Mashallah ibn Athari

In 762 CE the caliph al-Mansur wanted a new capital, and the choice of the day and hour to break ground was not left to convenience. A team of astrologers led by Naubakht the Persian was assembled to select an electional chart, a moment whose planetary positions were judged favorable for the city that would rise from it, and Masha'allah, a young Persian Jewish astrologer, was among them. The city they founded that day became Baghdad, and its rapid rise to become the intellectual capital of the early Abbasid world gave the astrologers who had chosen its hour a lasting institutional standing at court that Masha'allah held for decades, serving under al-Mansur and into the reign of al-Ma'mun.

His lasting influence, though, rests less on that single chart than on a theory he originated and later astrologers spent centuries elaborating: that Jupiter and Saturn, the two slowest visible planets, meet in conjunction roughly every twenty years, and that where and when these meetings fall carries information about the timing of major terrestrial change, dynasties rising and falling, and, in the hands of later writers, religions themselves appearing and fading. The theory's later, far more technical form is usually credited to Abu Ma'shar in the following century, but the founding claim, that the conjunction cycle tracks history, is Masha'allah's, and it was influential enough to reach medieval Latin Europe, where it shaped scholastic writers, and ultimately Johannes Kepler himself, eight centuries after Masha'allah first argued it.

Masha'allah wrote in Arabic, and most of his roughly twenty treatises survive only through later Latin or Hebrew translation, itself a sign of how far his reputation traveled beyond the Baghdad court where he began. Geoffrey Chaucer's own fourteenth century treatise on the astrolabe still drew, at several removes, on material tracing back to him.

Masha'allah's claim that Jupiter-Saturn conjunctions track history did not stay a general theory of dynasties for long. Medieval Jewish astrologers turned the same mechanism onto the history and future of the Jewish people specifically. Abraham bar Hiyya, a twelfth century Catalonian mathematician and astrologer, set out in his Megillat HaMegalleh a detailed reading of Jewish history keyed to these conjunctions, connecting Moses's birth, his flight from Egypt and his years in Midian each to a specific planetary conjunction, and holding as a general rule that a conjunction occurring in the sign of Pisces signaled some calamity for the Jewish people. Solomon Ibn Gabirol, the eleventh century poet and philosopher, shared bar Hiyya's further conviction that the same mechanism could be used to calculate the timing of the Messiah's arrival, treating the conjunction cycle as a kind of hidden clock running through scripture and history together.

Not every serious astrologer of the age accepted this. Abraham Ibn Ezra, the influential twelfth century scholar who did as much as anyone to bring astrology into mainstream medieval Jewish culture, and who elsewhere credited planetary conjunctions with marking the births of major prophetic figures including Moses, Jesus and Muhammad, explicitly rejected the specific attempt to calculate the Messiah's coming from a conjunction date. The disagreement matters for what it shows: this was not a fringe superstition indulged uncritically, but a live technical argument among astrologers who took the underlying mechanism seriously and still split over how far it could honestly be pushed.

Kepler later linked the 7 BCE Jupiter-Saturn conjunction in Pisces to the birth in Matthew's Gospel; the idea predates him and comes from this dispute.