The star is the sign that lead the Magi to the Christ Child. Matthew 2:1 9b-11
After Jesus was born in Bethlehem in Judea during the time of King Herod. Magi from the East came to Jerusalem and asked "Where is the One who has been born King of the Jews? We saw his star in the East and have come to worship Him" .
They went on there way and the the star they had seen in the East went ahead of them until it stopped over the place where the child was...they saw the child with his mother Mary and they bowed down and worshipped him. They opened their treasures and presented him with gifts of gold and of incence and of myrrh.