I've read Molnar's book, don't think too highly of it. Astrologers in those days did not confuse planetary conjunctions with stars. A regular phenomenon like a bright Venus just before or after inferior conjunction with the sun, they might have referred to that as a star (evening star, morning star) as we still do; but a conjunction of planets would not have been termed a star, nor would it have looked like one for very long. And they certainly weren't referring to Venus.
Meanwhile the Chinese astrologers recorded a "hui-hsing" or broom star, perhaps a nova or supernova, in 5 BC. It remained visible for about 70 days (an unusually long period) and unlike most that were termed hui, there was no motion to it. If the records are accurate about its lack of motion and its duration, it wasn't a comet, yet it was classified as hui-hsing. In the official history, Chin-Shu, the term is defined: "Its body is a sort of star, while the tail resembles a broom." Also, a hui is a temporary star (or comet) that points in one direction. Nevertheless, the hui of 5 BC did not behave like a comet. IMO that's the one that merits a closer look.
The more interesting question, for me, was how this story of Magi locating the Messiah by astrological means, ever made it into the Holy Bible. Astrology being frowned upon in the Church.
"The more interesting question, for me, was how this story of Magi locating the Messiah by astrological means, ever made it into the Holy Bible."
Who says they used astrology? "A star shall rise out of Jacob" isn't anything that needs interpreting by an astrologer. And who says the wise men were astrologers?
They might only have read the prophecy in Numbers, they might have been Jewish; all the text says is that they were "wise men". ("Magi" covers a lot of territory, and is in any case a Greek translation of a Hebrew word in Matthew.)
If the information in the New Testament is accurate it would not have been something like a supernova at all. The key is that the Magi saw something in the sky that was in plain sight but wasn't readily visible (understandable) to most people -- including King Herod and his scholars. This would seem to clearly indicate that it was some kind of celestial event that looked quite ordinary to most people but was extraordinary to someone who had a thorough understanding of the night sky.
Because the Magi were astromonist instead?