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Does the Earth's orbit around the sun exhibit nodal precession, as does the moon's around the Earth? If it does, that must mean that the ecliptic is in a periodic wobble with respect to the celestial sphere?

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  • $\begingroup$ The ecliptic is in periodic wobble wrt the celestial sphere, but that's because of nutation, not precession. Precession (nodal precession) changes where the Sun is during the equinoxes and solstices. The Spring Equinox, for example, has moved from Aries (it's still called "the first point of Aries") to near the Taurus-Gemini border. $\endgroup$ – barrycarter Sep 3 '17 at 12:56
  • $\begingroup$ Done, though I don't think my comment was answer-worthy and definitely not bounty-worthy, but, hey, since you posted the bounty... $\endgroup$ – barrycarter Sep 5 '17 at 0:59
  • $\begingroup$ @Barrycarter, the first point of Aries is now in Pisces. $\endgroup$ – Dr Chuck Oct 5 '17 at 8:13
  • $\begingroup$ @DrChuck How embarrassing. You are correct, of course, and it is moving towards Aquarius ("the age of Aquarius"). I meant the summer solstice of course. I will feel bad about myself for the next 6 hours as penance. $\endgroup$ – barrycarter Oct 5 '17 at 13:48
  • $\begingroup$ @barrycarter Hope you are feeling better now. $\endgroup$ – Dr Chuck Oct 5 '17 at 20:06
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The ecliptic is in periodic wobble wrt the celestial sphere, but that's because of nutation, not precession. Precession (nodal precession) changes where the Sun is during the equinoxes and solstices. The Spring Equinox, for example, has moved from Aries (it's still called "the first point of Aries") to near the Pisces-Aquarius border

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  • $\begingroup$ I am aware of the nutation in Earth's axial tilt...same thing you mention? Let me ask differently: the lunar orbit around Earth exhibits westward precession (the nodes rotate around the ecliptic plane.) Kind of like a coin spinning on a table. Does the Earth's orbit of the Sun do basically the same thing, two other motions being eccentricity chg and apsidal precession? $\endgroup$ – charlie K3 Sep 5 '17 at 23:28
  • $\begingroup$ also I have read a figure of 70,000 yrs as the periodic cycle of the "nodal precession" I'm trying to understand, if that helps. $\endgroup$ – charlie K3 Sep 5 '17 at 23:32
  • $\begingroup$ @kathyslover OK, I think you're talking about "apsidal precession" which is described at en.wikipedia.org/wiki/Apsidal_precession -- however, the 70,000 year number appears only on en.wikipedia.org/wiki/Milankovitch_cycles#Orbital_inclination $\endgroup$ – barrycarter Sep 6 '17 at 22:20
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    $\begingroup$ Can you help me understand better; are you answering yes or no to the first part of the question "Does the Earth's orbit around the sun exhibit nodal precession?" Also it sure looks like you are talking about nodal precession of the Earth's axis. The question is about the nodal precession of the Earth's orbit. Can you first clearly address issues of the Earth's orbit, and put discussion of the Earth's axis perhaps in a separate paragraph so that they don't get mixed up? Just saying nodal precession without specifying of what makes this answer difficult to understand. $\endgroup$ – uhoh Sep 11 '17 at 16:27
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    $\begingroup$ @uhoh I agree: my answer is wrong for the reasons you state. It's only in the comments that I get it right. I'll try to fix my answer, but feel free to edit if you'd like. I'm also not sure I fully understand apsidal precession (Stellarium doesn't appear to model it), so my only real answer is the link I give in the comments. $\endgroup$ – barrycarter Sep 11 '17 at 16:30

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