When I grew up, I was informed that December 25th was not the real birthday of Jesus—and it’s a historical fact that this date was simply adopted by the Church over a thousand years ago as a day to celebrate the nativity. This is partly because no one really knew the date—there just wasn’t enough information—and that seems reasonable knowing the accounts. But in the last few decades historians and astronomers have pieced together some amazing clues that give us a precise date that seems very likely. I was skeptical when I first heard this. But the evidence now seems very compelling.
Unlike finding the day of the year of Jesus birth, calculating the year of his birth may not be such an impossible task. It is pretty much agreed that based on the gospel of Matthew that the nativity must have happened a few years before the death of King Herod the Great. Furthermore, based on the details from Josephus and other Roman historians, we know that King Herod died in 4 BC. That would place the birth between roughly 7 to 5 BC. No, not the year zero—which we do not even count as a year—historians count the years as going from 1 BC to 1 AD. To narrow down when during these three years, we need to look at clues from two independent sources: Babylonian astrology, and the schedule of Jewish Priests serving at Herod’s new Temple.
THE STAR OF BETHLEHEM
Let’s begin with astrology—which two thousand years ago was the same thing as astronomy. Both the Babylonians and the Greeks watched the night skies with great interest and plotted and calculated the movements of the stars and planets. They also believed that these movements influenced world events. In 1999 Michael Molnar, an astronomer from Rutgers University, published a book—"The Star of Bethlehem”. The book gives the first really convincing explanation for what the “wise men from the east”—likely Persia—saw. Molnar goes into great detail describing how horoscopes were used by the Greeks, Egyptians, and Babylonians at the time to predict events, and especially royal births. Kings and emperors were given their horoscopes that could tell them they were destined for greatness from the day they were born. The signs that would indicate this were complex, yet very well established and written down. They also were specific about which constellations of the Zodiac represented which countries. The sign of Aries, the Ram, was known to correspond to the Levant, and especially Judea. The planet with the most royal implications was Jupiter. Certain positions of Jupiter with respect to the other planets, the moon, the sun, and the horizon, on a certain day, would give strong indicators that someone born on that day in that country was destined for royalty. And if more than one of these alignments were present the indications were very strong. The most important of these alignments were the following: the sun had to be in the constellation of that country, Jupiter was also in that constellation close to the sun, Jupiter was close to the moon, and the meeting of these happened close to the horizon at sunrise or sunset.
In the last decades computer programs have been created that can rewind the night sky back thousands of years to see exactly what it would have looked like at any time of any day from any place on earth. Molnar decided to run such a program back in time to look at the years between 10 and 4 BC to see if anything unusually royal appeared for the country of Judea, as seen from the Middle East. Lo and behold, two dates, and only two, appeared where all the indicators were present—and more. For those dates Jupiter and the Sun were both in Aries at sunset, and then sunrise. These two special dates also had the moon eclipsing Jupiter for a few hours! —something extra special that would really have excited any astrologer at the time watching the skies for signs. The dates were March 20th and April 17th, 6 BC. Others have later calculated that such a special event would occur only once in many thousands of years. These two dates are one month apart. That is because the moon in that time circled the earth to once again line up with Jupiter. The second time was at sunrise rather than sunset. The fact it happened twice would have confirmed to them that someone really special must have just been born. So now it seems that the early spring of 6 BC is a target for what astrologers from the east would have deemed a royal birth—one worth paying a visit to perhaps. And after they left to return home, Herod realized it had been nearly two years since they had first seen the “star”, and Herod was still alive—he died not long after in the spring of 4 BC. But do we believe that births and destinies align with the stars? Most today don’t. But many in that time did. And this celestial event happening in 6 BC is eerily spot on.
Let’s move to an independent check then on the monthly timing of the birth of Jesus to see if that might line up with the Month of Nisan—either March or April. That would certainly add weight to the idea that one of the Lunar-Jupiter occultations was an indicator of royal birth. But what can the schedules of priests working in the Temple tell us about the timing of the birth of Jesus? This unassuming clue comes from the gospel of Luke, where the foretelling of the birth of John the Baptist is described. His father, Zechariah, was a priest working in the Temple in his normal rounds when he saw an angelic vision predicting his son’s birth to Elizabeth, who had been barren. When he returned home, she became pregnant. Six months later she was visited by Mary, who had just been told she had become pregnant. Nine months later Jesus was born. That means 15 months or so after Zechariah left the Temple, Jesus was born.
Here is the key. It says Zechariah was of the priestly course (group) of Abijah. According to the book of 1 Chronicles King David had divided up the tribe of Levi into 24 groups to take turns working in the coming temple that Solomon was to build. Abijah is listed as course number eight. Josephus tells us that these 24 courses took turns working in the time of Herod’s Temple. Each group worked one full week, twice a year, in the order listed. But 24 times two makes 48 weeks, not 52 weeks in a year. Josephus tells us that at a few festival times, all the groups drew lots and took turns serving off and on those extra few weeks. This way no one group got stuck working the holiday shift every year. We are trying to figure out here which weeks of the year Abijah’s group, and thus Zechariah, would have served. That would give us starting point from which to add 15 or so months to the birth of Jesus—to see if that agrees with the dates the astrologers saw the moon eclipsing Jupiter.
There are still a number of possibilities with the priestly schedule though. Not only two different weeks of the year when Zechariah was serving, but two other possibilities—did the schedule restart every year on Nisan 1—the religious new year? Or did they cycle through continually from when the service first started up decades before? Several historians using other clues have back-calculated when the course of Abijah would have been serving in the Temple. Fortuitously, in the year 8 BC, Zechariah would have finished his service either near the end of May or near the end of November—whether the schedule restarted every year or cycled differently as it adjusted year to year. If Zechariah saw his angelic vision in late May or November and then returned home, then either June or December of 8 BC would be the month for the conception of John the Baptist. Adding 15 months then lands us in either September of 7 BC or March of 6 BC. The latter one agrees with a March 20th date for the eclipse of Jupiter by the moon, witnessed by the magi in the east. Thus, additional independent evidence is added in favor of the March eclipse date.
We cannot say for sure that March 20th is the exact date. But amazingly when you place this date into a conversion calculator for Julian to Jewish Calendars, in 6 BC it falls on Nisan 1—the Jewish religious New Year—when things are to begin anew. Just a coincidence? That’s also a time in spring when sheep often give birth to lambs. Such lambs were used one year later in Passover meals on the 15th of Nisan. During lambing season shepherds watched for these births to make sure they happened safely. Even if that means they were out watching their flocks by night.