Ptolemy with an armillary sphere model, by Joos van Ghent and Pedro Berruguete, 1476.
Gallery of Claudius Ptolemy
1508
Sixteenth-century engraving of Claudius Ptolemy being guided by the muse of Astronomy, Urania - Margarita Philosophica by Gregor Reisch, published in 1508.
Gallery of Claudius Ptolemy
1596
Claudius Ptolemy, picture of 16th century book frontispiece by Theodor de Bry, 1596.
Gallery of Claudius Ptolemy
1662
A representation of Ptolemy from the Blaeu Atlas Maior (1662).
Sixteenth-century engraving of Claudius Ptolemy being guided by the muse of Astronomy, Urania - Margarita Philosophica by Gregor Reisch, published in 1508.
(One of the most important surviving ancient texts on Astr...)
One of the most important surviving ancient texts on Astrology. The Earth stood fixed at the center of the universe, with crystalline spheres within spheres whirling around it. In balance, the universe had a vast influence on earthly events, which was the basis for the belief in Astrology. This explanation stood for nearly a millennium and a half, bolstered by its acceptance as orthodoxy by the Catholic Church, until Copernicus and Galileo demolished it and placed the heliocentric (sun-centered) system in its place.
The Almagest: Introduction to the Mathematics of the Heavens
(The Almagest is by far the greatest work in astronomy in ...)
The Almagest is by far the greatest work in astronomy in ancient times. In a massive series of thirteen books, Ptolemy shows how every detail of the motions of the sun, moon, planets, and stars can be expressed using geometrical models that can be used to compute celestial positions with remarkable accuracy. The present selection covers all the essential features of Ptolemy's treatment of the heavens, omitting only more difficult and abstruse matters such as the moon's motion and the calculation of eclipses. In the interest of conciseness, the development of planetary theories is restricted to two planets, one inferior (Venus) and one superior (Mars). Ptolemy's text is accompanied by extensive notes and introductions that are aimed at making the book accessible to students encountering Ptolemy for the first time. This edition is designed to provide everything needed for a one-semester course, or it can be a component of a more general course on planetary theory or history of astronomy.
(Geography of Claudius Ptolemy, originally titled Geograph...)
Geography of Claudius Ptolemy, originally titled Geographia and written in the second century, is a depiction of the geography of the Roman Empire at the time. Though inaccurate due to Ptolemy's varying methods of measurement and use of outdated data, Geography of Claudius Ptolemy is nonetheless an excellent example of ancient geographical study and scientific method. This edition contains more than 40 maps and illustrations, reproduced based on Ptolemy's original manuscript. It remains a fascinating read for students of scientific history and Greek influence.
Claudius Ptolemy was an Egyptian astronomer, mathematician, and geographer of Greek descent. He flourished in Alexandria during the 2nd century. In several fields, his writings represent the culminating achievement of Greco-Roman science, particularly his geocentric model of the universe now known as the Ptolemaic system.
Background
Claudius Ptolemy was born around 100, in Egypt, Roman Empire. He probably lived on into the reign of Marcus Aurelius (161-180). It was claimed by Theodore Meliteniotes in around 1360 that Ptolemy was born in Hermiou (which is in Upper Egypt rather than Lower Egypt where Alexandria is situated) but since this claim first appears more than one thousand years after Ptolemy lived, it must be treated as relatively unlikely to be true. In fact, there is no evidence that Ptolemy was ever anywhere other than Alexandria.
His name, Claudius Ptolemy, is of course a mixture of the Greek Egyptian 'Ptolemy' and the Roman 'Claudius.' This would indicate that he was descended from a Greek family living in Egypt and that he was a citizen of Rome, which would be as a result of a Roman emperor giving that 'reward' to one of Ptolemy's ancestors.
Education
It is known that Ptolemy used observations made by Theon the Mathematician, and this was almost certainly Theon of Smyrna who almost certainly was his teacher. Certainly, this would make sense since Theon was both an observer and a mathematician who had written on astronomical topics such as conjunctions, eclipses, occultations, and transits. Most of Ptolemy's early works are dedicated to Syrus who may have also been one of his teachers in Alexandria, but nothing is known of Syrus.
If these facts about Ptolemy's teachers are correct then certainly in Theon he did not have a great scholar, for Theon seems not to have understood in any depth the astronomical work he describes. On the other hand, Alexandria had a tradition for scholarship which would mean that even if Ptolemy did not have access to the best teachers, he would have access to the libraries where he would have found the valuable reference material of which he made good use.
Career
Ptolemy was the author of numerous scientific treatises, at least three of which were of continuing importance to later Islamic and European science. The first was the astronomical treatise originally called He mathematike syntaxis ("The Mathematical Collection"), which came eventually to be known as Ho megas astronomos ("The Great Astronomer"). During the ninth century, Arab astronomers used the Greek superlative term Megiste for this work, which, when the definite article al was prefixed to it, became Almagest, the name by which it is generally known today. His second major work was Geographia, and a third of his noteworthy works was a set of books on geometry. He also wrote a treatise on astrology known as the Tetrabiblos, and additional works on music, optics, and other subjects.
The first chapter of Almagest, Ptolemy's most important work, contains a discussion of epistemology and philosophy. Two themes are paramount and woven together there: the organization of philosophy and his reason for studying mathematics. In the ancient period, "philosophy" included much more than is usually encompassed by that term today - it meant the whole of human knowledge and wisdom. The Almagest is divided into 13 books. Each of them deals with astronomical concepts concerning the stars and objects in the solar system.
A second of Ptolemy's influential works is his Geographia, a thorough discussion of the geographic knowledge of the Greco-Roman world. This, too, is a compilation of what was known about the world's geography in the Roman Empire during his time. He relied mainly on the work of an earlier geographer, Marinos of Tyre, and on gazetteers of the Roman and ancient Persian empires, but most of his sources beyond the perimeter of the Roman Empire were unreliable.
The first part of the Geographia is a discussion of the data and methods he used. As with the model of the solar system in the Almagest, Ptolemy put all this information into a grand scheme. He assigned coordinates to all the places and geographic features he knew, in a grid that spanned the globe. Latitude was measured from the equator, as it is today, but Ptolemy preferred to express it as the length of the longest day rather than degrees of arc. He put the meridian of 0 longitude at the westernmost land he knew, namely, the Canary Islands.
Ptolemy was a first-rate geometer and mathematician who devised important new geometrical proofs and theorems. In one book, entitled Analemma, he discussed projections of points on a celestial sphere. In another work, Planispherium, he studied stereographic projection, or the forms of solid objects represented on a plane. Another mathematical work was the two-book Hypothesis ton planomenon ("Planetary Hypothesis") in which he attempted, among other things, to give a proof of Euclid's parallel postulate.
Another of Ptolemy's noteworthy works is his treatise on astrology known as the Tetrabiblos ("Four books", derived from the Greek words tetra, meaning "four", and biblos, meaning "book"). The Tetrabiblos was the most popular astrological work of antiquity and also enjoyed great influence in the Islamic world and the medieval Latin West. It was continually reprinted. The great popularity of this treatise might be attributed to its exposition of the art of astrology and its being a compendium of astrological lore, rather than a manual. It speaks in general terms, avoiding illustrations and details of practice.
Ptolemy also wrote an influential work, Harmonics, on music theory.
Ptolemy's Optics is a work in five books that survives only as a poor Arabic translation. In it, he wrote about some of the properties of light, including reflection, refraction (the way light changes direction when passing from one medium to another of different density), and color. This was the first work on record that attempted to account for the observed phenomenon of the refraction of light. Recent attention to Ptolemy's Optics shows its sophisticated observational basis and that Ptolemy had conducted a series of carefully contrived experiments measuring refraction from air to water, air to glass, and water to glass.
Claudius Ptolemy established the system of mathematical astronomy that remained standard in Christian and Moslem countries until the 16th century. There are several characters or items named after Ptolemy, including the crater Ptolemaeus on the Moon; the crater Ptolemaeus on Mars; the asteroid 4001 Ptolemaeus; the Ptolemy Stone used in the mathematics courses at both US St. John's College campuses. Ptolemy's theorem on distances in a cyclic quadrilateral, and its generalization, Ptolemy's inequality, to non-cyclic quadrilaterals also bear his name.
(One of the most important surviving ancient texts on Astr...)
150
Religion
Ptolemy was a Greek pagan who held to the Greek pantheon of gods and the Greek understanding of the behavior and activity of the gods.
Views
In 13 books of the Almagest Ptolemy establishes kinematic models (purely mathematical and nonphysical) used to explain solar, lunar, and planetary motion and determines the parameters which quantify these models and permit the computation of longitudes and latitudes; of the times, durations, and magnitudes of lunar and solar eclipses; and of the times of heliacal risings and settings. Ptolemy also provides a catalog of 1, 022 fixed stars, giving for each its longitude and latitude according to an ecliptic coordinate system.
Ptolemy's is a geocentric system, though the earth is the actual center only of the sphere of the fixed stars and of the "crank mechanism" of the moon; the orbits of all the other planets are slightly eccentric. Ptolemy thus hypothesizes a mathematical system which cannot be made to agree with the rules of Aristotelian physics, which require that the center of the earth be the center of all celestial circular motions.
In solar astronomy, Ptolemy accepts and confirms the eccentric model and its parameters established by Hipparchus. For the moon, Ptolemy made enormous improvements in Hipparchus's model, though he was unable to surmount all the difficulties of lunar motion evident even to ancient astronomers. Ptolemy discerned two more inequalities and proposed a complicated model to account for them. The effect of the Ptolemaic lunar model is to draw the moon close enough to the earth at quadratures to produce what should be a visible increase in apparent diameter; the increase, however, was not visible. The Ptolemaic models for the planets generally account for the two inequalities in planetary motion and are represented by combinations of circular motions: eccentrics and epicycles. Such a combination of eccentric and epicyclic models represents Ptolemy's principal original contribution in the Almagest.
In the two books of Planetary Hypotheses, an important cosmological work, Ptolemy "corrects" some of the parameters of the Almagest and suggests an improved model to explain planetary latitude. In the section of the first book preserved only in Arabic, he proposes absolute dimensions for the celestial spheres (maximum and minimum distances of the planets, their apparent and actual diameters, and their volumes). The second book, preserved only in Arabic, describes a physical actualization of the mathematical models of the planets in the Almagest. Here the conflict with Aristotelian physics becomes unavoidable (Ptolemy uses Aristotelian terminology but makes no attempt to reconcile his views of the causes of the inequalities of planetary motion with Aristotle's), and it was in attempting to remove the discrepancies that the "School of Maragha" and also Ibn al-Shatir in the 13th and 14th centuries devised new planetary models that largely anticipate Copernicus's.
In the first book of the Apotelesmatica Ptolemy attempts to place astrology on a sound scientific basis. Astrology for Ptolemy is less exact than astronomy is, as the former deals with objects influenced by many other factors besides the positions of the planets at a particular point in time, whereas the latter describes the unswerving motions of the eternal stars themselves. In the second book, general astrology affecting whole states, societies, and regions is described; this general astrology is largely derived from Mesopotamian astral omina. The final two books are devoted to genethlialogy, the science of predicting the events in the life of a native from the horoscope cast for the moment of his birth.
In his book the Geography, that consists of eight books, Ptolemy sets forth mathematical solutions to the problems of representing the spherical surface of the earth on a plane surface (a map), but the work is largely devoted to a list of localities with their coordinates. Despite his brilliant mathematical theory of map making, Ptolemy had not the requisite material to construct the accurate picture of the world that he desired. Aside from the fact that, following Marinus in this as in much else, he underestimated the size of the earth, concluding that the distance from the Canaries to China is about 180° instead of about 130°, he was seriously hampered by the lack of all the gnomon observations that are necessary to establish the latitudes of the places he lists. For longitudes, he could not utilize astronomical observations because no systematic exploitation of this method of determining longitudinal differences had been organized. He was compelled to rely on travelers' estimates of distances, which varied widely in their reliability and were the most uncertain guides. His efforts, however, provided Western Europe, Byzantium, and Islam with their most detailed conception of the inhabited world.
Quotations:
"We consider it a good principle to explain the phenomena by the simplest hypothesis possible."
"Everything that is hard to attain is easily assailed by the generality of men."
"As material fortune is associated with the properties of the body, so honor belongs to those of the soul."
"There are three classes of friendship and enmity, since men are so disposed to one another either by preference or by need or through pleasure and pain."
Personality
Because of systematic errors in his works, Ptolemy is accused by some of just correcting Hipparchus' data for precession. Indeed, there is some evidence that Ptolemy is guilty of stealing and fabricating data. But he is still one of the most influential Greek astronomers and geographers of his time.
Quotes from others about the person
"Ironically, even when Copernicus' heliocentric theory had replaced the Ptolemaic system, many astronomers used Ptolemy's model to predict the motion of the planets, since its intricate calculations produced more accurate values." - David H. Clark & Matthew D. H. Clark, in Measuring the Cosmos: How Scientist Discovered the Dimensions of the Universe
Interests
Philosophers & Thinkers
Aristotle, Hipparchus
Connections
There is no information on whether Claudius Ptolemy was ever married or had any children.
