Today, astrology is big business. In 2021, the global astrology market size was valued at $12.8 billion, and it is projected to grow to $22.8 billion by 2031. Yet despite its popularity, I don’t expect governments to start depicting astrological events on their coins and banknotes anytime soon. But around the time of Jesus’s birth, such depictions on the currency of the Roman Empire were commonplace. It is this historical fact that led the astronomer and ancient-coin collector Michael Molnar to speculate on what might have prompted the Magi mentioned in St Matthew’s Gospel to go on an expedition in search of a king.