The rendezvous of the Jupiter and Saturn was often grafted onto apocalyptic prophecies, says Rochester historian Laura Ackerman Smoller.
Astronomers and amateur star gazers alike are training their telescopes on the evening sky for a heavenly spectacle when听the conjunction of Jupiter听and Saturn is more visible from earth than it鈥檚 been in nearly 800 years.
The celestial event will play out on Monday鈥攖his year鈥檚 winter solstice鈥攚hen our solar system鈥檚 two largest planets appear above the horizon soon after sunset.
It鈥檚 been nearly eight centuries since the pair of planets appeared in conjunction this close to Earth. In 1623, a similar conjunction of the planets occurred, but on the same side of the sky as the sun, which meant it wasn鈥檛 visible from the Blue Planet. Monday鈥檚 conjunction will be the first visible occurrence since before the time of Marco Polo.
In the distant past, Europeans saw such alignments of the planets as signs of things to come, from famines, earthquakes, and floods, to the birth of Christ and the ultimate collapse of civilization.
鈥淥f course, predictions about individuals were dicier than large general predictions. That鈥檚 why, during the Middle Ages and the Renaissance, Saturn-Jupiter conjunctions were frequently grafted onto apocalyptic prophecies,鈥澨齭ays , a professor of history and chair of the at the 听

The author of (Princeton University Press, 1994), Smoller researches the intersection between magic, science, and religion in medieval and Renaissance Europe, centering around the two themes of astrology and apocalyptic prophecy, and saints and miracles. Her second book, 听(Cornell University Press, 2014),听delves into the canonization and cult of the Valencian friar Vincent Ferrer, a fiery apocalyptic preacher who died in 1419 and was canonized in 1455.听
For her current project, Smoller has returned to the stars鈥攕o to speak鈥攚here she鈥檚 tracing the interrelationship between astrology and prophecy for a third book, tentatively titled Astrology and the Sibyls鈥攁n investigation of ways of knowing the future ranging from around 1100 to around 1600.
Q&A with historian Laura Ackerman Smoller
Why the great medieval obsession with Saturn-Jupiter conjunctions?
Saturn and Jupiter were the two outermost planets in the Ptolemaic system; other planets had not yet been discovered.听They are also the two slowest moving ones.听According to doctrines that medieval European astrologers learned from Arabic astrologers, whose works鈥攖ranslated into Latin in the twelfth century鈥攆ormed the basis of medieval and Renaissance astrology, it鈥檚 when Saturn and Jupiter are found in the same area of the zodiac鈥攊n other words when they are in conjunction鈥攖hat there are profound effects on Earth.
What made these conjunctions so special?
The two planets come into conjunction approximately every 20 years.听Successive conjunctions form a roughly triangular pattern plotted against a diagram of the zodiac, meaning that three successive conjunctions will appear in the three zodiacal signs that form one of the trigons or triplicities鈥攖hat is, the fiery signs, watery signs, earthy signs, or airy signs.听Then, after approximately 12 conjunctions, the pattern will move into a new triplicity or trigon.听This shift鈥攚hich appears around every 240 years鈥攚as considered to be of great importance, bringing about changes in kingdoms, or in what medieval astrologers called 鈥渓aws and sects鈥濃攖hat is, religions.听After approximately 960 years, the pattern will return to the initial starting point in the zodiac, and this 鈥済reatest conjunction鈥 was said to have the most important effects of all.
Isn鈥檛 the belief in both astrology and Christian religion a contradiction in itself?
Astrology posed a fundamental dilemma for medieval Christians:听the notion that the heavens influenced the earth below was unquestioned (after all, one simply had to see how the moon affected the tides), but the stars鈥 control of earthly events seemed to threaten human free will.听If a person鈥檚 evil deeds were attributable to the stars, then how could God hold him or her accountable for sin? But medieval astrologers could also quote the Bible, saying 鈥淭he heavens proclaim the glory of God鈥濃擯salm 19:1) and saw the heavens as part of God鈥檚 Book of Nature, in which God had written signs of things to come. Astrology, medieval theologians and astrologers taught, was a science that God had revealed to the patriarchs.
Then how did theologians get around that conundrum?
That鈥檚 why predictions about general matters and about large crowds seemed safer.听Theologians like Thomas Aquinas acknowledged that the stars can influence the body but not the soul, and that most human beings are swept along by their bodily passions.听Hence, astrological predictions about large-scale events, such as wars, famines, changes in rulership, even large-scale religious changes were acceptable to medieval Christians.
In the late Middle Ages, even highly placed churchmen used these planetary conjunctions to predict the future of the Church. How so?
Pierre d鈥橝illy (1350-1420), a French cardinal who lived at the time of the Great Western Schism, when there were first two and then even three rival popes, worried like many contemporaries that the division in the church might signal the advent of Antichrist.听But he also hoped that a church council could solve the Schism.听In order to reassure himself鈥攁nd his contemporaries鈥攈e turned to astrology and to the doctrine of the great conjunctions.听To that end, D鈥橝illy plotted great conjunctions throughout history, noting that they presaged important religious and political changes.听For example, he pointed to a conjunction that predicted the birth of Christ and one that foretold the rise of Islam.听And he was convinced that a Saturn-Jupiter conjunction, along with other key astrological phenomena, would precede the arrival of the Antichrist鈥攚hich he predicted for the year 1789.
Sometimes historic events were even 鈥渇udged鈥 to make these predictions come true?
Saturn-Jupiter conjunctions became an absolute mainstay of astrological predictions in the later Middle Ages and Renaissance, in part because it took very little astronomical expertise to add groups of 20 years to a known 鈥渞oot鈥 conjunction.听One of the more famous of such conjunctions is that which occurred in 1484. After the fact it was said to have predicted the career of Martin Luther, a seminal figure in the Reformation, whose birth date was adjusted to conform to the conjunction year.听
Another example is the conjunction said to have predicted Noah鈥檚 Ark and the Flood. Although Pierre d鈥橝illy had originally posited that a greatest conjunction of Saturn and Jupiter had preceded the Flood by two years, he later had to acknowledge that most astrologers placed that conjunction at an awkward 279 years beforehand. On the bright side, however, his updated chronology allowed him to locate another greatest conjunction just five years and 320 days before the Nativity and Christ鈥檚 supposed birth.
Or, astrologers could always rely upon this handy piece of astrological doctrine: the less frequent the conjunction, the slower its effects would appear. That meant, in essence, that the effects of a 鈥済reatest conjunction鈥 had 960 years in which to unfold, so that, in d鈥橝illy鈥檚 estimation, a conjunction in 36 BCE signified the birth of Muhammad, more than five centuries later. All it took was a bit of historic leeway and date fudging.