BIOGRAPHY
Claudius Ptolemy (c. 100 – c. 170) was a mathematician, astronomer, geographer and astrologer who wrote several scientific treatises, three of which were of importance to later Byzantine, Islamic and Western European science. The first is the astronomical treatise now known as the Almagest, although it was originally entitled the Mathematical Treatise (Μαθηματικὴ Σύνταξις) and then known as The Great Treatise (Ἡ Μεγάλη Σύνταξις). 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 in which he attempted to adapt horoscopic astrology to the Aristotelian natural philosophy of his day. This is sometimes known as the Apotelesmatiká (Ἀποτελεσματικά) but more commonly known as the Tetrábiblos from the Koine Greek (Τετράβιβλος) meaning “Four Books” or by the Latin Quadripartitum.
Ptolemy lived in the city of Alexandria in the Roman province of Egypt under the rule of the Roman Empire, had a Latin name (which several historians have taken to imply he was also a Roman citizen), cited Greek philosophers, and used Babylonian observations and Babylonian lunar theory. The 14th century astronomer Theodore Meliteniotes gave his birthplace as the prominent Greek city Ptolemais Hermiou (Πτολεμαΐς ‘Ερμείου) in the Thebaid (Θηβᾱΐς). This attestation is quite late, however, and there is no other evidence to confirm or contradict it. He died in Alexandria around 168.
EARLY LIFE
Ptolemaeus (Πτολεμαῖος Ptolemaîos) is an ancient Greek personal name. It occurs once in Greek mythology and is of Homeric form. It was common among the Macedonian upper class at the time of Alexander the Great and there were several of this name among Alexander’s army, one of whom made himself pharaoh in 323 BCE: Ptolemy I Soter, the first pharaoh of the Ptolemaic Kingdom. All subsequent pharaohs of Egypt until Egypt became a Roman province in 30 BCE, ending the Macedonian family’s rule, were also Ptolemies.
The name Claudius is a Roman name, belonging to the gens Claudia; the peculiar multipart form of the whole name Claudius Ptolemaeus is a Roman custom, characteristic of Roman citizens. Several historians have made the deduction that this indicates that Ptolemy would have been a Roman citizen. Gerald Toomer, the translator of Ptolemy’s Almagest into English, suggests that citizenship was probably granted to one of Ptolemy’s ancestors by either the emperor Claudius or the emperor Nero.
The 9th century Persian astronomer Abu Maʻshar presents Ptolemy as a member of Egypt’s royal lineage, stating that the descendants of the Alexandrine general and Pharaoh Ptolemy I Soter, were wise “and included Ptolemy the Wise, who composed the book of the Almagest”. Abu Maʻshar recorded a belief that a different member of this royal line “composed the book on astrology and attributed it to Ptolemy”. We can evidence historical confusion on this point from Abu Maʿshar’s subsequent remark: “It is sometimes said that the very learned man who wrote the book of astrology also wrote the book of the Almagest. The correct answer is not known.” Not much positive evidence is known on the subject of Ptolemy’s ancestry, apart from what can be drawn from the details of his name (see above), although modern scholars have concluded that Abu Maʻshar’s account is erroneous. It is no longer doubted that the astronomer who wrote the Almagest also wrote the Tetrabiblos as its astrological counterpart.
Ptolemy wrote in ancient Greek and can be shown to have utilized Babylonian astronomical data. He might have been a Roman citizen, but was ethnically either a Greek or a Hellenized Egyptian. He was often known in later Arabic sources as “the Upper Egyptian”, suggesting he may have had origins in southern Egypt. Later Arabic astronomers, geographers and physicists referred to him as Baṭlumyus (Arabic: بَطْلُمْيوس).
ASTRONOMY
Ptolemy’s Almagest is the only surviving comprehensive ancient treatise on astronomy. 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. The Almagest also contains a star catalogue, which is a version of a catalogue created by Hipparchus. Its list of forty-eight constellations is ancestral to the modern system of constellations, but unlike the modern system they did not cover the whole sky (only the sky Hipparchus could see). Across Europe, the Middle East and North Africa in the Medieval period, it was the authoritative text on astronomy, with its author becoming an almost mythical figure, called Ptolemy, King of Alexandria. The Almagest was preserved, like most of extant Classical Greek science, in Arabic manuscripts (hence its familiar name). Because of its reputation, it was widely sought and was translated twice into Latin in the 12th century, once in Sicily and again in Spain. Ptolemy’s model, like those of his predecessors, was geocentric and was almost universally accepted until the appearance of simpler heliocentric models during the scientific revolution.
His 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 1,210 Earth radii, while the radius of the sphere of the fixed stars was 20,000 times the radius of the Earth.
Ptolemy presented a useful tool for astronomical calculations in his Handy Tables, which 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. Ptolemy’s Handy Tables provided the model for later astronomical tables or zījes. In the Phaseis (Risings of the Fixed Stars), Ptolemy gave a parapegma, a star calendar or almanac, based on the appearances and disappearances of stars over the course of the solar year.
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