Are there any citation or documentation showing the measured degradation of the Moon's equatorial rotation velocity (thus affecting its moon's axial rotation)?

I am looking for the drift of the Moon's axis rotational speed, presumably over 10,000 years or more.

  • $\begingroup$ I don't know of a direct source, but my guess is that the best direct measurement data for determining this would come from Lunar Laser Ranging (LLR). I would start with something like this and follow the citation trails. There is some interesting information on indirect measurements found here, but no specific citations are given. $\endgroup$
    – Dave
    Commented Oct 12, 2016 at 11:35
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    $\begingroup$ what is "axial rotation" ... ? $\endgroup$
    – Fattie
    Commented Oct 12, 2016 at 14:52
  • $\begingroup$ Presumably the motion of the celestial body that is spinning such that an axis gets formed? But I get you, so I'm clarifying the question further. $\endgroup$ Commented Oct 13, 2016 at 15:05

1 Answer 1


Since the Moon is tidally locked to the Earth, it rotates with the same orbital period as it orbits the Earth. Thus, tracking the Moon's rotational velocity is essentially the same thing as measuring the changes in its orbit - if you know one, then you know the other.

The recession of the Moon has been measured using laser ranging (see links in the answer to this question) to be about 3.8 cm / year. From that rate of change of orbital semimajor axis, you could use Kepler's third law to work out a rate of change of the Moon's orbital period, and thus of its rotational period.

  • $\begingroup$ At what distant from Earth does the Moon not become tidally-locked if the Moon keeps receding away from Earth, if that is what I am understanding from this 3.8cm/yr. $\endgroup$ Commented Sep 29, 2020 at 12:42
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    $\begingroup$ Since it is already tidally locked, it will stay locked as it recedes. It is receding because of the exchange of angular momentum with Earth, and this exchange changes the Moon’s rotation as well to keep the rotational period and orbital period the same. $\endgroup$ Commented Sep 29, 2020 at 12:55
  • $\begingroup$ Great comment and answer, Eric. That is what my son is looking for and I couldn’t answer it. Now he is asking if the Moon ever rotated before and how long ago was that (sigh). $\endgroup$ Commented Nov 16, 2021 at 14:31
  • $\begingroup$ so, there is absolutely zero perturbation nor fluctuation of this tidal lock, like ever? $\endgroup$ Commented Apr 17, 2023 at 11:16
  • $\begingroup$ So there is a drift, it is directly measured by a function of its expanding Moon orbit, and a tiny one: as lunar orbit expands, the moon axial rotation slows down, albiet a tiny, tiny amount. But by no other drift factors. $\endgroup$ Commented Mar 25 at 15:01

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