Then there are the Twelve Days of Christmas, and the counting only starts on Christmas Eve, I think, so something's slipped somewhere. Last year there was webcam inside Maeshowe that was streaming the sunsets - actually it was very cloudy for weeks - over that period. It would be easy enough to mark a windowsill with a pencil to test which was true.

To establish the solstices in ancient times would have required observation over several days both before and after in order to work out a mid-point. The number of days needed would depend on how accurately they could observe the setting point, but in the absence of lenses, line-of-sight measurements would probably require two or three days each side at the least, because the sun's annual excursion does indeed appear to "stand still".

I think it's reasonable to speculate that the point at which the exit of the solstice could be confirmed might have been a cause for great celebrations.

Does anyone know whether Yule was actually celebrated at this later time (e.g. 25th) in the pre-Christian era, rather than the Neopagan tradition of the 21st/22nd? I would have thought it likely that the early Christians would have hijacked the actual day of Yule rather than three days afterwards when everyone would have been totally sozzled from celebrating Yule. ;o)