Bible scholar Colin R. Nicholl argues that the Star of Bethlehem was really a comet, a moving celestial object that was considered a type of star in ancient astronomy.
From What Kind of Astronomical Marvel was the Star of … | Christianity Today:
What evidence is there that the star was a comet?
The star appeared suddenly and was visible for over a year, something that makes sense only if it were a supernova or a great comet. That the star surprised the Magi with its impressive “rising” points strongly to it being a comet: Of all the celestial bodies, only comets behave in this manner. (Rising refers to the period when a celestial body re-emerges on the horizon after being hidden by the Sun.)