Is astrology nonsense? Was Ptolemy a fool? Whatever you think, there’s no denying its influence of Western culture. Seb Falk looks at its rich history

“Don’t second guess yourself. Tie a piece of green thread around an object that reminds you of winter. Meditate in front of it for nine minutes and think about spring.” That is today’s advice from Astro Poets (695.5K Twitter followers) for anyone who’s an Aries.

Written off as new-age woo in the 1970s, when its popularity last peaked, astrology has come roaring back for another generation. Millennial astrologers broadcast horoscopes on Instagram and deliver personalised advice via apps like Co-Star. If you prefer a Zoom consultation, the UK’s Faculty of Astrological Studies, “Raising the Standard of Astrology since 1948”, recommends a list of accredited practitioners. “Fees vary according to the amount and type of work required”, but £150 for a 90-minute consultation is typical.

You may think all this is ridiculous. (If so, there’s a feed for you too: Sorrowscopes, the relentlessly downbeat parody of astrologers’ pithy wisdom, where this week Arians are advised to “Stop wasting precious time and energy hating yourself; let others do it for you.”) Either way, I’m certain you know whether this advice is directed at you: you know whether you’re an Aries, or one of the other 11 zodiac signs whose names are indelibly inked into Western culture.

This isn’t the first time astrology has boomed – and been ridiculed. Back in second-century Alexandria, the great astronomer Ptolemy admitted that astrology’s critics dismissed it as “incomprehensible” and “useless”. Its difficulty, he said, should not poison its potential to offer valuable knowledge. Nor should its worth be undermined by the inflated claims made by some fraudsters, who promise gullible clients knowledge of the future, or pass off silly numerology as a science. The power of the planets was obvious – any farmer or sailor had some empirical knowledge of seasons and winds. But precise prediction, he argued, took real effort and skill.

In some ways Ptolemy’s science of the stars was very different from today’s Instastrologists. Ancient and medieval astrology was a physical discipline, focused on the interactions of elements in the atmosphere and down here on earth. It was based on the principle that all matter was connected. If the sun heats the earth, and the moon controls the tides, it made sense that the other planets, slowly orbiting against the background of stars, could have their own effects. Just as the sun was hot and dry like fire, and the moon cold and wet like water, each planet had a pair of qualities, matching one of the four classical elements.

Those elements, in turn, mapped onto the four humours of ancient medical theory. So airy Jupiter, warm and wet, shared qualities with blood, and might be associated with blood-related illnesses. These associations linger in the words we use for personalities once associated with Jupiter: “sanguine” or “jovial”.

A skilled astrologer, then, could not only predict the weather but also diagnose and treat disease. It was generally accepted, for example, that each of the 12 zodiac signs governed a part of the body, from Aries at your head to Pisces at your feet. At all costs, a physician should avoid treating a given organ when the moon was moving through its corresponding sign.

As medicine became a regulated professional discipline in the later Middle Ages, city authorities demanded that doctors carry almanacs, in order to find the moon’s sign on any given day. They were also advised to have an astrolabe: a flat brass disc with moving parts that modelled the motions of the heavens, allowing astrologers to shortcut fiendishly complex calculations. Astrolabes became an iconic part of medieval culture, immortalised in art and literature; even Chaucer wrote an astrolabe manual, the very first in English (as well as weaving astrological references through The Canterbury Tales). In turn, these multifunctional devices had an enormous influence on the development of later scientific instruments. Clocks run clockwise because that’s how astrolabes worked, while the sextants used by every mariner to find their location before the invention of GPS were based on the altitude-measuring function of an astrolabe.

While modern astrologers give little thought to the elements, rarely predict the weather or offer medical prognoses to patients, astrological theory has remained remarkably consistent. It’s still based on the motions of the planets against the fixed background of stars, and the characteristics attributed to each – Jupiter as a planet of wealth and success, for example. The sky is still divided in the same way: not only into the 12 zodiac signs that are the same everywhere, but into 12 “houses” that are specific to the observer’s location: there are always six houses above your local horizon, three on either side of the meridian. Again, the characteristics of those houses have not changed since Ptolemy’s day. For instance, the first house or “ascendant”, just coming up above the horizon, is the all-important place of beginnings and questions (and since every horoscope is a sort of question, one should never neglect the ascendant).

Over the centuries, horoscopes have been cast to answer every question imaginable: from finding a thief to predicting the sex of a child. The Abbasid caliph al-Mansur consulted two astrologers, one Muslim and one Jewish, before deciding on the afternoon of 30 July 762 for the foundation of his new capital. (Baghdad quickly became the largest city on earth: coincidence?) More recently Ronald Reagan took astrological advice before making every important decision during his presidency. In 1441 two Oxford scholars who had cast a horoscope predicting the imminent death of Henry VI were accused of planning to assassinate the king, tried for treason and executed. Henry himself then commissioned an alternative horoscope showing he would live to a ripe old age.

Such alternative horoscopes were possible because of the infinite complexity of the discipline. It was a constant struggle to track the stars as they moved in relation to each other and to us. Indeed, astrology’s pursuit of ever-more precise planetary data drove the development of astronomy, the first truly mathematical science. The stunningly accurate geometrical models Ptolemy developed to predict the motions of the sun, moon and planets were unsurpassed for 1,500 years. When Ptolemy’s geocentric system was finally, gradually, overturned in the 16th and 17th centuries, it was by astronomers – Copernicus, Tycho and Kepler – who were steeped in astrology, and whose more accurate astronomical tables were of primary interest to practising astrologers.

Yet the mass of data required for astrology raised questions about its validity. The most common kind of prognostication was a nativity: a snapshot of the heavens at the moment of a client’s birth. Pre-modern astrologers didn’t just look at where the sun was among the stars – the origin of our “star sign” today – but would measure the angles between the planets, and locate each in a house. However, all of that information could change extremely rapidly, as the stars rotate above our heads once a day. A planet can quickly move from the ascendant, the house of beginnings, into the 12th house, the place of enemies and misfortunes.

Medieval astronomers noted this and wondered if planetary influences could ever be accurately predicted. Although the Middle Ages are often scorned as a time of credulity and conformity, there was intense debate on every topic imaginable. Some philosophers questioned how astrology could predict different fates for conjoined twins, born at precisely the same time and place. Others worried about its determinism, and the impact on our God-given free will. (Physicists continue to argue about that today, albeit in modern terms.) One scholar named Heinrich Selder called astrology the devil’s work, a stain on genuine mathematical astronomy. “Among all the harlots of divination,” he thundered, “none imitates the honest face of a chaste and venerable matron as much as this one.” To prove just how bogus it was, he arranged to have blood taken from his arm when the moon was in Gemini, against all medical orthodoxy. “I did not feel anything bad,” he reported.

Countless experiments since Selder’s time have failed to find any evidence to support astrology. Yet it persists. It’s embedded in our language and culture: the days of the week – with Sunday following Satur(ns)day and mardi preceding mercredi – come from the doctrine of planetary hours, an ancient system in which one of the seven classical planets is given rulership over each day. Many people continue to read their horoscope, even if they don’t actually change their behaviour. In the same way, Chaucer wrote that “my spirit hath no feith” in astrological decision-making – but he supplied instructions for finding the ascendant anyway.

The 12-paragraph newspaper horoscope, with humanity divided neatly into a dozen groups purely according to our sun sign, was an innovation of the 20th century. The key to its modern success was its abandonment of physical, material prediction: the astrologers of the 1930s who developed it focused entirely on people’s states of mind. That suited a period when science promised to explain everything in nature, leaving no room for religion or other worldviews. Many people instinctively felt, like Hamlet in a play full of astral allusions, that there were “more things in heaven and earth” than could be explained.

Today we’re used to hearing about algorithms that can predict our behaviour so accurately that they seem to know us better than we know ourselves. Astrology, too, satisfies our desire for explanations. (And humans, instinctive pattern-spotters, will always notice the chance successes and forget the erroneous predictions.) Like such fads as Learning Styles and Myers-Briggs personality types, once popular with teachers and employers but now largely debunked, astrology promises to make sense of our unpredictable thoughts and feelings.

In an age when we’re often told that the answers are within ourselves, it doesn’t deprive us of our free will, but gives us excuses for our behaviour. The stars follow cycles, every configuration has a precedent, so perhaps “everything happens for a reason”. And grouping ourselves into 12 tribes satisfies our basic urge to belong. No surprise, then, that among the most recent developments are a plethora of astrological dating apps. As the founder of the most successful one, The Pattern, says, “people are hungry for depth and something a little more.” Weren’t we always?

Seb Falk teaches history at the University of Cambridge, and is a BBC New Generation Thinker. His first book, The Light Ages: A Medieval Journey of Discovery, was a Book of the Year 2020 in The Times, The Telegraph, The TLS and BBC History magazine.

This article is from Idler #86.

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