If you were raised in a Christian country or have learned anything about Christianity, you will know that on December 25 Christians celebrate the birth of Jesus Christ.
You will also know that our calendar system separates the years into two eras – before Christ (BC) and Anno Domini (AD), or “in the year of the Lord”. But years change on January 1, rather than December 25, so what gives?
First off, it is not entirely clear when Jesus was born. The date is not mentioned in any of the Gospels, and accounts conflict with each other. The Gospels of Matthew and Luke, written a generation after Jesus was born, conflict in terms of geography and time. The Gospel of Matthew suggests that his birth took place during the reign of King Herod, while in Luke’s version of events Jesus was born after Herod had died and his son Archelaus had been deposed, during the reign of Quirinius (Cyrenius).
Neither of these versions of events line up with the turn from BC to AD, or BCE to CE (before common era to common era) as many now term it. Herod died around 4 BCE in March or April, a few years before the date we now assign to Jesus’s birth. Meanwhile, the census that Mary and Joseph were traveling to (according to Luke, the Census of Quirinius) took place in 6 CE.
For the most part, historians place the birth of Jesus at around 6-4 BCE, favoring the connection to King Herod. This would fit well with the suggestion that the star the wise men/three kings followed could have been a comet that appeared in 5 BCE.
As for why we celebrate Christmas on December 25, that too is a little murky. The date began to be celebrated in the second century CE, but took a few centuries to become cemented in the Christian calendar. There have been suggestions that the festival was given this late-December date in order to coincide with pagan festivals around the solstice, but that isn’t clear either. According to one idea, known as “calculation theory”, the birth date of Jesus was unknown, and it was instead linked to the date of his death.
“In Jewish tradition, the date of conception of [a] holy person coincides with the date of death. Early Christians believed that March 25 was when Jesus was crucified,” Martinus Ariya Seta, lecturer at Universitas Sanata Dharma, explains in a piece for The Conversation.
“Based on this theological assumption, the calculation shows that Jesus’ conception also happened on March 25. This means, Jesus was born exactly nine months later, or on December 25.”
As for why December 25 was not considered the first day of the year, you can put that down to the fact that January 1 had been the official start of the new year since at least 153 BCE. Centuries before that, it had been March, but now for the most part we (arbitrarily) agree the new year begins in January in places that center their calendars around the birth of Jesus – although not in Ethiopia, where they also disagree what year it is.
