The history of astronomy is intertwined with that of astrology, and an understanding of the history of astronomy necessitates familiarity with the role that astrology played in ancient times: even as recently as the era of Kepler, the preparation of astrological almanacs was commonly part of the job description of astronomers.  In this article Ian Bacon outlines the known history of astrology in the classical world of ancient Greece and Rome.

Ian Bacon is an enthusiastic amateur astronomer in the city of Perth, Western Australia. His principal interests are deep sky objects (galaxies, clusters and the like). He also takes part in asteroid occultations, occultations and is still seeking the elusive Leonid Meteor Shower.  Professionally Ian works as a computer programmer. His interest in historical astronomy has led him to undertake first a Masters and now a Phd in classical astronomy and astrology.

If you have any questions about this Guest Contribution, don't contact Ian directly please.  Instead, post them to the Astronomy News forum and we'll put them together & forward them to Ian for comment.
 

A tendency in the modern world is to view astrology as an inferior by-product of the science of astronomy. In the ancient world of the Greeks and the Romans, where the supernatural still played a large role, this was not the case.

Astrology in the western tradition began principally in Mesopotamia, modern Iraq. It is associated with the great city of Babylon, so much so that astrologers came to be known as 'Chaldeans' - the priestly class of Babylon. Ancient Egypt supplied relatively little astrological lore since neither astronomy nor astrology were practiced to any great extent there.

The earliest recorded usage of astrology is around 1000 BC as part of a uncomplicated 'omen' divination system where various terrestrial, meteorological and astrological phenomena were combined to foretell the future. Babylonian astrology was originally a 'judicial' (state based) system which was used to foretell events that would affect the nation and the king; ordinary individuals played little part. A seventh century BC sky-omen states that:  "On the 1st of the month of Nisan ... there will be a solar eclipse ... the King will die that very month and his son will ascend the throne."

The Greek world came into widespread contact with middle-eastern astrology with Alexander the Great's conquest of the Persian empire (334-323 BC). The first major astrological prediction of the Greek world was a claim that Alexander would die in Babylon. He attempted to evade this prophecy but it proved to be all too true. Prior to this, in the early stages of Greek civilisation (contemporary with Plato, Aristotle and Eudoxus), the Greeks had little conception of astrology. They did, however, regard events in the sky as influential. In 413 BC the Athenian general Nikias was unsettled by a lunar eclipse and consequently acted unwisely and suffered military defeat.

In the centuries after Alexander (the Hellenistic period), astrology became widespread throughout the Greek world. Alexander's empire was split after his death and the rulers who succeeded him had astrologers at court to advise and warn them. This growth in astrology was fostered by a new Greek philosophy, Stoicism, which originated with a Greek named Zeno around 300 BC in the city of Athens. Stoics believed in fate and that the entire universe was an aspect of the mind of God. The stars were understood to foretell the future via 'cosmic sympathy'.

By the last centuries BC, astrology had developed into a distinct art form. It was based upon the findings of Greek astronomy and possessed a mathematical basis borrowed from Greek science. The orientation of astrology also changed into that of personal predictions. This form of astrology is known as 'genethlialogy'. The procedure used to foretell this personal future was the casting of a horoscope. This is essentially a 'snapshot' of the relative positions of the Sun, Moon, planets and the zodiac (discovered in the fifth century BC) at the time of birth or conception. By interpreting the relationships of these objects an astrologer could claim to predict the subject's future. There were many different 'schools' of astrology, each with their own formulae, technique and results.

By the second century BC the increasingly powerful Roman Republic came into close cultural contact with Greece. New ideas flowed into Rome; some were unsuccessfully resented by conservative elements. One such new idea was astrology. While Roman society had a practical orientation (e.g. engineering) it was also highly superstitious and seized upon astrology. During the first century BC, amidst the turmoil and violence of the collapse of the Republic, most prominent Romans relied on astrologers for counsel. However, one prominent Roman statesman of the time, Cicero, questioned the validity of astrology by asking why twins born at the same time did not experience the same fate?

The belief in astrology flowed into the Roman Empire which succeeded the Republic. The Roman emperors used astrology as one means of justifying their rule. The first emperor Augustus used his sign (Capricorn) on his coins and claimed that his elevation was foretold by his horoscope. This reliance proved to be a double-edged sword. Astrology could also predict an emperor's death and the identity of his successor. In AD 11 (in his 74th year) Augustus restricted the casting of horoscopes and even expelled astrologers from Rome, to no avail. His successor Tiberius went one step further. Roman historians suggest that he had his court astrologer Thrasyllus cast the horoscopes of important men. If any had the potential to supplant him they were executed. A later emperor, Septimius Severus, had his horoscope recorded on the ceiling of his palace, but with the critical details blank so that his own death could not be foretold.

Astrology remained important in the Roman world until the collapse of the western empire in the fifth century AD. In the Christian Dark Ages of western Europe, astrology was disapproved of and partly forgotten.

Further Reading:
The principal ancient astrological texts that survive to the current day are the Astronomica by Marcus Manilius and the Tetrabiblos by Ptolemy Claudius.
For modern historical analysis of ancient astrology see Ancient Astrology by T Barton and Origins of Astrology by Jack Lindsay.
 

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