galaxies used in any analysis based on observations made of those galaxies?

  2. jcsd
  3. Oct 22, 2011 #2


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    1. All galaxies have their own 'galactic' year, but, it is a difficult thing to measure.
    2. It appears probable galaxies of similar mass and dimensions as our own have similar 'cycles'.
    3. I fail to see how such information would be useful or relevant.
  4. Oct 22, 2011 #3
    Thanks for your 2 answers Chronos,

    If you know a sources galactic year couldn't you work out the current location of that discrete source rotating around that galactic center from the images captured at the observer now?

    Wouldn't this just be a implicit part of the sources calculated Galactic year and its calculated distance away in the first place?
  5. Oct 23, 2011 #4
    As you own reference quite clearly states, the so-called galactic year is the time it takes Solar system to complete the circuit. Obviously different stars, gas clouds etc take different time to do so. Notably those on the outer edges. So... what exactly do you intend to measure in other galaxies as the yardstick for their galactic year? Some arbitrary star?
  6. Oct 26, 2011 #5
    You could probably use just one but with three you could measure their speeds of rotation at various points and map all the other rotating galactic sources according to their location with respect to the three mapped points.

    I'll put it like this Grizzled, cosmological theories that only predict the results of measurements are a bit like two legged stools, a third leg that comprises the projection of the results of the measurements back into our own physical reality would provide a stable platform to base a practical mapping/navigation/communication system on.
  7. Oct 26, 2011 #6


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    I think I see your intent and it seems straightforward and reasonable (if you know where we see a star now and we know how it fits into the rotational scheme of its galaxy, then we have a good handle on where it ACTUALLY is now, assuming we know how far away the galaxy is).

    What I do not at all get is WHY you would care. You mention having information on which to "base a practical mapping/navigation/communication system" but surely you're not planning on going to a distant galaxy are you? And as for communicating, you would, depending on the distance, not get an answer until after you're dead (or for a REALLY close galaxy, after 8 or 10 years) and even that is based on some unlikely assumptions (we have a strong enough communication method that our signal would get there, "they" would BE there, they would understand the communication, they would respond ... just to name a few).

    So again, what I'm seeing is that you are setting up a possible measurement that has zero practical use. What am I missing?
  8. Oct 26, 2011 #7
    Are you familiar with the Milky Way project running right now within the BOINC framework? If not, you may be interested to have a look.

    The purpose of the long-running project is to map the motion within our own galaxy of a jet of stars which are (presumably) the remnants of a dwarf companion galaxy which long ago collided or was absorbed by the Milky Way.

    Those stars are moving in some mighty odd orbits compared to the rest. And we are not talking about two or three... or a hundred. Even a modest dwarf galaxy and its remnants can easily count millions of original stars.

    Add to this massive perturbation of orbits within both galaxies during the collision and I submit that checking not just three or four, but even three or four hundred may be completely meaninless.
    Last edited: Oct 26, 2011
  9. Oct 26, 2011 #8
    What I'm driving at, is that the term "Galactic Year" is a bit misleading. Despite its name, it's not a property of the galaxy as such but rather of a single individual object (like Solar System) in relation to it.
  10. Oct 26, 2011 #9
    Did you mean a really close STAR per chance? Would really hate to suddenly find a whole new galaxy right at our doorstep next to Proxima at just over 4 light years away :-)
  11. Oct 28, 2011 #10
    Hi Grizzled, I had a look and it is interesting but the concept is almost opposite to what I was considering. Astronomical observation has moved from a terrestrial observer to an orbiting observer so the next logical step would be to move towards an observer in a location that is stationary relative to our own galactic rotation and finally to an observer stationary relative to our galactic rotation around the perceived universal center of rotation. BOINC could determine the best approach to realising these relatively stationary observation pathways though.

    I agree, it would be preferrable to do them all and thats what I was originally leading to. Once we have unmanned observation platforms (seen those Camera Balls on TV yet?) and a suitable communication chain we not only have something to cross check our projections from local observations we will also find out very quickly if our calculations are anyway near the observed reality.
    Last edited: Oct 28, 2011
  12. Oct 28, 2011 #11
    I'm aware of that and it made me wonder what we would see if we observed our own galaxy from another galaxy of similar makeup. The simplest example is what we call a quasar but the attached image is for 2 balanced solar systems.

    Interestingly enough, in the mid 0's a quasar pair was identified to have different repeating patterns of dimming cycles that were approximately 45-65 % consistent with the paths on the attached image. Recently reverse spiral galaxies have also been discovered.

    If we observe one galactic year of rotation in our depth of field we capture x photons. If we capture the light from 7 galactic years of rotation of the same source in our depth of field we will see 7 times x photons. If we fail to take the galactic year rotations into consideration our observed galaxy might only be 2 balanced solar systems that are actually 7 times closer and weigh 7 times less than what we calculated from the total photons collected. :wink:

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    Last edited: Oct 28, 2011
  13. Oct 28, 2011 #12
    The real practical use is that if we can get this observation/communication/navigation chain working and scaling correctly we will be able to see anything that passes by this chain under its own control (before it notices us) without spending a cent on going anywhere in person until we know where we are really going.
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