There are two main explanations for why Christmas is observed on December 25.
Many (but not all) Christians in today’s world observe Christmas on December 25. But why was this day chosen, given that we do not know with surety when Jesus was born?
There are two main explanations for why Christmas is observed on December 25. One theory, sometimes referred to as the “history of religion” theory, contends that one or more heathen festivals were replaced by Christmas. The alternative hypothesis, also known as the “computation” or “calculation” hypothesis, contends that early Christians calculated in some way to determine that December 25 was Jesus’ birthdate.
Both ideas could be accurate. According to Philipp Nothaft(opens in new tab), a scholar at the University of Oxford’s All Souls College whose work examines the history of astronomy and chronology, “the two theories are not mutually exclusive. The timing of Christmas has been studied and written about by Nothaft.
It’s uncertain precisely when and why some Christians began observing Christmas on December 25.
The chance that Christmas replaced the Sol Invictus feast, which was celebrated in the Roman Empire on December 25, is raised by ancient documents. In addition, a multi-day pagan celebration dubbed Saturnalia took place in the middle of December.
There are a few issues with this so-called history of faith hypothesis, though: Paul Bradshaw(opens in new tab), a retired professor of theology at the University of Notre Dame, speculated that Christians may have been commemorating Jesus’ birthday on December 25 before the Sol Invictus feast was established in an essay that was included in the book “The Oxford Handbook of Christmas(opens in new tab)”. (Oxford University Press, 2020).
Nothaft concurred. He wrote in the email, “A lot depends on when 25 December became the occasion of a Roman feast connected with [Sol Invictus]. Since [Emperor] Aurelian dedicated a new sanctuary to Sol Invictus in Rome in AD 274, most scholars would likely concur that this cannot possibly be older than that year. Nothaft endorsed this. “A lot depends on when 25 December became the occasion of a Roman feast connected with [Sol Invictus,” he wrote in the email. Most scholars would likely agree that this cannot possibly be earlier than AD 274, as [Emperor] Aurelian consecrated a new sanctuary to Sol Invictus in Rome.
We don’t know enough about this feast to be able to make statements with confidence, Nothaft continued. Another concern is whether the feast was important enough for early Christians to choose that day as the day of Jesus’ birth. Nothaft continued, “We don’t know enough about this feast to be able to make judgments with certainty. Whether the feast was significant enough for early Christians to select that day as the birthdate of Jesus is another question.
According to David Allen, a scientist at the Anglo-Australian Observatory, Dec. 25 is also “the date on which the Northern Hemisphere observers are first able to detect the northward movement of the sun” following the winter solstice.(opens in new tab). Allen pointed out that the discovery of this movement might shed light on why the celebration was conducted on this particular day.
The second theory, known as the computation hypothesis, contends that the earliest Christians computed the birthdate of Jesus by adding nine months to the day they believed to be the day of his gestation. One explanation is that some of the first Christians thought Jesus was crucified on March 25, and they added nine months to get December 25. According to Bradshaw, this indicates that the earliest Christians believed that the date of Jesus’s execution was the day of his creation.
A third-century writing on a monument that provides estimates for when Easter should be observed and has an etching on it indicating that Jesus was executed on March 25 in the year 29, Bradshaw wrote in his article, is one piece of proof for this theory. (Scholars tend to think that Jesus, who died at age 33, was born around 4 B.C.)
The computation theory has a flaw in that it’s uncertain why early Christians would choose March 25 as the day of both Jesus’ birth and crucifixion, according to Bradshaw.
Bradshaw wrote in an email to Live Science, “There is uncertainty surrounding both ideas, but I do believe the computation theory has a small edge. “There is uncertainty surrounding both ideas, but I do believe the computation theory has a small edge,” Bradshaw stated in an email to Live Science.
According to Nothaft, it’s conceivable that both ideas are accurate. According to him, the custom of celebrating Christ’s birth on December 25 has origins that date at least to the first century of the Christian era. If so, the computation theory in some form, along with Christian solar iconography, provides the most compelling justification for the genesis of this custom.