Many people celebrate Christmas. Even if you’re not religious, it’s hard to escape the nativity scenes and carols reminding us of that “silent night” long ago.

But the occasion that takes every December by storm isn’t lost on the rest of the year. In fact, every time you write a check, file your taxes, book a reservation, or simply make an appointment, it’s there too.

Whether it’s 2012, 2013, or 2020, we’re subtly reminded that the very number of the year is established by something that took place over two millennia ago. The years, decades, and centuries of human history are all marked by one event: the birth of Jesus Christ.

The Birth of Jesus and the Gregorian Calendar

Though some cultures use a different calendar, the most widely accepted scheme today is the Gregorian calendar. In the sixth century AD, Christian scholars proposed numbering the years by using the birth of Jesus of Nazareth as a starting point. By the end of the eighth century the proposal was widely accepted.

The era before Jesus’ birth is known (oh-so creatively) as BC, or “Before Christ.” The era that follows (our current era) is referred to as AD, which comes from the Latin term Anno Domini, meaning “in the year of the Lord.”¹

So if Alexander the Great was born in 356 BC, he was born 356 years before the birth of Jesus. And to tell someone that you were born in 1992 is to say you were born 1,992 years after Jesus.

The Birth of Jesus and Year Zero

This all begs an interesting set of questions: How do we know when Jesus was born? Are we sure we’ve gotten it right? Exactly when was Jesus born?

For starters, we must recognize that in this date system there is no year zero. Early Christians who created the calendar based on Jesus’ birth established that the year immediately preceding the birth was 1 BC and the year immediately following it was AD 1.

So was Jesus born exactly halfway between 1 BC and AD 1? Well, it’s not that easy to figure out.

In fact, most scholars now agree that Jesus was probably born between 7 and 4 BC. In the early Middle Ages, when the Christian monk Dionysius Exiguus tried to calculate the year of Jesus’ birth and consequently developed our date numbering schema, he was off by a few years.²

The Birth of Jesus and the Gospel of Matthew

Why do scholars think Jesus was born between 7 and 4 BC? First off, one of the earliest historical documents to record Jesus’ birth says it took place during the reign of Herod the Great, the Roman ruler over Judea.³

According to the Gospel of Matthew, magi—wise men—came to Judea to visit the baby Jesus. When Herod heard a rumor from the magi that a “king” had been born in the town of Bethlehem, he was jealous. Wanting to dispose of any potential challenges to his authority, Herod asked the magi exactly when the baby was born. Then, based on the information they gave him, he secretly ordered the slaughter of all boys ages two and younger in Bethlehem.⁴

Going off the details of this decree, we can see that the magi probably visited Jesus when he was one or two years old, not while he was in the manger as is traditionally thought.

Shortly after this, Herod the Great died. This is where other ancient historians are helpful. From the Jewish historian Josephus and other sources, we know that Herod the Great died in 4 BC.⁵ Therefore, Jesus was certainly born before 4 BC, possibly as early as 7 BC if we allow for a year between the magi’s visit and Herod’s death.

Unfortunately, the Christian monk Dionysius did not have access to the sources and information modern scholars use. As a result, he miscalculated Herod the Great’s reign by a few years. But his mistaken setting of Jesus’ birth, notes New Testament historian Craig Blomberg, “eventually became so well entrenched that changing the calendar proved impossible.”⁶

The Birth of Jesus and the Gospel of Luke

The Gospel of Luke provides additional historical context: “In those days Caesar Augustus issued a decree that a census should be taken of the entire Roman world. (This was the first census that took place while Quirinius was governor of Syria.)”⁷

Luke’s account goes on to describe the familiar story of how Joseph and Mary traveled to Bethlehem for the census, which is how they came to be there for Jesus’ birth.⁸

However, there is a problem. Other ancient sources list Quirinius as governor of Syria later than the time period we are discussing, placing it between AD 6 and 9 instead of during Herod’s reign.

Did Luke get his rulers wrong? Maybe. But additional Roman records provide another possibility. Other sources “also speak of Quirinius leading military expeditions in the eastern provinces of the Roman Empire a decade earlier in a manner most naturally explained if he held some official post in Syria.”⁹

Indeed, two other ancient inscriptions have been found that seem to confirm this earlier office for Quirinius during 7–4 BC.¹⁰ In the end, we’re left with more evidence supporting the earlier date.

The Birth of Jesus and the Great Star

There is one more piece of evidence worth exploring. Matthew’s account describes an unusual star that shone in the sky not long after Jesus was born. Some accept this as a supernatural miracle. Others reject it as legend. Still others take a third position: perhaps there was a remarkable star in the sky that can be naturally explained.

According to astronomers, there was a conjunction of the planets Jupiter and Saturn from 7 to 6 BC in the constellation Pisces, which would have been unusually brilliant.¹¹ And in 5 BC, there are accounts of what may have been an exploding star, or supernova, in the sky.¹² While we cannot be certain that one of these physical phenomena explains the “Bethlehem star,” they are interesting possibilities.

The Birth of Jesus and December Twenty-fifth

Few doubt that Jesus of Nazareth was born between 7 and 4 BC. But there is one final question to explore: Did the birth take place on December twenty-fifth of one of those years?

Almost certainly not.

The actual day of Jesus’ birth is unknown, but Christians in the Roman Empire hundreds of years later began to celebrate it on December twenty-fifth or January sixth—days that coincided with Roman holidays and the winter solstice.¹³ And once that tradition began, the rest, as they say, is history.

The Birth of Jesus and Its Significance

Ultimately, what makes Jesus’ birth important is not the actual day or year it happened. What makes his birth significant is that it happened at all. Jesus’ birth sparked a revolution. And since then billions of people all over the world have celebrated a new era in history—the era of “Immanuel,” a Hebrew word meaning, “God with us.”