A. Winter solstice
B. Nine months after Easter
C. In bible
D. Older calendars
Details of Why is Christmas on December 25th:
The Catholic Church established Christmas in an attempt to commemorate Jesus’ birthday, however, there is no official date for this celebration some people observe it in January and April instead. Since the pagans celebrated the solstice on December 25th, in the year 336, they chose to celebrate it on that day instead of the pagan holiday, which led to a happier conversion.