If I had to guess when Jesus's actual birthday was, I'd say Groundhog Day, February 2 -- Imbolc in the old calendar of Northern Europe. Why? Well, because the shepherds were abiding in the fields, keeping watch over their flocks by night. Which probably meant it was lambing season, the traditional start of which (at least, in Northern Europe) was February 2.
But then, if they'd placed Christmas on Feb. 2, we'd miss out on the party!