Synodic month: variations in the geologic past.
The value of 31.56 +/- 0.74 days for the synodic month in the Upper Cambrian is used together with a maximum in the expected number of days in a synodic month to argue that solar tidal dissipation is important in the dynamics of the earth-moon system and that the moment of inertia of the earth cannot have been much larger then than it is now. The tendency of the measurements to remain near 30 days may be a resonance effect.
Miller
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