One the questions often posed to and by astronomers this time of year is “What was the Star of Bethlehem?” Was the Star of Bethlehem a real astronomical event? Was it a myth created by the early church? Or could it have been something else?
The Star of Bethlehem is a star in Christian tradition that revealed the birth of Jesus to the Magi or wise men and led them to Bethlehem. According to the Gospel of Matthew, the only place in the New Testament mentioning the Star, the Magi were men from the east who were inspired by the appearance of the Star to travel to Jerusalem to search for the “King of the Jews”. In Jerusalem the Magi met King Herod, who informed them that the child that they were searching for was in Bethlehem. The Magi traveled to Bethlehem, found Jesus and his parents, paid homage to him, presented him with gifts and then returned to the lands from which they came.
Because the magi told Herod that they saw the star “at its rising”, it is easy to assume that the Star of Bethlehem is an astronomical object. If the Star of Bethlehem was an astronomical event, it must have been a comet, a nova, a supernova, or a planetary conjunction. To ascertain what astronomical event corresponds to the Star of Bethlehem was, we first need to attempt to determine the date of Jesus’ birth.
Determining the Date of Jesus’ Birth
While there is no historical accounting of the birth of Jesus, we know, from biblical references, that Jesus was born while Herod was King. Herod reigned between 37 and 4 B.C.E. We also know from biblical accounts that the wise men came to pay respects to the child Jesus,not the newborn Jesus. This conclusion was reached based upon King Herod’s orders to kill every child in and around Bethlehem who were two years old or younger. 
Jesus was “about” thirty when he began his ministry, and the books of Matthew, Mark, Luke, John, and Acts of the Apostles, the Jewish author Josephus and the Roman author Tacitus all state that Jesus was killed during the rule of Pontius Pilate, the governor of Judea, C.E. 26 through 36.  Also, John the Baptist and Jesus began their ministries around the same time, that is in the fifteenth year of the reign of Emperor Tiberius (C.E. 14-37), when Pontius Pilate was governor of Judea (C.E. 26-36), Herod Antipas was tetarch of Galilee and Perea (4 B.C.E.-C.E. 39), Herod Philip was tetarch of Batanea, Trachonitis, and Auranitis (4 B.C.E.-C.E. 34), and Caiaphas was high priest (C.E. 18-36). This places the date between C.E. 27 and 29.
So, if Jesus was about thirty in the years C.E. 27 through 29, and was born while Herod was King, and was at least two before Herod’s death in 4 B.C.E., then Jesus was born somewhere between 7 and 5 B.C.E..
We seem to have narrowed down Jesus’ birth year to somewhere between 5 and 7 B.C.E. Since the Magi visited the child Jesus and King Herod ordered the deaths of all children 2 years and younger, the Magi visit occurred between 4 and 5 B.C.E.
Can we determine at what time of the year Jesus was born? Let’s take a look at the Book of Luke again. Luke records that shepherds were watching over their flocks by night. There are only two specific times in a year when this was done, namely when lambs were being born in the spring or autumn. At other times of the year they were kept safely in their sheep-folds to protect them from wild animals. So Christmas may be celebrated eight months too late. Without historical documentation it may ultimately be impossible to know the day and month of Jesus’ birth.
These estimates are as close as we can get, without an historically documented event.
Finding an Astronomical Event
The sole unusual event surrounding Jesus’ birth that is mentioned in the Bible is the Star of Bethlehem, so we look to the skies.
What astronomical events occurred in those three years? In 7 B.C.E. there was a triple conjunction of Jupiter and Saturn in Pisces, one in late May, one in late September, and one in early December. A conjunction is when two or more objects appear very close together on the sky. Pisces is associated with the Jewish people in astrology, so when Jupiter and Saturn passed very close to each other three times during the span of several months in 7 B.C.E. it was a notable event. Adding to the significance of this conjunction is that this triple conjunction in Pisces occurs once every 900 years.
In February, 6 B.C.E., Jupiter, Saturn, and Mars passed within 8° of each other in the constellation Pisces. This near conjunction occurs only once every 800 years. Jupiter was the “star” of royalty and luck. Saturn was the “star” of the Mesopotamian deity who protected Israel. These conjunctions would have been easily predicted by astronomers/astrologers of the time and most likely interpreted as a great king was to be born in Israel.
In March/April of 5 B.C.E. Chinese astronomers recorded a “new” star in the constellation of Capricorn which was visible for over 70 days. The “new” star could have been a nova or a supernova. A nova is caused by a white dwarf gathering enough material, usually from a nearby companion in a binary system, onto its surface to raise the surface pressure high enough for a thermonuclear explosion. The white dwarf’s increase in brightness may be a factor of 10,000 to over one million. The increase to peak brightness is very rapid, within a few days, while the fading away to invisibility usually takes a few months. A supernova is caused when a star at least 8 times as massive as our Sun reaches the end of its life and suddenly explodes and throws off most of its mass. For a few days a supernova may outshine its host galaxy and will slowly fade away. This “new” star would have been visible in the east, several hours before sunrise.
In May of 5 B.C.E. Jupiter emerged from behind the Sun and passed through a stationary point in September. Jupiter appears stationary for about a week at the beginning and end of a retrograde motion cycle. Could this have been the Christmas Star? Unlikely, the magi were astrologers and would have recognized these events for what they were.
Could the “new” star in March/April of 5 B.C.E. have been a comet? Probably not. The Chinese called comets “broom stars” because of their tails. Although the “new” star could have been a comet with a tail too faint to detect without optical aid, the Chinese astronomers did not report any movement of the “new” star; and as we all know, comets move across the sky. Halley’s comet made an appearance in 12 B.C.E., but that is outside the probable date range for the birth of Christ.
None of these events seems to fit the Star of Bethlehem very well. But if the assumption is made that the Magi visit occurred when Jesus was between 18 and 24 months old. And that this visit was triggered by a celestial event. The conjunctions of 7 B.C.E. are out of the range of probable dates of the Magi visit. As is the conjunction of 6 B.C.E. It is unlikely that the motions of Jupiter in 5 B.C.E. would have caused astrologers to begin a journey to Bethlehem. This leaves the new star of March and April 5 B.C.E. As the “best fit” to be the “Star of Wonder”.
As to other sources of the Star of Bethlehem, I will leave that to others to ponder. The Star is what it is: a symbol of hope to over a billion people.
- Matthew 2:11
- Matthew 2:1-2
- Matthew 2:11-12
- Matthew 2:2
- Matthew 2:7-10
- Matthew 2:12-16
- Luke 3:23
- Joseph ben Matthias (Flavius Josephus) 70, The Jewish War
- Joseph ben Matthias (Flavius Josephus) 93, Jewish Antiquities
- Tacitus 81, Annals
- Luke 3:1-2
- Luke 2:8-9
- Bulmer-Thomas, Ivor 1992, Quarterly Journal of the Royal Astronomical Society, vol. 33, p. 363.
- Kidger, Mark, “Chinese and Babylonian Observations”