This time of year, a popular question astronomers get asked is, "What was the Star of Bethlehem?" This blog normally steers clear of religious issues altogether. After all, (1) I am an astronomer, not a theologian, (2) I would hope that this blog can reach to any person, regardless of their beliefs, and (3) my beliefs are just that -- mine -- and not necessarily yours. But, since the question comes up and since the Star of Bethlehem is central to many people's celebrations this time of year, I thought I would at least touch on the issue.
The fact is that astronomers have no good explanation for the Star of Bethlehem as described in the Gospel of Matthew. Different ideas have been put forth: a conjunction of the planets Mars, Jupiter and/or Saturn in 7/6 B.C., a comet, a supernova, and even more exotic astronomical phenomena. A search for "Star of Bethlehem explanation" on Google or your favorite search engine will being up a plethora of pages with highly-variable quality of scholarly explanations for each of these. In spite of this, none of the proposed explanations fit all of the passages from the Bible. Perhaps in the years between the Nativity and the writing of the Gospels the event became a little garbled or exaggerated, or perhaps the narrative was invented, or perhaps there is no physical explanation for what appeared in the sky.
So, I have no definitive answer to what the "Star of Bethlehem" might have been, and anybody who claims to know a definitive physical explanation is probably overstating their case. If you are interested in this, I would suggest that you read some of the materials on the web or elsewhere and form your own opinion. Like many religious matters, the Star of Bethlehem must remain an issue of faith, not of science.