Why is Christmas December 25?
Well, it's a date that is exactly one week before New Year's Day. But it was set then for several reasons.
In Rome, at the time the calendar was finally regularized by Julius Caesar (46 BC), the winter solstice fell on December 25 in most years (in Rome nowadays, it falls on December 22 in most years). The slippage from Dec. 22 to Dec. 25 happened between 46 BC and 325 AD, the date of the first Council of Nicaea, which adopted the dates of Easter according to the date of the Spring equinox in that year. The current (Gregorian) calendar was regularized to 325 AD, and because the date of Easter had been set by that council, that year was adopted as the base year for the calendar, instead of 46 BC.
Christmas was adopted to coincide with what was originally the winter solstice, to conflict with pagan celebrations of the "birthday of the unconquered sun".
Christmas celebrates the birth of Jesus, but is not in fact His actual birthday, a day which remains undetermined (even as to its year, as that was probably 4 or 6 BC, not 1 AD).
In Rome, at the time the calendar was finally regularized by Julius Caesar (46 BC), the winter solstice fell on December 25 in most years (in Rome nowadays, it falls on December 22 in most years). The slippage from Dec. 22 to Dec. 25 happened between 46 BC and 325 AD, the date of the first Council of Nicaea, which adopted the dates of Easter according to the date of the Spring equinox in that year. The current (Gregorian) calendar was regularized to 325 AD, and because the date of Easter had been set by that council, that year was adopted as the base year for the calendar, instead of 46 BC.
Christmas was adopted to coincide with what was originally the winter solstice, to conflict with pagan celebrations of the "birthday of the unconquered sun".
Christmas celebrates the birth of Jesus, but is not in fact His actual birthday, a day which remains undetermined (even as to its year, as that was probably 4 or 6 BC, not 1 AD).