There is no way to know the exact day on which Jesus was actually born. However, Jesus’ birth has been celebrated on December 25 since the early fourth century, when most of the Roman Empire adopted the Christian religion. It replaced the mid-winter Roman festival of “the birth of the sun god,” which was celebrated just after the winter solstice.
Christmas is not just one day, but an entire season.
In the modern secular world the “Christmas Season” (for shopping, decorating, parties, music, etc.) used to begin just after Thanksgiving Day, but now seems to begin just after Halloween, if not before! December 26 already begins the “after-Christmas” sales, and Christmas decorations are often removed before New Year’s Day!
In Christian traditions, however, the “Christmas Season” properly begins with Christmas Eve (after sunset on December 24). The Christmas Season ends on the Feast of the Baptism of the Lord, which normally falls on the Sunday following the Epiphany.
So plan to celebrate the Birth of Christ throughout the entire Christmas Season. (10:4)