to inspire Hipparchus’s invention of trigonometry too. Hipparchus’s reliance on Babylonian astronomy is so extensive, in fact, some scholars think he must have visited the Esagila temple himself and worked with the priests there, copying observations and equations from their tablets and converting them into Greek. More than that, contact with the priests may have transformed his very approach. After the hand-waving philosophical discussions back home, Hipparchus must have been ‘shocked’, says Evans, to discover that the Babylonians were accurately predicting future positions of the sun, moon and planets in the sky. No wonder he made it his mission to make the Greek models just as precise.
In Hipparchus, then, two opposing worldviews collided. The Babylonian arithmetic progressions yielded precise predictions but included no three-dimensional structure, while the Greeks had geometric models but no accurate numbers. Neither approach on its own could produce a complete description of the sky. When they came together, the science of astronomy was born.
Of course, that wasn’t all the Babylonians helped to forge. Entwined with astronomy from the beginning was the parallel discipline of astrology.
•
In September 1967, French archaeologists excavating near a Roman sanctuary at Grand in northeast France found broken fragments of ivory at the bottom of an ancient well. Along with pottery, jewellery, fruit stones and shoes, the team eventually recovered nearly 200 pieces from two pairs of ivory tablets, smashed and discarded around AD 170. Their surfaces still hold traces of gold leaf and coloured paint, and they’re beautifully carved with a circle of figures still intimately familiar today, from a crab and scorpion to two scaly fish. They were used for casting horoscopes.
Before Alexander conquered Babylon, the Greeks had plenty of ways to foretell the future, from dream specialists to temple oracles, but there was no particular tradition of reading someone’s fate in the sky. Without the ability to calculate the positions of the sun, moon and stars, the idea of casting a horoscope simply didn’t exist. But some time in the second century BC, after contact with Babylon, a craze for astrology swept through the Greek and Roman world. It reached throughout the Roman Empire but was particularly popular in Greco-Roman Egypt. Elaborate zodiacs start appearing on Egyptian temple ceilings, and papyrus fragments found in ancient rubbish dumps have yielded hundreds of briefly scrawled horoscopes, noting details of the sky at the moment of a person’s birth. James Evans suggests these were astrologers’ notes, summarising information about a client that would be displayed during a consultation on a board like the tablets from Grand. These have portraits of the sun and moon carved in the centre, surrounded by a zodiac circle. Around that are thirty-six decans, groups of stars that the ancient Egyptians used to divide up the sky.
A narrative poem called the Alexander Romance (a fictional version of Alexander the Great’s life, which exists in several versions and originates from the second century AD) includes a passage describing how a similar tablet was used. In the story, the last native Egyptian pharaoh, Nectanebo II, travels to the Macedonian court after being defeated by the Persians, posing as an astrologer as part of an elaborate plan to trick Queen Olympias – who would later give birth to Alexander – into sleeping with him. He tells the queen that the horoscope reveals a ram-horned god will visit her during the night; Nectanebo subsequently disguises himself as this deity. During the consultation, Nectanebo uses a ‘princely and costly board’ made of ivory, ebony, gold and silver, decorated just like the Grand tablets. He opens a small ivory case and carefully pours out gemstones to represent the celestial bodies – crystal for the sun, sapphire for Venus, a blood-red stone for Mars – placing them on the board to show their positions in the heavens at the moment of the queen’s birth. In Greco-Roman times, wealthy clients probably had such consultations in temples and sanctuaries, says Evans. For everyone else, street astrologers may have cast horoscopes in squares and markets, drawing their charts in sand trays or on the ground.
The inspiration for astrology based on birth charts and zodiac signs – the kind we recognise today, popular in New Age websites and self-help books – is often credited to the ancient Egyptians; classical writers say it was invented by a seventh-century pharaoh called Nechepso. Greek astrology did incorporate traditional Egyptian elements – not least groups of stars called decans, originally used to tell time at night – and added features such as the ‘horoscopic point’, the part of the ecliptic rising at the time of birth after which the entire chart was named. But as with mathematical astronomy, the fundamental ingredients of western astrology come from Marduk’s priests.
Since around 400 BC, the Babylonian scribes had been branching out. Instead of just giving predictions for king and country, they made forecasts for individuals based on the position of celestial bodies in the sky at the time of birth. Epping and Kugler deciphered the first Babylonian ‘horoscopes’; a few dozen are now known. One of the earliest, dating from 410 BC, records the birth of a child on the fourteenth night of the month Nisannu, when Jupiter was in Pisces, Venus in Taurus, and the moon was beneath the ‘Horn’ of the Scorpion (the stars of our constellation Libra). ‘Things will be good for you,’ the tablet says.
While the Babylonians’ astronomical techniques enabled Greek astrology, the desire to study horoscopes was in turn a key motivation for Greek astronomers. Hipparchus wrote a now-lost treatise on astrology, with the historian Pliny the Elder remarking that he ‘can never be sufficiently praised, no one having done more to prove that man is related to the stars and that our souls are a part of heaven’. Ptolemy was also an advocate. Alongside the Almagest, he wrote another epic and hugely influential work, Tetrabiblos, in which he summarised the methods of astrology and tried to arrange them in a logical system. Personal qualities ‘which concern the reason and the mind are apprehended by means of the condition of Mercury’, he wrote, ‘and the qualities of the sensory and irrational part are discovered from . . . the moon.’ Ptolemy’s approach differed from the Babylonians in that rather than seeing celestial signs as divine warnings, he believed powers emanating from stars and planets, such as ‘humoral shifts’, could trigger effects on Earth, influencing everything from the weather to personality and health. But he too was driven to achieve mathematical accuracy at least partly because he wanted to read human secrets in the stars.
It took more than a thousand years before scholars in western Europe superseded Ptolemy’s system and constructed our modern, heliocentric view of the heavens. In 1543, Copernicus suggested that the sun, not the Earth, is at the centre of the cosmos, a theory supported by Galileo when he turned his telescope skywards and found, for example, that Venus has phases like the moon. Then, in 1609, Johannes Kepler banished epicycles and equants when he realised that celestial orbits are not circular but elliptical.
For these founding fathers of astronomy, the idea that the stars influence our fate was still embedded in their motivation and world-view. Galileo regularly made astrological predictions for rich clients, and drew up horoscopes for his illegitimate daughters. Kepler hoped to strengthen and reform the discipline, describing himself as ‘throwing out the chaff and keeping the grain’. He discounted the idea that cultural inventions like names or zodiac signs could affect earthly events. But he firmly believed that different qualities of light from the various planets could influence climate and health, and he suggested that just like human beings, the Earth has a soul, sensitive to the harmonies of the stars.
Ultimately, though, astrology was incompatible with the scientific revolution. In 1641, the French philosopher René Descartes famously separated mind from body, consciousness from the material world – part of an inexorable shift in the West towards physical causation as the only acceptable type of explanation. Astronomy and astrology had to go their separate ways: the former making sense of the universe based on objective measurements; the latter emphasising intangible connections and subjective meaning. There could only be one winner. Without an obvious physical mechanism by which distant celestial bodies might affect our lives, the intellectual standing of astrology slowly collapsed.
While scientific astronomy soared, astrology was left to ‘stumble along’,
