> I don't see how changing to a 13 month calendar would affect the first full moon after the spring Equinox, since the lunar cycle doesn't mesh with the solar one.
Just checked... you seem to be correct. The lunar calendar isn't aligned with this well enough. While the equinox date is fixed, the first full moon after that should bounce around by several days at least. Even allowing that it's always the Sunday after that, it still seems as if it could fluctuate by a week in either direction.
