Star of wonder

Was the Star of Bethlehem a natural astronomical object? If it was supernatural or preternatural, why does Scripture call it a star? Two observations:

i) Sometimes the word "star" is used metaphorically, to stand for something else (e.g. Num 24:17; Judges 5:20; Isa 14:12; 2 Pet 1:19; Rev 1:16).

ii) Perhaps more to the point, in Matthew's account the object is called a "star" four times (2:2,7,9,10). The first time the object is introduced to the reader, it is the Magi rather than the narrator who uses that designation. It's initially called a star because it appears to be a star-like object to the Magi, when they saw it for the first time. That's their phenomenological impression. 

The narrator then picks up on their designation. The probable reason he calls it a "star" is not because he regards the object as a natural astronomical phenomenon, but in consistency with the Magi's usage. Because they classify the object as a star, because the phenomenon is introduced to the reader by quoting the Magi's description, the narrator simply continues with that designation. It would be confusing to the reader if the narrator suddenly used a different descriptor. His usage conforms to the usage of the Magi, because it has the same referent. He and the Magi are talking about the same thing–whatever that is. To shift from one designation to a different designation in the middle of the story would obscure the reference.