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I have recently learned that the polar axis of Earth moves in a complex fashion. There are both precession and nutation. I have learned that Earth's obliquity varies between 22.1 and 24.5 degrees on a 41,000-year cycle. My questions are:

  • What accounts for the change of obliquity in the range of 22.1 to 24.5 degrees besides nutation, which I assume is a relatively high-frequency process consisted of many terms (like a Fourier expansion series)?

  • Do the ecliptic or the invariant plane of the solar system rotate with respect to the distant stars, and if so, are they responsible for the variation of Earth's obliquity?

  • Lastly, how should we understand the period of 41,000 years. The wiki says something I found confusing.

This cycle is a combination of precession and the largest term in the motion of the ecliptic

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  • $\begingroup$ You can check EarthScience.SE $\endgroup$
    – Nilay Ghosh
    Commented Jul 23, 2022 at 4:27
  • $\begingroup$ Thanks for the suggestion! Should I close this question? $\endgroup$
    – hb12ah
    Commented Jul 23, 2022 at 5:02
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    $\begingroup$ This question is perfectly on-topic here. @NilayGhosh I don't think it's appropriate to make new members double-post - a thing which is definitely not wanted. $\endgroup$
    – planetmaker
    Commented Jul 23, 2022 at 5:47
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    $\begingroup$ @planetmaker I am not saying OP to double post. I am suggesting OP that we have a sister site for Earth related topics. OP may check if there is any post on this topic. $\endgroup$
    – Nilay Ghosh
    Commented Jul 23, 2022 at 6:53
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    $\begingroup$ I have some info about the stability of the ecliptic and the invariable plane here: astronomy.stackexchange.com/a/44412/16685 "the inclination of the ecliptic plane to the invariable plane of the Solar System varies by ~3°, over a very long time scale. The invariable plane itself is very stable relative to the International Celestial Reference Frame (ICRF)". $\endgroup$
    – PM 2Ring
    Commented Jul 23, 2022 at 7:07

1 Answer 1

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The axial tilt of the Earth changes its direction due to the influence of other planets, the moon, and the sun.

Nutation is due to the effects of the moon and the sun's gravity, but it is mainly due to the regression of the moon's nodal line during an 18.5-year cycle.

The precession is due to the torque exerted on the earth due to its oblateness from the moon, the sun, and other planets. Its period is about 26000 years.

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