How fast is the Moon receding?

From: (Tim Thompson)
Date: 23 Jan 1996 22:48:17 GMT
Organization: Jet Propulsion Laboratory, Earth and Space Science Division

In article <4e1c1k$>, (Brett J. Vickers) writes: > There's a short blurb on this in the old-earth FAQ > at :

Editor's Note The FAQ mentioned above has since been replaced with a Moon Recession FAQ and an Age of the Earth FAQ.
>  17. The moon has been observed to be moving away from the earth at
>  about 4 centimeters per year.  At this rate the earth-moon pair would 
>  have to be less than 1 billion years in age. (8)
> Another spurious linear extrapolation. This is due to angular momentum
> transfer between the earth's rotation and the moon's revolution due to
> tides. (The tidal bulge rotates with the earth, because of frictional
> drag, and pulls the moon along with it, so the moon is being
> accelerated into a higher orbit.)  This effect is definitely
> non-linear over the timespan claimed.
This tidal argument for a young Earth-Moon system was advanced by the infamous Thomas G. Barnes of ICR fame, the same one who tried to use the Earth's magnetic field to the same effect. Barnes made the claim in a letter to the editor of the Quarterly Journal of the Creation Research Society, in December 1984. In it he referenced a paper by Louis Slichter (Slichter, 1963) where the problem seems first to have become really evident in celestial mechanics. However, this is just another example of Barnes' "selective" style of "research", since the paper by Kirk Hansen (Hansen, 1982) was already 2 years old when Barnes made his claim.

Slichter had noted in his paper that the Moon seemed to be moving away from the Earth uncomfortably fast, and that running the system backwards at the constant rate put the moon too close in the too recent past. However, Slichter was the first to try to tackle this rather difficult problem in any detail, but even his approach required many simplifying assumptions.

Once the problem was made known by his work, others went to work on the problem. In the usual method, they proceeded to pare away the assumptions, and attack the problem with more vigorous mathematical methods. The result was the discovery that the tidal response function of the oceans was really far stronger, and far more complex than had been assumed. Slichter could not handle the oceans properly, the mathematical methods were in fact developed in response to his work. Also, since Slichter published in 1963, he did not give much thought to the then relatively new idea of continental drift, or plate tectonics. But later researchers discovered that as the continents move around in the oceans, on geological time scales, the tidal response function of the oceans changed on similar time scales, in response. The ocean response function has an extremely complex spectrum of resonance states depending on the distribution of continental masses, and the current distribution has the oceans in resonance. The result is that the current recession rate of the Moon from the Earth is anomalously high and cannot be "uniformitarianly" run backwards.

As you can see by checking the references, this is an example of one of the standard weaknesses of "creation science". In this case, the young Earth types jumped on Slichter's paper like it was a gold mine, a physicist had shown that the Moon was moving too fast! Their reaction is typical of their tendency to treat science as if it were static and featureless, as if the answer of today is the answer for all time. They continue to do as Barnes did. Barnes cited Slichter's paper 20 years after it was published, yet completely ignored all of the work that had gone into solving Slichter's dilemma, and was all in the literature before Barnes even brought it up.


Bursa, M. "The Earth-Moon Tidal Force Function" The Moon and Planets 28: 49-53 (1983) [This Journal is now named "The Earth, Moon and Planets"] [Bursa presents a detailed mathematical derivation of the tidal function, but does not appear to address the internal dissipation of the oceans at all. However, if you think this is a "simple" problem, this paper will show you otherwise]

Finch, D.G. "The Evolution of the Earth-Moon System" The Moon and the Planets 26: 109-114 (1982) [This Journal is now named "The Earth, Moon and Planets"] [Finch's approach was different - he devised another form for the tidal coupling. However, his result also produced an acceptable Earth-Moon history]

Hansen, Kirk S. "Secular Effect of Oceanic Tidal Dissipation on the Moon's Orbit and the Earth's Rotation" Reviews of Geophysics and Space Physics 20(3): 457-480 (August 1982)

Lambeck, Kurt "The Earth's Variable Rotation: Geophysical Causes and Consequences" Cambridge University Press 1980 ISBN 0-521-22769-0 QB 633.L35 See chapter 6, "Tides" and chapter 10, "Tidal Dissipation"

Slichter, Louis B. "Secular Effects of Tidal Friction on Earth's Rotation" Journal of Geophysical Research 68(14): 4281-4288 (July 15, 1963)

Speaking only for myself ...
Timothy J. Thompson,    

California Institute of Technology, Jet Propulsion Laboratory ...
Earth & Space Sciences Division, Terrestrial Science Element ...
ASTER Project Atmospheric Corrections Science Team ...
Secretary, Mount Wilson Observatory Association ...
Board of Directors, Los Angeles Astronomical Society.

Last modified: 11 June 2000

Up to the Coral page.

Back to the Creation/Evolution page.

Email a comment.

Search this web site