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Planes of rotation

  1. Mar 12, 2014 #1


    Staff: Mentor

    I'm not sure if this belongs in Astronomy or Astrophysics.

    Todays APOD featured the rotation of the sun about its own axis. It seems to me that the axis of rotation of the sun should be aligned with the axis of rotation of the plane of rotation of the planets, i.e. the ecliptic, or more accurately the invariable plane of the solar system.

    Wikipedia says:

    Most of the bodies of the Solar System orbit the Sun in nearly the same plane. This is likely due to the way in which the Solar System formed from a protoplanetary disk. Probably the closest current representation of the disk is known as the invariable plane of the Solar System. The Earth's orbit, and hence, the ecliptic, is inclined a little more than 1° to the invariable plane, and the other major planets are also within about 6° of it. ​

    What about the inclination of this invariable plane with the plane of rotation of the sun about its own axis?

    Is there a mechanism to make the deviation in solar/planet axis inclination converge or diverge with time?

    What about the inclination of the solar system's plane with respect to the galactic plane?

    What about the inclination of the Milky Way's plane compared to those of nearby galaxies?

    Are there clusters of galaxies that seem to share co-aligned axes of rotation? If yes, that suggests that they may have evolved from the same protoplasmic disc.
  2. jcsd
  3. Mar 12, 2014 #2


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    What about the inclination of earth's axis of rotation w.r.t. the plane of the ecliptic (23 degrees)? Or that of Uranus (97.8 degrees)?
  4. Mar 12, 2014 #3

    D H

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    It's close, 7.25°, but why would you think that? The Sun has lost a lot of its original angular momentum due to radiation, solar wind, and larger scale events such as coronal mass ejections. Those would have to be uniform to make the alignment remain constant.

    Keep in mind that the rotations of the planets are not nearly as strongly correlated with the invariable plane as are the orbits of the planets.

    As mentioned, its 7.25°.

    Mercury is essentially tidally locked. Whatever rotation it had when it was formed is long lost. Venus, too, has lost whatever rotation it originally had. Like Mercury, Venus appears to be in a final configuration. Further out, those gravitational torques become small. The Moon's torque on the Earth is considerably more than that by the Sun. Beyond the Earth, solar torque is just too small.

    About 63°. Better, about 117°. The planets rotate somewhat retrograde with respect to the galactic rotation. There is no correlation. This is borne out by observations of other planetary systems. It's essentially random.

    Again, it's random.
    Flin, P. The Search for Galaxy Orientation in the Local Group in Proceedings of the 192nd symposium of the International Astronomical Union, 1999.
  5. Mar 13, 2014 #4
    Hmm, that could be. How about precession of the Sun's axis due to gravity of the galaxy?
  6. Mar 14, 2014 #5

    D H

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    Galactic tidal gravity may well have an influence on the Oort cloud. At a distance of a light year from the Sun, those small galactic tidal forces become large enough to be a perturbative effect on the weak gravitational acceleration toward the Sun. At a scale of 50 AU (less than a thousandth of a light year), those galactic tides become negligibly small. At a scale of a solar radius, they are essentially non-existent.
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