Calculate the libration period in latitude (draconic month). Why is the draconic month D shorter than the stellar S

Calculate the libration period in latitude (draconic month). Why is the draconic month D shorter than the stellar S, and the anomalous one longer?

1 / D = 1 / S + 1 / R
where R is the period of revolution of the nodes of the lunar orbit. D = 27.21 days
The draconic month is shorter than the stellar one because the nodes of the lunar orbit move to the west – towards the motion of the moon, and the anomalistic month is longer than the sidereal one, because the line of apses moves to the east and the moon needs to catch up with it.

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