If the Christian beliefs do indeed bring about a p’gam, as it were, into our Torah, why does it go by the solar calendar? I don’t know if anything besides for V’sain Tal Umatar goes by the solar calendar.
Even if it goes by the solar calendar because the people who initiated it used that calendar, what about the ten days which the Gregorian calendar skipped in 1582? Shouldn’t Nittel Nacht be before January 4th then?