Researchers believe the Roman Catholic Church settled on Dec. 25 for many reasons, such as that date's ties to the winter solstice and Saturnalia, a festival dedicated to the Roman deity Saturn. By choosing this day to celebrate Jesus' birthday, the church could co-opt the popular pagan festival, as well as the winter celebrations of other pagan religions.
But nobody really knows exactly when Jesus was born.
Some scholars think that he was born between 6 B.C. and 4 B.C., based partly on the biblical story of Herod the Great. Not long before Herod's demise, which is believed to have occurred in 4 B.C., the ruler of Judea supposedly ordered the death of all male infants who were under the age of two and lived in the vicinity of Bethlehem, in an attempt to kill Jesus.
But historians disagree about Herod's actual year of death. What's more, the horrific mass infanticide is legend, not fact, Reza Aslan, a biblical scholar and author of "Zealot: The Life and Times of Jesus of Nazareth" (Random House, 2013), told PolicyMic.
To pinpoint Jesus' birth year, other scholars have tried to correlate the "Star of Bethlehem," which supposedly heralded Jesus' birth, with actual astronomical events. For example, in a 1991 article in the Quarterly Journal of the Royal Astronomical Society, astronomer Colin Humphreys proposed that the fabled star was actually a slow-moving comet, which Chinese observers recorded in 5 B.C.
Scholars also debate the month of Jesus' birth. In 2008, astronomer Dave Reneke argued that Jesus was born in the summer. The Star of Bethlehem, Reneke told New Scientist, may have been Venus and Jupiter coming together to form a bright light in the sky. Using computer models, Reneke determined that this rare event occurred on June 17, in the year 2 B.C.
Other researchers have claimed that a similar conjunction, one between Saturn and Jupiter, occurred in October of 7 B.C., making Jesus an autumn baby.
Theologians have also suggested that Jesus was born in the spring, based on the biblical narrative that shepherds were watching over their flocks in the fields on the night of Jesus' birth — something they would have done in the spring, not the winter.