Star or comet?

For centuries, scholars have been captivated by the mention in the Gospel of Matthew of wise men from the East who, following a star, came to worship Jesus. What did the wise men see? What prompted them to set out? If this turned out to be some unusual astronomical phenomenon, by determining when it was visible, we might be close to knowing the true date of Christ's birth.

The most popular hypothesis was that the mysterious phenomenon was a comet. Halley's Comet, which appears in the sky every 76 years, was suspected. However, it passed in 12 BC, which was too early. This hypothesis has another serious weakness. "A comet was usually considered a bad omen, a symbol of impending misfortune, yet the sages interpreted it completely differently," explains Dr. Jarosław Włodarczyk from the Institute of the History of Science of the Polish Academy of Sciences.

Then came the idea that the mysterious phenomenon was a supernova, a gigantic stellar explosion that could be visible for a very long time. This would be an interesting hypothesis, except that the astronomers of the time who knew and described these phenomena failed to observe such an explosion between 135 BC and 173 AD.

The most widely supported hypothesis is that of the eminent astronomer from Gdańsk, Johannes Kepler (1571–1630). Based on medieval chronicles, he discovered that the so-called conjunction of Jupiter and Saturn occurred in 7 BC. A conjunction means a union, in this case an apparent one. The three planets align with the Earth in relation to the Sun, so that they appear as if they were one large, bright star. In 7 BC, Jupiter and Saturn conjunct three times.

"This hypothesis has one weakness. According to the principles of astrology of the time, the conjunction of Jupiter and Saturn meant nothing that could have led the sages to conclude that a king had been born in Judea," argues Jarosław Włodarczyk.