What Was the Christmas Star?

Was it a comet? A supernova? A planet? Or some otherwordly phenomenon? Everyday Einstein examines the possibilities.

Lee Falin, PhD
3-minute read
Episode #125

According to Biblical accounts, 2,000 years ago something appeared in the sky which led a group of wise men to Jerusalem to see the birth of the new king of the Jews.

But what was this bright light in the heavens? Let’s take a look at some of the prevailing theories. ;


Comets have been in the news quite a bit lately, what with the landing of the Rosetta mission on a moving comet. In case you haven’t heard by now, a comet is basically a big ball of dirt and ice flying through our solar system. They have really really long orbits around the sun, but like all orbiting bodies, they travel in predictable patterns. 

As comets near the sun, they start to melt, releasing a tail of dust and gas that stretches out a pretty long way, sometimes hundreds of miles. Comets can remain visible in the skies for several weeks. 

Nova and Supernova

Another common theory is that the event seen by the wise men was a star that went nova or supernova. A nova explosion occurs when two stars are in close proximity to one another. Over time, one star siphons off the stellar material of the other, building up to the point when it finally explodes. 

Supernova occur when a massive star experiences gravitational collapse. These events occur near the end of a star’s life and only happen with really, really big stars.

See also: Is it a Star or a Planet?


A nova explosion can cause a flash of light 500,000 times brighter than the light normally produced by the star. A supernova’s flash on the other hand can be more than 10 billion times as bright as normal star light.

Supernova are considerably more rare than novas, with only a couple having been recorded in history. Like comets, they can remain in the skies for several weeks. 

Planetary Conjunctions

Another common theory behind the Christmas Star is that of a planetary conjunction. Planetary conjunctions occur when two or more planets line up in the orbital plane. From Earth’s point of view, it appears as though these planets are moving together through the skies, or that they overlap one another. 

The more planets involved in a conjunction, the more rare it is. 

What Does History Say?

History tells us that all three of these events (novas, conjunctions, and comets), appeared near the time the Bible records for Christ’s birth. Some historians reject the notion that a comet was the sign, as comets were traditionally associated with rather gloomy prophecies, usually involving death and destruction. 

Novas are also commonly ruled out due to the fact that novas were relatively common and supernovas are similarly ruled out because none are known to have occurred at the correct time. 

The prevailing theory amongst historians is that the Christmas Star which led the wise men to Bethlehem was some type of planetary conjunction. 

In the movie The Mystery of the Christmas Star (commonly shown at planetariums this time of year), more details are given on this theory and the evidence supporting it. I highly recommend it to anyone interested in historical astronomy. 


So now you know a little more about some of the common theories related to the Christmas Star. 

If you have a question that you’d like to see on a future episode, send me an email at everydayeinstein@quickanddirtytips.com. If you liked today’s episode, you can become a fan of Everyday Einstein on Facebook or follow me on Twitter, where I’m @QDTeinstein.

Comet and star decoration images courtesy of Shutterstock.

About the Author

Lee Falin, PhD

Dr. Lee Falin earned a B.S. in Computer Science from the University of Illinois, then went on to obtain a Ph.D. in Genetics, Bioinformatics, and Computational Biology from Virginia Tech. 

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