>That cycle is the draconic month, which is 27.2122 days. The tropical month is 27.3216 days, which is the length of time the moon takes to appear at the same longitude.

Wikipedia writes:

>It is customary to specify positions of celestial bodies with respect to the vernal equinox. Because of Earth's precession of the equinoxes, this point moves back slowly along the ecliptic. Therefore, it takes the Moon less time to return to an ecliptic longitude of zero than to the same point amidst the fixed stars: 27.321582 days (27 d 7 h 43 min 4.7 s).

So by this definition thats the longitude with respect to the equinoxes. I don't know how the equinoxes move with respect to geographic longitudes. I had somewhere else seen the definition that "tropical" means "with respect to the earth reference system", but at the moment I don't see quickly that the geographic longitudes should be the same as the longitudes with respect to the equinoxes.

>Try Googling "Draconic AND Chandler wobble". You won't find anything.

There might be various reasons for that is first -I don't know- but I would think that nutation theory uses coordinate systems and not those rather confusing definitions about sidereal, draconic, tropical etc. secondly you always have to take into account that your google bubble might be ill-adjusted to your purpose.