Astronomy, Astrology, and the Star of Bethlehem
A story familiar to Christians is the Star of Bethlehem. The writer of Matthew tells of a star appearing over Bethlehem to signal the birth of Jesus. So significant was its appearance that wise men, called Magi, probably astrologers and possibly from the court of Persia or Babylon, traveled to Judea to find the newborn king that they believed the star heralded. Was it a really a new star or was it something else?
To determine astronomically what the star may have been we first need to set the date of its most likely occurrence. Biblical accounts presage the nativity with Mary and Joseph traveling to Bethlehem. John Mosley of the Griffith Observatory in California in his research on the star of Bethlehem describes a general taxation ordered by Caesar Augustus in 8 BC but believes that the correct translation refers to a registration or an oath of allegiance, in either 3 or 2 BC for Augustus' Silver Jubilee. Unlike a tax, an oath and registration might have required both Joseph and his wife to journey to Bethlehem. Either way these two interpretations bracket the birth of Christ between 8 and 2 BC.
Did any unusual astronomical phenomenon occur between 8 and 2 BC? As it happens there were several notable celestial events during that period. The Chinese reported two comets during that time. The comet of 5 BC, in Capricornus and visible for 70 days, was reported to have a tail. Professor Humphreys of Cambridge University believes that this comet, which he describes as having a vertical tail, appeared at the time of the Jewish Passover. Prof. Humphreys believes that this started the Magi, who were knowledgeable of the Jewish prophecy recorded in the Book of Micah, concerning the birth of a Jewish king, on their journey. If right about the vertical tail, this could agree with the biblical account in Matthew that the star "stood over where the young child was". The comet of 4 BC had no tail and whether it was actually a comet or a nova is unknown. While historians have usually suggested that comets were always bad omens, Humphreys believes that history shows them to be either good or bad omens.
If a comet or nova were not the star then could it have been a planet? In his account Matthew refers to the star in the singular, not the plural sense. At the time of the nativity Jupiter was in conjunction with Venus two times and with the bright star Regulus (named for royalty) three times in a ten month period during 3-2 BC. Could this have made Jupiter the "star" of interest? Or could the star have been more unique than Jupiter?
Uranus, which was at its zenith in 6 BC and in retrograde motion, would appear to be standing still overhead. With its magnitude varying between 5.7 and 6.1 it was just at the edge of naked eye visibility. Certainly only astrologers who study the sky intensely would have noticed a new "wanderer". Uranus would be a dim, hard to see object even at zenith and moving very slowly against the stellar background. This is not likely to be the sort of event that would send the court's philosophers on a long journey.
There is an astrological argument for a lunar occultation for the star of Bethlehem. Occultations had significant astrological import, a type of powerful conjunction, and both Jupiter and Saturn were occulted early in 6 BC. While occultations are common, the fact that they occurred in Aries, which was the house of Judea in Babylonian astrology, adds further weight as to their importance to the Magi. Researches believe that the astrologers of Babylon knew of occultations, as well as other alignments, even if they took place below the horizon or during daylight hours. This supports the idea that the star was not obvious but may have been known only to astrologers. Whether a comet, nova, or a planet any of these would classify the star as a singular event. However, this is not the complete story.
In the time frame under consideration there occurred two other celestial events of importance. First, in 7 BC, from May to December, a triple conjunction of the planets Jupiter and Saturn occurred in the constellation Pisces that was at that time the location of the vernal equinox. In astrology the vernal equinox meant rebirth and would be of great importance. According to the ancient prophecy of Judea and known to the Magi, this occurrence could mean that a king was to be born.
Three months later, in February of 6 BC a second remarkable event occurred. Mars joined Jupiter and Saturn for a massing of the planets in Pisces with the crescent moon added to the mix (see Figure on next page). Arranged in the western sky as if pointing over the horizon, this would have made a most impressive sight. During this massing were two occultations of Jupiter on March 20 and April 17 that were preceded by two occultations of Saturn the previous day. All occurred in Pisces as they approached Aries. Such a rare occurrence, once every couple of millennia, would have been unique in the cultural memory of the Magi. Additionally, the Magi believed Saturn was a father-god and Jupiter his son. This would have added some weight to the conjunction in Pisces, (vernal equinox and rebirth) just 3 months previously! Importantly, the two occultations of Saturn occurred during daylight or after it had set so only those who study the sky would have known it. Finally, the second occultation of Saturn occurred at the approximate azimuth of Bethlehem. This too, would have been known only to astrologers.
The importance of astrology in the story of the Star of Bethlehem should not be downplayed. The star was known only to the Magi and not witnessed by anyone else (Herod's "wise men" were not allowed to practice astrology) so it is unlikely that the star was a singularly bright star, comet or planet visible to everyone. Only those versed in both astrology and astronomy noticed its appearance.
The Sequence of Events
The following is a series of events that would have been significant to the Babylonian astrologers at the time of the nativity. The first was a triple conjunction in 7 BC between Jupiter and Saturn (father and son). Three months later, in 6 BC, a massing of Jupiter, Saturn, and Mars in Pisces near the vernal equinox (rebirth). Reinforcing the significance of this massing was the double lunar occultation of Jupiter and Saturn. Then two comets appeared. First a comet with a tail appeared in 5 BC followed by another comet (or a new star?) in 4 BC. Jupiter was in conjunction with Venus and Regulus (royalty) in 3 and 2 BC. Having been alerted by the first two events in 7 and 6 BC either comet of 5 or 4 BC or Jupiter's movements in 3 and 2 BC. could be the single "star" that Matthew referred to. These "multiple" events find further support in Matthew's account where he suggests that the Magi lost sight of the star but that it later reappeared. Notice too that the later the date the more closely it coincides with the oath and registration for Augustus in 3 or 2 BC.
What was most important to the Magi; the triple conjunction, the massing of the planets, the comets, a nova, four lunar conjunctions, Jupiter, or some combination of these celestial events, is not known to us. A sensible hypothesis is that some or all of these events, which occurred about the time of the nativity, were significant to the Magi, with their sequence and succession building in importance. This is perhaps the most reasonable scenario but at the same time it is certainly a very remarkable scenario, too.