From the early pages of the Gospel of Matthew to holiday-greeting cards and carol scores of today, three Magi leaving Jerusalem and following a star hovering over Bethlehem has become one of the icons of the Christmas season.

Some ascribe the appearance of the "star" to a miracle. But as far back as the early 1600s, when Johannes Kepler offered up a cosmic candidate, astronomers have suggested a series of astronomical explanations for the apparition, ranging from comets to planetary conjunctions.

In modern times, the hunt has been aided by computer programs that can reproduce the night sky as viewed from any spot on Earth for thousands of years either side of today's date.

Ah, but which year to visit, let alone which days?

IN PICTURES: O Christmas Tree

Scholars and amateurs alike who have tackled the Star of Bethlehem challenge note that they have to make educated guesses based on records that ancient historians kept of officials. Among them, King Herod, on whom, according to the Gospel, the Magi made a courtesy call en route to Bethlehem and someone the trio carefully avoided after visiting a young Jesus and his parents.

Indeed, Herod's death has become a marker for estimating when Jesus was born. According to the Gospel account, Herod died shortly after decreeing, in a fit of paranoia, that children 2 years old and under be killed in Bethlehem and the surrounding area. Many scholars argue that Herod died in 4 B.C., which would put Jesus's birth year somewhere between 6 and 4 B.C. Others have argued for a 1 B.C. demise for Herod.

That puts astronomers in the temporal ballpark.

Among the early contenders for "star" status:

• A comet. Astrologers back in the day, also known as magi in the Near East, often saw these as harbingers of a significant change coming to a kingdom, if not the world as they knew it. Halley's comet appeared in 12 B.C., according to Bakersfield College astronomy professor Nick Strobel. But that falls outside the presumed range of birth years for Jesus.

• A nova or supernova – different forms of exploding stars that suddenly appear in the sky with extraordinary brightness and then fade over ensuing months. Dr. Strobel notes that Chinese astrologers, who kept extraordinary records of the night sky, recorded a nova during the spring of 5 B.C. But if the star were a nova, Matthew's Gospel has it traversing the night sky far faster than astronomical distances, orbital mechanics, and three traveling Magi would allow.

• Conjunctions between bright objects in the night sky that appear to an observer to be very close to each another, although they remain quite distant. Astrologers viewed conjunctions as portentous. And astronomers have identified three that plausibly might have served as Matthew's star.

One involves three conjunctions between Jupiter and Saturn (considered wandering stars, back in the day) in 7 B.C. The two appeared as a close pair in the eastern sky in late May, and in the southern sky in late September and early December. Not exactly between 6 and 4 B.C., but given the uncertainties, maybe close enough.

Another involves a conjunction between the moon and Jupiter on April of 6 B.C. in which a new moon, dark from Earth's vantage point, temporarily obscures Jupiter. Unfortunately, the event happened during daylight hours,

Still another, if you pick a 1 B.C. demise for Herod, involves a conjunction between Venus and Jupiter in the eastern sky before dawn in August of 3 B.C., followed by a comparable conjunction the following June lower in the western sky. During both conjunctions, the two objects appear to merge. The June event occurred near Regulus, a bright star in the constellation Leo – a constellation astrologers associated with royalty, and so would have caught the attention of the Magi.

All this assumes that puzzle solvers are chasing a historical astronomical event. Many Bible scholars argue that Matthew's account of the Magi's travels – and the star guiding them – took place only in the author's imagination.

However you look at the Gospel account, the star's story no doubt has prodded more than a few people to scan the night sky during the holidays and marvel in its beauty and grandeur.

IN PICTURES: O Christmas Tree