Question: "What was the star of Bethlehem?"
Answer: The Star of Bethlehem is associated with the visit of the magi (wise men) from the East as recorded in Matthew 2:1-12. The text implies the Star appeared only to the magi in the East (the “East” most likely being the area of Persia, or modern-day Iran). There is no biblical record of anyone else observing this phenomenon. The magi saw something in the heavens that alerted them the Jewish Messiah was to be born (in Matthew 2:2 the magi refer to the star as being “His star”). The Star prompted them to travel to Jerusalem, the Jewish capital. This would be the logical place to start looking for the birth of the King of the Jews.
When the magi were told that the Messiah would be born in Bethlehem, not in Jerusalem, they left. Herod "sent them to Bethlehem" (Matthew 2:8). Upon their leaving Herod, the Star that appeared to them in the East re-appeared and led them to the place Joseph and Mary were then staying (Matthew 2:9). Modern portrayals of the nativity scene show the wise men visiting Jesus on the night of His birth. That is likely not what truly occurred. The fact that Herod had all male babies two years old and under in Bethlehem killed (Matthew 2:16) indicates that up to two years had passed since the wise men saw the star - and possibly since Jesus' birth.
The Greek word translated "young child" (Matthew 2:9) can mean anything from a newborn infant to a toddler - Jesus may have been as young as one day old when the magi visited, or He could have been as old as two years. Joseph and Mary almost surely stayed in Bethlehem until Mary could travel again. In fact, they probably stayed there for the 40 days necessary to complete Mary's purification. From Bethlehem, they could easily make the five-mile trip to Jerusalem for the sacrifice for Mary's purification (Luke 2:22). The fact that the magi came to a "house" (Matthew 2:11) rather than the stable makes sense because Joseph naturally would have moved his family to a more protected place as soon as possible - the morning after Jesus was born, in all probability.
The Greek word that is translated “star” in the text is the word aster, which is the normal word for a star or a celestial body. The word is used 24 times in the New Testament, and most of the time it refers to a celestial body. It can be used to denote angels, as in Revelation 12:4, where it is used to describe the fallen angels who followed Satan’s rebellion. However, aster is used in the sense of "a celestial body" in Matthew 2. Basic rules of biblical interpretation state that we should take the normal sense of the word unless there is compelling evidence to suggest otherwise. In fact, many interpreters have done as much by suggesting a natural explanation for the Star of Bethlehem. Their suggestions range from calling it a supernova or a comet to saying it was the conjunction of several celestial bodies which provided a brighter-than-normal light in the sky.
However, there is compelling evidence to suggest that the Star of Bethlehem was not a natural stellar phenomenon, but something unexplained by science. That evidence lies in what we've noted above. First, the fact that the Star only appeared to the magi indicates that this was no ordinary star. Furthermore, the magi traveled to Jerusalem because they were looking for the sign of the Messiah. How would Persian magi know about the Jewish Messiah? They would have been exposed to the writings of the Jewish prophet Daniel, who had been the chief of the court seers for Persia. In Daniel 9:24-27 is a prophecy that gives a timeline for the birth of the Messiah. Also, they may have been aware of the words of the pagan prophet Balaam (who was from the town of Pethor on the Euphrates River near Persia) in Numbers 24:17. Balaam's prophecy specifically mentions a “star coming out of Jacob.” Finally, celestial bodies normally move from east to west due to the earth’s rotation, yet this Star led the magi from Jerusalem south to Bethlehem. Not only that, but it led them directly to the place where Joseph and Mary were staying, stopping directly overhead. There is no natural stellar phenomenon that can do that.
So, if the normal usage of the word “star” doesn’t fit the context, what does? What we likely have in Matthew 2:1-12 is a manifestation of the Shekinah Glory. The Shekinah, which literally means “dwelling of God,” was the visible presence of the Lord. The most notable appearance of the Shekinah is recorded in Exodus 13:21. The Shekinah was the pillar of cloud that led the Israelites by day and the pillar of fire that led them by night. The Shekinah fits all of the biblical evidence available in Matthew 2:1-12. The Shekinah can appear to specific individuals, it can disappear and re-appear, it was seen in connection with Christ’s ministry (e.g., Matthew 17:5; Acts 1:9), and it can lead people to specific locations. It shouldn’t surprise us that God would use a miraculous sign to signal the advent of His Son, the Messiah, into the world.