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Thread: Direction of spin in our Galaxy

  1. #1
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    Direction of spin in our Galaxy

    I was just wondering whether there is an answer to the following

    Within our solar system the majority of planetary bodies rotate in anti-clockwise directions as viewed from above.

    Presumably if the Galaxy rotates in this fashion (haven't checked but I assume that is the case)This rotation is ultimately picked up from the Galactic spin itself.

    Are there other galaxies that rotate in clockwise directions?
    and has anyone tried to count the differing directions of rotations for all the galaxies out there...?

    Thanks people
    Last edited by BlueCoyote; 2010-Jun-27 at 04:06 PM. Reason: corrections

  2. #2
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    Quote Originally Posted by BlueCoyote View Post
    Are there other galaxies that rotate in clockwise directions?
    A galaxy (or a solar system for that matter) doesn't have a top or bottom, so all galaxies spin in either clockwise or counter-clockwise direction, depending on which "up" you mean. Our galaxy included.

    The question you ask about the direction of rotation of galaxies does have a more complex answer, but it would be getting beyond your question.
    As above, so below

  3. #3
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    Quote Originally Posted by Jens View Post
    A galaxy (or a solar system for that matter) doesn't have a top or bottom, so all galaxies spin in either clockwise or counter-clockwise direction, depending on which "up" you mean. Our galaxy included.

    The question you ask about the direction of rotation of galaxies does have a more complex answer, but it would be getting beyond your question.
    If I am not mistaken, BlueCoyote was asking the direction of spin when viewed from the same North/South orientation as we generally regard the Earth, with North at the top.

  4. #4
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    It's a tough call because our Solar system is tilted some 60 degrees to the plane of the Milky Way. Any designation of "north" or "south" is purely arbitrary, as are the notions of "above" and "below". I wouldn't be surprised to learn that our galactic "north" was chosen so that it would appear to turn anticlockwise when viewed from that direction.

    The same can be said of other galaxies.

    The direction of rotation and revolution of bodies in our solar system came primarily from the rotation of the gas cloud from which it condensed. The Milky Way's rotation speed is too slow to have any noticeable effect on something that small.

    Fred
    "For shame, gentlemen, pack your evidence a little better against another time."
    -- John Dryden, "The Vindication of The Duke of Guise" 1684

    Earth's sole legacy will be a very slight increase (0.01%) of the solar metallicity.

  5. #5
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    Quote Originally Posted by BlueCoyote View Post
    Are there other galaxies that rotate in clockwise directions?
    and has anyone tried to count the differing directions of rotations for all the galaxies out there...?
    Galaxy Zoo: The large-scale spin statistics of spiral galaxies in the Sloan Digital Sky Survey

    Abstract: We re-examine the evidence for a violation of large-scale statistical isotropy in the distribution of projected spin vectors of spiral galaxies. We have a sample of ∼37 000 spiral galaxies from the Sloan Digital Sky Survey, with their line of sight spin direction confidently classified by members of the public through the online project Galaxy Zoo. After establishing and correcting for a certain level of bias in our handedness results we find the winding sense of the galaxies to be consistent with statistical isotropy. In particular, we find no significant dipole signal, and thus no evidence for overall preferred handedness of the Universe. We compare this result to those of other authors and conclude that these may also be affected and explained by a bias effect.
    Galaxy Zoo: Chiral correlation function of galaxy spins

    Abstract: Galaxy Zoo is the first study of nearby galaxies that contains reliable information about the spiral sense of rotation of galaxy arms for a sizeable number of galaxies. We measure the correlation function of spin chirality (the sense in which galaxies appear to be spinning) of face-on spiral galaxies in angular, real and projected spaces. Our results indicate a hint of positive correlation at separations less than ~0.5 Mpc at a statistical significance of 2-3 σ. This is the first experimental evidence for chiral correlation of spins. Within tidal torque theory it indicates that the inertia tensors of nearby galaxies are correlated. This is
    complementary to the studies of nearby spin axis correlations that probe the correlations of the tidal field. Theoretical interpretation is made difficult by the small distances at which the correlations are detected, implying that substructure might play a significant role, and our necessary selection of face-on spiral galaxies, rather than a general volume-limited sample.

  6. #6
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    There is no difference between "above" and "below" or between
    "clockwise" and "anti-clockwise" rotation for a planet, solar system,
    or galaxy. If you look down on one pole, you see it rotate clockwise.
    If you look down on the other pole, it rotates anti-clockwise.

    I have a guess as to why most planets in our Solar System
    rotate in the same direction as the direction of revolution about
    the Sun. When the planets were forming, nearly all matter in the
    protoplanetary disk was in circular orbits around the Sun, very
    much like the matter comprising the rings of Saturn. Those orbits
    were never perfectly circular, though, so bits of matter sometimes
    collided. When they collided, they sometimes stuck together. They
    would be most likely to stick together when the collision speed was
    low, which means their orbits were very similar. So a planetoid near
    its perihelion, moving slightly faster than average speed, would be
    most likely to collide with and stick to a planetoid near its aphelion,
    moving slightly slower than average. The day side of the planetoid
    near perihelion would be most likely to hit the night side of the
    planetoid near aphelion, because their orbits are so similar. The
    collision gives the combined planetoids a rotational acceleration in
    the same direction as their revolution about the Sun.

    The direction of rotation of a protoplanetary disk is completely
    random. It has no relation at all to the plane of the disk of the
    galaxy it is in, if the galaxy is a disk galaxy. It is determined by
    gazillions of interactions between particles in the molecular cloud
    as it collapses due to gravity. It would not be possible to predict
    the orientation of a protoplanetary disk before the molecular cloud
    began to collapse, even if you knew the speed and direction of
    motion of every particle in the cloud.

    -- Jeff, in Minneapolis

    .
    Last edited by Jeff Root; 2010-Jun-28 at 03:10 AM. Reason: added missing punctuation
    http://www.FreeMars.org/jeff/

    "I find astronomy very interesting, but I wouldn't if I thought we
    were just going to sit here and look." -- "Van Rijn"

    "The other planets? Well, they just happen to be there, but the
    point of rockets is to explore them!" -- Kai Yeves

  7. #7
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    Quote Originally Posted by Nowhere Man View Post
    I wouldn't be surprised to learn that our galactic "north" was chosen so that it would appear to turn anticlockwise when viewed from that direction.
    The conventional north galactic pole was in fact chosen just because it lies in the north celestial hemisphere. Unfortunately, this means the galaxy rotates clockwise when viewed from galactic north.

    Grant Hutchison

  8. #8
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    Thanks people - I should have realised that up and down are somewhat subjective in apparent infinite 3 dimensions

  9. #9
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    Quote Originally Posted by Me
    I wouldn't be surprised to learn that our galactic "north" was chosen so that it would appear to turn anticlockwise when viewed from that direction.
    Quote Originally Posted by grant hutchison View Post
    The conventional north galactic pole was in fact chosen just because it lies in the north celestial hemisphere. Unfortunately, this means the galaxy rotates clockwise when viewed from galactic north.


    Fred
    "For shame, gentlemen, pack your evidence a little better against another time."
    -- John Dryden, "The Vindication of The Duke of Guise" 1684

    Earth's sole legacy will be a very slight increase (0.01%) of the solar metallicity.

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