In the run up to Christmas, carols fill the air. Many have an astronomical twist, singing of the “Christmas Star” from the story of the nativity. Described in the Gospel of Matthew, the star guided the three wise men to the cradle of the young baby Jesus in a manger in Bethlehem.
Most Biblical scholars agree Jesus was born between 6 and 4 BCE. It’s not known what time of year he was born, but those scholars suggest it was most likely in April or May.
The choice of December 25 to celebrate Jesus’ birth came centuries later, and is tied to the date of the winter solstice in the Roman calendar, when the northern hemisphere experiences its shortest day.
Many Biblical scholars also view the Christmas Star, which is also known as the Star of Bethlehem, as pious fiction – a symbolic story meant to establish the messianic status of Jesus, rather than a real event. But what if it was some sort of astronomical phenomenon?
Astronomers have long pondered this question and proffered some potential explanations. Perhaps historical records from across the globe might reveal what the Magi saw, and help to work out exactly when the events in the story happened.
If so, what could the Christmas Star have been?
A bright comet?
The idea that the Christmas Star might have been a bright comet has a long history. The Adoration of the Magi, painted in 1305 by Giotto di Bondonne, featured a comet in pride of place as the Christmas Star.
Giotto’s cometary Christmas Star was inspired by the bright apparition of comet 1P/Halley, which the artist observed in 1301. So could 1P/Halley, or another bright comet, have been the Star of Bethlehem?
Comet Halley orbits the Sun every 74 to 79 years, so it has made regular spectacular appearances throughout human history. It was widely observed across the planet in the year 12 BCE – too early to be the star of the Christmas Story.
What about other comets? Well, astronomers and historians have dug through the records of comets seen by cultures across the globe, and only one comet stands out as a potential candidate for the story.
A comet is recorded in ancient Chinese records, seen in 5 BCE. That comet was flagged as a potential Star of Bethlehem in the late 1990s, with the Chinese observations noting the comet was visible for more than 70 days.
Recently, the idea that the comet of 5 BCE could have been the Christmas Star has leapt back into focus, thanks to research that suggests the comet of 5 BCE followed an unusual path through the inner Solar System, and made a remarkably close approach to Earth. In that scenario, the comet would have appeared almost stationary in the sky for a lengthy period of time – all the hallmarks of the star from the Nativity.
Read more:
Stories from the sky: astronomy in Indigenous knowledge
A supernova?
Some astronomers have argued a supernova would be an ideal candidate for the Christmas Star. Supernovae are immense explosions caused either by massive stars reaching the end of their lives, or white dwarfs (the remains of a star like the Sun) suffering a terminal case of stellar indigestion as they devour a companion.
Both types of supernova are a spectacular sight – outshining the combined light of all other stars in their host galaxies for a period of several weeks. As a result, supernovae that explode within our own galaxy, the Milky Way, can become highly prominent – sometimes even becoming bright enough to be visible in daylight.
ESA/Hubble & NASA, A. Riess and the SH0ES team. Acknowledgment: Mahdi Zamani, CC BY-NC-ND
Once again, astronomers pored over ancient records, looking to find potential observations of a bright supernova that would fit with the nativity story.
Reports from Korea to Palestine described a new star in the night sky – an object that was most likely a supernova. It is estimated to have peaked in brightness around February 23 in 4 BCE, in the constellation of Aquila, the Eagle.
This could be a good fit. In February, Aquila rises in the east in the early morning, a few hours before sunrise. As such, a bright supernova in that part of the sky would be a spectacular morning star high in the eastern sky – remaining bright for several weeks before fading away, never to be seen again.
A planetary conjunction?
In recent years, the most common claim for the Christmas Star is that it was actually a planetary conjunction. This is when planets get very close to one another in the sky, as happened back in December 2020 with the “Great Conjunction” of Jupiter and Saturn.
This idea has been raised, on and off, for more than four centuries, since the great scientist Johannes Kepler suggested in 1614 that the triple conjunction of Jupiter and Saturn in 7 BCE could have triggered a nova that became the star in question.
The 7 BCE conjunction was far from spectacular, with Jupiter and Saturn separated by more than a degree. But just a few years later, in 2 BCE, there were a striking series of conjunctions between the brightest planets in the sky: Jupiter and Venus.
Could one of those conjunctions have been the Christmas Star? It seems unlikely. The Venus–Jupiter conjunctions would have been seen in the evening sky, low in the west – making them a poor fit to the nativity story.
Peter Lieverdink, CC BY-NC-ND
Or perhaps, there was no star?
None of the explanations put forward to date seem to perfectly match the story passed down through the centuries.
So it might just be the case that there simply was no Christmas Star – that the story truly is a pious fiction.
But it is still worth considering what it might have been; at the very least, it can teach us about some of the many wonders of the universe. And who knows what more we will discover in the years to come – we certainly haven’t heard the last speculation about the true nature of the “Star of Wonder”.