It is to celebrate the birth of Christ, but Chirst was born in the Spring time, Luke 2:8-21
[FONT=&]“And in the same region there were shepherds out in the field, keeping watch over their flock by night.9 And an angel of the Lord appeared to them, and the glory of the Lord shone around them, and they were filled with great fear.10 And the angel said to them, “Fear not, for behold, I bring you good news of great joy that will be for all the people.11 For unto you is born this day in the city of David a Savior, who is Christ the Lord.12 And this will be a sign for you: you will find a baby wrapped in swaddling cloths and lying in a manger.”13 And suddenly there was with the angel a multitude of the heavenly host praising God and saying,[/FONT]
14 “Glory to God in the highest, and on earth peace among those with whom he is pleased!”
[FONT=&]15 When the angels went away from them into heaven, the shepherds said to one another, “Let us go over to Bethlehem and see this thing that has happened, which the Lord has made known to us.”16 And they went with haste and found Mary and Joseph, and the baby lying in a manger.17 And when they saw it, they made known the saying that had been told them concerning this child.18 And all who heard it wondered at what the shepherds told them.19 But Mary treasured up all these things, pondering them in her heart.20 And the shepherds returned, glorifying and praising God for all they had heard and seen, as it had been told them.[/FONT]
21 And at the end of eight days, when he was circumcised, he was called Jesus, the name given by the angel before he was conceived in the womb.”
The Shepherds would take the sheep out in the spring time and bring them back at the beginning of October, before the snow covered the greenary. Another tradition that is not Biblical, are the three wise men, the Bible never mentions anything about three wise men. What it does say is there were three gifts in Matthew 2:11 “And going into the house, they saw the child with Mary his mother, and they fell down and worshiped him. Then, opening their treasures, they offered him gifts, gold and frankincense and myrrh.”
There is never a mention of three wise men or three magi. More traditions of men that are not Biblical, but people say it like it is Gospel truth. Trying to figure out the exact year is another story, but there is Biblical marking that history tells us when it was. So if you would like to know you can do a historical and Biblical search that will give you a good source for the date.