As I understand it, our solar system travels through the milky way with the orbital plane tilted about 60 degrees so that we are sort of traveling in the direction of earth's north. My question is if our orbital plane rotates with our galactic orbit so that it maintains its orientation in relation to the center of the galaxy as I've show in this first picture.

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Or is the orientation unaffected by the galactic orbit as I've shown in this second picture.

enter image description here

  • $\begingroup$ +1 Great question! Great graphics too! $\endgroup$ – uhoh Jan 30 '19 at 14:41

The orbits in our solar system add up to a certain total angular momentum, which is a vector so points in some direction. To get that vector to point some other way requires torque, it won't happen just because the solar system is orbiting the galaxy. So the "precession" rate of the plane of our solar system is controlled by very different things than the orbital rate, so there would never be any reason for picture #1.

Picture #2 is what you get if there is no torque, so at least there's a reason for it. The kind of torque you'd need would be a force that points up from the plane on one side of the orbit and down from the plane on the other side, but a force like that would depend on distance from the Sun so it would be different for different planets. That would tend to make their orbital planes undergo nodal precession at different rates, so they would not be in the same plane. So either such torques have had no effect over the lifetime of the solar system, or else something else shepherds the planets into the same plane. But it can't be the latter, because Neptune is in the plane but Pluto isn't. So I think it must be picture #2.

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    $\begingroup$ It would be interesting to see if there's any galactic effect on the precession of Jupiter's orbital plane, since Jupiter's orbital angular momentum bears most of the solar system's angular momentum. $\endgroup$ – PM 2Ring Jan 31 '19 at 5:43
  • $\begingroup$ I think this answer is speculative about the nonexistence of certain processes. For example, it offers no explanation of why orbiting objects spin within their orbits, nor why objects spin and orbit in the same direction, nor does it consider whether systems in the same galaxy spin in the same direction and corrwlated with the galactic orbit, modulo the effect of nearby systems affecting them, as we would expect from solar system behaviour. $\endgroup$ – samerivertwice Jan 31 '19 at 7:09
  • $\begingroup$ It offers no explanation of all kinds of things that weren't asked. $\endgroup$ – Ken G Jan 31 '19 at 13:42

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