Nobody knows when Jesus was really born. Neither the year nor the day of his birth is clear.
Only since the beginning of the 4th century was December 25th celebrated as Jesus’ birthday. Then why are we already celebrating on December 24th? Christmas?
December 24th
The reason why we celebrate Christmas on December 24th may be that a calendar day does not always begin at midnight, i.e. zero o’clock.
Rather, the old day ended at dusk and the new day dawned.
So when the sun sets around 4 p.m. on December 24th, December 25th begins according to this counting method and with it Christmas. Traditionally, many churches invite to the Christmas services at this time.
December 25th
December 25th was already a holiday for the Romans in honor of the “birth of the invincible sun”.
Some theories have it that the Fathers of the Church chose this day to introduce pagan winter solstice festivals into the Christian liturgy. After all, Christ is considered the “light of the world”. Another explanation for the date is of a Christian-religious nature: Even in ancient times it was believed that perfect people would not die at some point, but on their birthday.
With regard to Jesus, the idea prevailed that it was not his birthday that corresponded to the day he died, but the day on which he was conceived.
If one now assumes that the crucifixion took place on the equinox, on March 25th according to the then valid Julian calendar, and that this was the day of Jesus’ conception by the Holy Spirit, then the due date after ten months of pregnancy is the 25th December.