According to conventional wisdom, Christmas had its origin in a pagan winter solstice festival, which the church co-opted to promote the new religion. In doing so, many of the old pagan customs crept into the Christian celebration. But this view is apparently a historical myth—like the stories of a church council debating how many angels can dance on the head of a pin, or that medieval folks believed the earth is flat—often repeated, even in classrooms, but not true. William J. Tighe, a history professor at Muhlenberg College, gives a different account in his article "Calculating Christmas," published in the...