During the Christmas season, it’s hard to go anywhere without seeing stars hanging from street lamps and perched atop Christmas trees. Although the Star of Bethlehem appears just once in the Bible, in the Gospel of Matthew in the New Testament, it has become one of the holiday’s most important and enduring symbols. Yet astronomers are still puzzled by whatever might have inspired that aspect of the Christmas story.
As EarthSky.org’s Larry Sessions writes, it's clear to modern astronomers that the Star of Bethlehem behaved very oddly, if it existed at all. First of all, Jesus Christ almost certainly wasn’t born in December, so looking for its origins in the night sky this time of year isn’t the best place to start. Historians have long agreed that Christmas shares roots with the ancient Roman solstice holiday, Saturnalia, and that Jesus was most likely born in the spring when shepherds would be tending their flocks, Donna Vickroy writes for the Chicago Tribune. In fact, Christmas only takes place on December 25 because of the Roman Emperor Constantine, who moved the holiday in order to coincide with the shortest night of the year.
While the Bible says that the three Magi were led to Jesus’ birthplace by a star in the sky, Art Maurer, the director of Joliet Junior College’s Trackman Planetarium, tells Vickroy that that explanation doesn’t quite jibe with the rest of the story. "The Magi came from Persia, which meant they traveled 900 miles west. So they didn't see a star in the east," Maurer tells Vickroy.
Some have suggested that the magi might have actually followed a bright meteor, comet or even a supernova, but as Joe Rao writes for Space.com, there are several problems with these theories as well. First, meteors may be strikingly bright, but they burn up in a flash when entering the Earth’s atmosphere, meaning the magi would have needed something a bit longer-lasting to chart their travels. A comet is a strong possibility, as Halley’s Comet was visible in 11 BC - a few years before when some historians think Jesus may have been born - but ancient astronomers often considered them bad omens, not good ones. And while a supernova would have certainly been a dramatic sight, there is no historical record of a bright nova at that time, Rao reports.
There’s one other possibility: it could have been a visible planet, like Jupiter. According to Maurer, Jupiter was in retrograde at the time, which means it would have appeared to travel east as it rose in the sky each night. Not only that, but ancient astronomers considered it the king planet, and its appearance in the Leo constellation might have been pretty significant for people who saw meaning in the movements of the stars and planets, Vickroy writes.
Historians will never know exactly what inspired the story of the Christmas Star, but like most symbols, the final meaning comes down to you.