Ancient great conjunction
What about a mash-up of planets like the upcoming Great Conjunction of 2020? Could that explain the Star of Bethlehem?
When you rewind the motion of the planets — something that’s easy to do with observing software these days — you can see that several interesting conjunctions played out in the years around the life of Jesus. (A planetary conjunction happens when two planets make a close approach to each other in Earth’s night sky. The two objects aren’t actually near each other, though, they just look that way from our vantage point.)
In the year 7 B.C., Jupiter and Saturn had three conjunctions in the same constellation, Pisces. Because the planets move in their orbits at different speeds, and are located at different distances, sometimes they appear to pass one another in the night sky. They can also appear to hold still or move backward in the sky, which astronomers call retrograde motion. This trick is like passing a slower car on the highway. As you get close to the other vehicle, it seems to hold still beside you. Then, as you pull away, it drops backward. The same thing happens as Earth zips around the Sun much faster than the outer planets.
However, Jupiter is closer to the Sun than Saturn, so it also appears to move faster in our night sky.
So, if Jupiter and Saturn had three close conjunctions in a relatively brief period of time, it’s easy to imagine that ancient astronomers — really, astrologers — would have taken note. And they also likely would have ascribed some meaning to the event.
These same astrologers wouldn’t have had to wait long for an even more striking planetary encounter. Four years later, in the summer of 3 B.C., Jupiter and Venus met in an event that would have looked much like the upcoming "Christmas Star," also referred to as the Great Conjunction of December 2020.
On the morning of August 12 in 3 B.C., Jupiter and Venus would’ve sat just 1/10th a degree apart in the dawn sky. That’s one-fifth the diameter of the Full Moon. (The December 2020 conjunction between Jupiter and Saturn will have an identical separation, albeit in the evening sky.) That wasn’t the end of the show, either. Venus and Jupiter continued their dance over most of the next year before finally appearing to merge into a single star in June.