Adoration of the Magi by Florentine painter Giotto di Bondone (1267–1337).

I recall seeing a planetarium show around this time of year when I was a kid on a trip to the Newark Museum. Of course, we saw the planets and famous stars, but I remember that they showed us how Jupiter, Saturn and Mars were coming together and what it might have looked like above Bethlehem at the first Christmas.

The Star of Bethlehem was something I learned about as a kid in religious classes, and I saw it depicted quite literally above the creche that was under our Christmas tree. But I wasn’t that grown up when I began to wonder what star it was and why didn’t it have a scientific name.

I never got a good answer, and as I got older I discovered that there were several reasons why it was not an easy question to answer. First, there is uncertainty in the actual date of Christ’s birth. Second, the terminology used to describe celestial events 20 centuries ago are not what we use today.

Back then, any celestial object bright enough to be seen with the eye tended to be called a “star.” That is how meteors were described as “shooting” or “falling” stars. A comet was called a “hairy” stars. Novas would be called a “new” star. In this time before astronomy, even planets were viewed as “wandering” stars.

The painting Adoration of the Magi by Giotto di Bondone (1267–1337) shows the Star of Bethlehem looking like a comet above the Christ child. It is known that Giotto witnessed an appearance of Halley’s Comet in 1301 and that probably is what made him decide to depict it as a comet rather than a fixed star.

The Bible doesn’t say anything about a calendar date of the Nativity. Scholars look at references to people or events such as the reign of King Herod. We believe he died sometime between 4 B.C. and 1 B.C. by our present calendar. The Three Wise Men (Magi)  visited Herod just before he died and presumably the birth of Christ and the first appearance of the guiding star came sometime before that.

There is no evidence that Jesus was born in late December. A passage by Luke in the Bible –  “And there were in the same country shepherds abiding in the field, keeping watch over their flock by night” actually suggests that it was spring which was the time when shepherds in Judea were out at night tending the newborn lambs.

However, December 25 was the end of the week of the Roman festival of Saturnalia. Gifts were exchanged and homes, streets and buildings were decorated. Relatives often returned home for this holiday. The early Christians often used elements of pagan holidays in order o make the transition to Christianity more familiar and comfortable.

Those early Christians may have also chosen the date of the Saturnalia in order to avoid attention with their own celebration and so escape persecution. When Roman emperor Constantine officially adopted Christianity in the 4th century, the date of Christmas remained as December 25.

Christ’s birth also probably did not occur 2016 years ago. Our present numbering of years as AD or BC was conceived by the Roman abbot Dionysius Exiguus around 523 A.D. Dionysius placed 1 A.D. immediately following 1 B.C. and disregarded the mathematically required zero in between. We can’t completely blame him, since then in Europe zero was not considered a number. That makes our 3 B.C., actually –2, numerically speaking.

Dionysius also accepted a fairly common assumption of that time that Jesus was born in the 28th year of the reign of the Roman emperor Caesar Augustus. But Augustus was known in the first 4 years of his reign by his original name Octavianus, so that adds another possible error of 4 years.

Back to that star… Was there any unusual celestial occurrence between the years 7 and 2 B.C. that might have caught the attention of people or the Magi? I found four theories.

I like the comet theory. Either a comet or nova was seen by Chinese and Korean stargazers in about 5 BC. It was observed for over seventy days with no movement recorded. That would have given the Magi time to travel. But it would be odd to choose a comet to follow because in that time comets were seen not as good omens but as omens of bad things to come.

Halley’s Comet appeared in August and September in the year 11 BC, but that seems a bit too late to be what the Wise Men saw.

Another theory is that it was a nova or supernova outburst: That would be something that appears anew but leaves no trace for us to find in the future. Although their names imply a new creation, these spectacular objects are in reality dying stars, although they are new (but temporary) additions to the nighttime sky. Really bright novas are visible usually a few times in a lifetime. The most recent one I found listed appeared in August 1975 not far from the bright star Deneb in the constellation Cygnus.

There was one nova that appeared in the spring of 5 B.C. according to Chinese records, but it is described as not very prominent.

The least likely theory is that it was a meteor. But meteors move across the sky in seconds and are not candidates of a guiding light that could lead the Magi halfway across the Orient to Bethlehem.

The Comet of Bethlehem seems the best possibility. One might have been visible to the naked eye for a few weeks predawn or at dusk and its head and tail may have been a kind of compass pointer.