If the solstice is taken as the moment of the sun's greatest elevation in the southern sky, and the full moon as the moment of the moon's greatest elongation, then the two moments probably coincide rarely, if ever.

On the other hand, if the solstice is assigned always formally to December 22 and the full moon always to the 15th day of the lunar month by the Gregorian Easter cycle, then the two coincide normally every nineteen years, with occasional exceptions due to adjustements occuring in some years divisible by 100.

If the solstice is assigned formally to the Universal Time calendar day on which the solstitial moment occurs, and the full moon is assigned formally to the Universal Time calendar day on which the moment of greatest elongation occurs, then the "every thirty years or so" estimate may be right.

The Roman consular year began on January 1st, and the Kalends-of-January- or Circumcision-style was sometimes used in the middle ages, as well as the Christmas-style. I suspect it is sometimes not easy to tell which is being used. Even when the English civil calendar (which was Julian until the 18th century) switched to a March 25 style, almanac-makers continued to reckon the year from January 1st. So to imply that the Julian calendar invariably used Christmas-style is misleading.

Lunar perigee at full moon is nice, though.

T.