So when was Jesus born? Well certainly not December 25th. That was the feast of the Sol Invictus to the Romans. Or the winter equinox as we would call it, because the Sun always emerged victorious. It was also the time of the Saturnalia, a time of feasting and orgies. We eat Turkey and kiss under the mistletoe in memory of this. As to when was Jesus really born? Well, the Bible is all wrong. He probably wasn't even born in Bethlehem like it says. Probably outside Judea they say (for some reason-maybe the Roman census then). But the Bible says "And there were in the same country shepherds abiding in the field, keeping watch over their flock by night" which suggests it must have been towards the end of September. But some say he was obviously born in February, only because he clearly was an Aquarius. But people who believe in astrology say no. That's taking all "that" nonsense even a little to far for them.
The birth of Jesus was obviously an important event but there isn't really anything in the scriptures that indicates that we need to commemorate His birth annually. The exact date may have been lost to history. In the end it doesn't really matter when it happened. Christians can celebrate His birth whenever they want we don't need to know when it happened. The date has little impact on the more important aspects of christianity: forgiveness, justice, mercy, and faithfulness. I think a better question is can we be sure of the date of His death? Because passover/easter is a jewish festival and there is a much deeper significance to Jesus' death than His birth.