Friday, July 16, 2010

Ptolemy's mistake (and the origin of Western astrology)

The name of Ptolemy, the astronomer, cartographer and astrologer, has become almost legendary as representing a multifaceted scholar during the declining phase of the Hellenic world. This impression may be largely undeserved. In fact, the writings and many errors made by Ptolemy suggest he was not the expert his books made him out to be. Importantly, he adopted an astronomical calculation concerning the starting point of the zodiac which resulted in a fictitious moving (tropical) zodiac being populalrised. This was undoubtedly based on a misunderstanding and his advocacy of this calculation in his book resurfaced in Europe during the Renaissance in the late Middle Ages and became the basis of the birth of modern Western astrology.

Claudius Ptolemaeus
Claudius Ptolemaeus (c. AD 90 – c. 168), known in English as Ptolemy, was a Roman citizen of Egypt who wrote in Greek. He was a mathematician, astronomer, geographer, astrologer and a poet of a single epigram in the Greek Anthology. He lived in Egypt under Roman rule and died in Alexandria around AD 168. Ptolemy was the author of several treatises, at least three of which were of continuing importance to later Islamic and European science. The first is the astronomical treatise known as the Almagest ("The Great Treatise“). The second is the Geography, which is a thorough discussion of the geographic knowledge of the Greco-Roman world. The third is the astrological treatise known as the Tetrabiblos ("Four books"), in which he attempted to adapt horoscopic astrology to the Aristotelian natural philosophy of his day.[1]

Errors in calculations
While evidently accomplished as a writer and celebrated during the middle ages, the originality of his works has been cast in doubt due to his unfamiliarity with the astrological practices of his time and the many important errors made in his books. His importance is not least traced to his major work, the Almagest, which is the only surviving comprehensive ancient treatise on astronomy in the Hellenic world. Indian and Babylonian astronomers had developed arithmetical techniques for calculating astronomical phenomena; Greek astronomers such as Hipparchus had produced geometric models for calculating celestial motions. Ptolemy, however, claimed to have derived his geometrical models from selected astronomical observations by his predecessors spanning more than 800 years, though astronomers have for centuries suspected that his models' parameters were adopted independently of observations. Ptolemy presented his astronomical models in convenient tables, which could be used to compute the future or past position of the planets. Later, it was demonstrated that his ephemeris is of dubious quality, diverging significantly from the calculations of his contemporaries. Because Ptolemy derived many of his key latitudes from crude longest day values, his latitudes are erroneous on average by roughly a degree (2 degrees for Byzantium, 4 degrees for Carthage), though capable ancient astronomers knew their latitudes to more like a minute. He agreed that longitude was best determined by simultaneous observation of lunar eclipses, yet he was so out of touch with the scientists of his day that he knew of no such data more recent than 500 years ago (Arbela eclipse). In terms of cartography, when switching from 700 stadia per degree to 500, he expanded longitude differences between cities accordingly (a point first realized by P.Gosselin in 1790), resulting in serious over-stretching of the Earth's east-west scale in degrees, though not distance.

Ptolemy‘s popularity was based on his Handy Tables, a useful tool for astronomical calculations and a model for later astronomical tables. In the tables was tabulated all the data needed to compute the positions of the Sun, Moon and planets, the rising and setting of the stars, and eclipses of the Sun and Moon – albeit with a large margin of error. Ptolemy‘s Planetary Hypotheses went beyond the mathematical model of the Almagest to present a physical realization of the universe as a set of nested spheres, in which he used the epicycles of his planetary model to compute the dimensions of the universe. He estimated the Sun was at an average distance of 1210 Earth radii, which is one twentieth of the actual distance. Meanwhile, he calculated the radius of the sphere of the fixed stars as being 20,000 times the radius of the Earth, or within the distance of the Sun. It is uncertain if other astronomers of his day were so widely off in their distance calculations.

Certainly, his most crucial error was in failing to correct for the precession of the equinoxes in order to anchor the zodiac and the fixed planets which make up the constellations in the sky. Rather, he and some other Roman astrologers, chose not to make this correction. At that time, the difference between the classical sidereal zodiac was only a few degrees. However, by the time astrology was rediscovered in the West, almost a millennium later, the difference had grown in size by over 10° and at the present time it is 24°. In some few hundred years, the signs in the tropical zodiac will be one whole sign removed from their original counterparts in the sidereal zodiac. Clearly, those failing to make this adjustment did not anticipate that development.

A narrow view of Astrology
Ptolemy's treatise on astrology, "Tetrabiblios" (Greek tetra means "four", biblos is "book"), was the most popular astrological work of the middle ages and had great influence in the Islamic world and the medieval Latin West. It was translated from Arabic into Latin by Plato of Tivoli. However, its later popularity also reflects the dearth of written sources on this knowledge at the time. The Tetrabiblos is an extensive and continually reprinted treatise on some principles of astrology that Ptolemy felt were important. That it did not quite attain the unrivaled status of the Almagest was likely because it did not contain a very rigourous treatment of the subject matter in terms of horoscopic astrology proper, thus eluding a comprehensive approach.

The great popularity that the Tetrabiblos did possess might be attributed to its nature as an exposition of the art of astrology and as a compendium of astrological lore, rather than as a manual. It speaks in general terms and avoids illustrations and details of practice. Much of the content of the Tetrabiblos was collected from earlier sources; Ptolemy's achievement was to order his material in a systematic way, showing how the subject could, in his view, be rationalized. At the same time, it reveals that Ptolemy was not an expert on the subject. Ptolemy was concerned with the influences of the celestial bodies which he believed travelled in the sublunar sphere, with a focus on planetary attributes in terms of their heating, cooling, moistening, and drying influences. In short, the astrology he described was a very limited expression of the horoscopic astrology of the day, as documented for instance in the contemporary Yavanajataka, the astrology of the Yavanas (Greek speaking people of the Indo-Greek world). This only points to the fact that Ptolemy did not truly understand the import of his woeful recommendation to calculate the zodiac without a precession correction.

Greek and Roman world
The introduction of the ancient astrology of India into the religious and philosophical milieu of the Hellenic and Roman world are also of interest. The mentaility of this time and location was different from the more ancient vedic civilisation. The nascent Western civilisation was more materialistic and positive in approach but also politheistic. While the Greek people saw the Olympic gods as supermen, rather than an all pervading single deity, the thinkers and heterodox religious leaders of the day debated various philosophical points including the role of gnosticism in religion. Already in the time of the Hellenic world, the ideological soil had become inhospitable to the original horoscopic astrology of Jyotish, as the sixth branch of the vedic science of enlightenment. Moreover, as the Western civilisation moved westward to the Roman empire, the distance between the source of this wisdom in India and its Western practitioners increased. As a result, even the horoscopic astrology began to change in terms of the graphical representation and the placement of the ascendant in the horoscope as documented in earlier articles on Roman Astrology.

During the rediscovery of astrology in the West in the Middle Ages, the practice of this nascent astrology incorporated the essential mistake of Ptolemy. Moreover, as astronomy began to develop into a proper science, even the modern view of astrology recast it as a quasi scientific law of physical causality, as opposed to a law of mysterious karma. Moreover, since Christianity of the fourth century had taken a hostile view of astrology, it had already then been pushed into the shadows and been slowly taken over by lesser practitioners. During the final centuries of the Roman empire astrology had become something of an art for swindlers, soothsayers and fortunetellers. By comparison, in India, astrology kept its moorings in a God centered world view including the theory of karma and the saintliness of the practitioner.

Isolation of Europe in the Middle Ages
To understand this development further we should note that following the fall of the Western Roman Empire in 476, the Middle Ages were born. This was a period of European history until the 15th century when the early Modern Era began. The term "Middle Ages" was coined in the 15th century and reflects the view that this period was a deviation from the path of classical learning, a path supposedly reconnected by Renaissance scholarship.[2] A part of this period, the early middle ages, has been termed the "Dark Ages“, noted for its cultural and economic deterioration as well as the major disruption in Western Europe. Importantly, the singular outside contact of European civilization was with early Islam of the Middle East and Northern Africa, and not India.[3] While this civilisation had protected some of the knowledge of the Roman and Greek worlds, it proved to be a not so hospitable to its internal consistency, by subjecting it to further speculative development.

To compound the problems further, astrology, had begun to fall out of favour in Rome as early as 321 A.D., when the Christian Emperor Constantine issued an edict threatening all Chaldeans, Magi, and their followers with death. As a result astrology disappeared for centuries from the Christian parts of Western Europe. Moreover, the early Christian legend distinguished between astronomy and astrology by ascribing the introduction of the former to the good angels and to Abraham while the latter was ascribed to Cham. Around this time, St. Augustine (354 – 430 A.D.), one of the most important figures in the development of Western Christianity, became active in the fight against astrology, moulding attitudes towards it for centuries to come. Even in Britain of the Enlightenment the practice of astrology was outlawed. Meanwhile, the original Vedic science of astrology has remained a part and parcel of Hindu society and is even openly taught at the university level.

Muslim invasions
The general decline of Western Civilisation during the Early Middle Ages was marked by trends of depopulation, deurbanization and increased barbarian invasion. North Africa and the Middle East, once part of the Eastern Roman Empire, were conquered by Islam. The islamisation of Spain took place from the beginning of the 8th century AD to the end of the 15th. Al-Andalus was the Arabic name given to a nation in the parts comprising most of what is now Spain and Portugal and governed by Berbers and African Muslims (given the generic name of Moors), at various times in the period between 711 and 1492.[4] The Moors were religious fanatics who subjugated these European territories as a part of the caliph of Damascus which was the capital of the Muslim world. Already in the 8th century the Christian Reconquest began, with the last vestiges of islam being pushed out in the Spanish Inquisition from 1478. The reaction resulted in the Crusades. In part, this cultural trend shows a singular focus of Westerners on the Biblical setting of the life story of Jesus Christ.

The Crusades
In the 10th century, the feudal system was established, which allowed a return to systemic agriculture. This trend was followed by sustained urbanization in northern and western Europe. During the High Middle Ages (c. 1000 – 1300 A.D.), Christian-oriented art and architecture flourished and Crusades were mounted to recapture the Holy Land.[5] The Roman Catholic Church sanctioned wars to be undertaken in pursuance of a vow and directed against infidels, i.e. against Muslims, pagans, heretics, or those under the ban of excommunication, called the Crusades. The specific crusades to restore Christian control of the Holy Land were fought over a period of nearly 200 years, between 1095 and 1291. Other campaigns in Spain and Eastern Europe continued into the 15th century. This exclusive interaction with the Arab world during the Middle Ages was only broken with the voyage of Columbus to the New World, but its influence has proved especially long lasting in the field of astrology.

Ptolemy made many contributions to science by documenting valuable astronomical, cartographical and astrological information. However, he was not an expert on horoscopic astrology or its history and his limited understanding of the visible zodiac of the fixed stars and constellations resulted in his adopting an erroneous astronomical representation of a moving zodiac, which, along with a removal from its authentic vedic source during the Middle Ages, had devastating implications for the development of astrology in the West, by undermining its efficacy as a true science of human karma. In fact, by altering the axiomatic principles of astrology itself, Ptolemy's mistake plunged Western astrology far into the shadows as the Age of Enlightenment rose. Fortunately, the classical principles of the original Greco-Indian horoscopic astrology were preserved in Hindu civilisation, even during the periods of Islamic (Mogul) and Christian (British) colonisation.

[1] Wikipedia: Ptolemy
[2] Wikipedia: Middle Ages
[3]"Archaeological Findings Point to Ancient Indo-Roman Trade". India Journal, July 15, 2010.
[4] Wikipedia: Al-Andalus
[5]Wikipedia: Crusades

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