Information AboutPtolemy |
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Claudius Ptolemaeus ( – c. 168 ), known in English as '''Ptolemy''', was a Geographer , Astronomer , and Astrologer who lived in the Hellenistic Culture of Roman Egypt . He may have been a Hellenized Egyptian but no description of his family background or physical appearance exists, though it is likely he was born in Egypt. Ptolemy was the author of several scientific treatises, three of which have been of continuing importance to later Islamic and European science. The first is the astronomical treatise that is now known as the Almagest (in Greek ''Η μεγάλη Σύνταξις'', "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. NAME ''Claudius'' is a Roman name. Claudius Ptolemy was almost certainly a Roman citizen, and he or his ancestor adopted the '' Nomen '' of a Roman called Claudius, who was in some sense responsible for the citizenship. If, as was not uncommon, this Roman was the Emperor, the citizenship would have been granted between 14 and 68 AD . The astronomer would also have had a '' Praenomen '', which we do not know. '' Ptolemy '' is a Greek name. It occurs once in Greek mythology, and is of Homeric form. It was quite common among the Macedonian upper class at the time of Alexander The Great , and there are several among Alexander's army, one of whom made himself King of Egypt; all the Kings after him, until Rome conquered Egypt, were also Ptolemies. Whether the astronomer's name represents royal blood, loyalty, or chance is also not known. Ptolemy read, and wrote in, Greek; he used Babylonian data, probably in translation. he worked in Alexandria, which was a primarily Greek and Jewish city on the edge of Egypt; there is relatively little evidence of native Egyptian inhabitants. ASTRONOMY In the '' Almagest '', one of the most influential books of Classical Antiquity , Ptolemy compiled and extended the astronomical knowledge and theories of the ancient Greek and Babylonian world; he relied mainly on the work of Hipparchus of three centuries earlier. It was preserved, like most of Classical Greek science, in Arabic manuscripts (hence its familiar name) and only made available in Latin translation (by Gerard Of Cremona ) in the 12th Century . Ptolemy formulated a Geocentric model that was widely accepted until it was superseded by the Heliocentric Solar System of Copernicus . Likewise his computational methods (supplemented in the 12th century with the Arabic computational '' Tables Of Toledo '') were of sufficient accuracy to satisfy the needs of astronomers, astrologers and Navigator s, until the time of the great explorations. They were also adopted in the Arab world and in India . The ''Almagest'' also contains a Star Catalogue , which is probably an updated version of a catalogue created by Hipparchus. Its list of forty-eight Constellation s is ancestral to the modern system of constellations, but unlike the modern system they did not cover the whole sky (only the sky Ptolemy could see). The ''Almagest'' is also known as the ''Great Syntaxis of Astronomy''. 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. GEOGRAPHIA See Also: Geographia (Ptolemy) Ptolemy's other main work is his ''Geographia''. 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 Gazetteer s of the Roman and ancient Persian Empire , but most of his sources beyond the perimeter of the Empire were unreliable. The first part of the ''Geographia'' is a discussion of the data and of the methods he used. Like with the model of the solar system in the ''Almagest'', Ptolemy put all this information into a grand scheme. He assigned Coordinate s 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 (the length of the Midsummer day increases from 12h to 24h as you go from the equator to the Polar Circle ). He put the Meridian of 0 Longitude at the most western land he knew, the Canary Islands . , reconstituted from Ptolemy's ''Geographia'' (circa 150 ), indicating the countries of " Serica " and "Sinae" ( China ) at the extreme right, beyond the island of "Taprobane" ( Sri Lanka , oversized) and the "Aurea Chersonesus" ( Malay Peninsula ).]] Ptolemy also devised and provided instructions on how to create maps both of the whole inhabited world (''oikoumenè'') and of the Roman provinces. In the second part of the ''Geographia'' he provided the necessary Topographic lists, and captions for the maps. His ''oikoumenè'' spanned 180 degrees of longitude from the Canary islands in the Atlantic Ocean to the middle of China , and about 80 degrees of latitude from the Arctic to the East Indies and deep into Africa ; Ptolemy was well aware that he knew about only a quarter of the globe, and he knew that his information did not extend to the Eastern Sea. The maps in surviving manuscripts of Ptolemy's ''Geographia'', however, date only from about 1300, after the text was rediscovered by Maximus Planudes . It seems likely that the topographical tables in books 2-7 are cumulative texts - texts which were altered and added to as new knowledge became available in the centuries after Ptolemy (Bagrow 1945). This means that information contained in different parts of the Geography is likely to be of different date. found 700 ''stadia'' for a degree on the globe, in the ''Geographia'' Ptolemy uses 500 ''stadia''. It is not certain if these geographers used the same ''stadion'', but there is no ''direct'' evidence of more than one value of the ''stadion''. If they both used the traditional Olympic ''stadion'' of about 185 meters, then the older estimate is 1/6 too large, and Ptolemy's value is 1/6 too small. Because Ptolemy derived most of his topographic coordinates by converting measured distances to angles, his maps get distorted. So his values for the latitude were in error by up to 2 degrees. For longitude this was even worse, because there was no reliable method to determine geographic longitude; Ptolemy was well aware of this. It remained a problem in geography until the invention of Chronometer s at the end of the 18th century. It must be added that his original topographic list cannot be reconstructed: the long tables with numbers were transmitted to posterity through copies containing many scribal errors, and people have always been adding or improving the topographic data: this is a testimony to the persistent popularity of this influential work. In his ''Optics'', a work which survives only in a poor Arabic translation, he writes about properties of Light , including Reflection , Refraction and Colour . His other works include ''Planetary Hypothesis'', ''Planisphaerium'' and ''Analemma''. ASTROLOGY Ptolemy's treatise on Astrology , the ''Tetrabiblos'', was the most popular astrological work of antiquity and also enjoyed great influence in the Islamic world and the Medieval Latin West . The ''Tetrabiblos'' is an extensive and continually reprinted treatise on the ancient principles of Horoscopic Astrology in four books (Greek ''tetra'' means "four", ''biblos'' is "book"). That it did not quite attain the unrivalled status of the ''Syntaxis'' was perhaps because it did not cover some popular areas of the subject, particularly Horary Astrology (interpreting astrological charts for a particular moment to determine the outcome of a course of action to be initiated at that time), Electional Astrology , and Medical Astrology . 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, avoiding illustrations and details of practice. Ptolemy was concerned to defend astrology by defining its limits, Compiling Astronomical Data that he believed was reliable and dismissing practices (such as considering the Numerological significance of names) that he believed to be without sound basis. Much of the content of the ''Tetrabiblos'' may well have been 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. It is, indeed, presented as the second part of the study of astronomy of which the ''Syntaxis'' was the first, concerned with the influences of the celestial bodies in the Sublunar sphere. Thus explanations of a sort are provided for the astrological effects of the Planets , based upon their combined effects of heating, cooling, moistening, and drying. Ptolemy's astrological outlook was quite practical: he thought that astrology was like , Country , and Upbringing of a person affects an individual's personality as much if not more than the positions of the Sun, Moon, and planets at the precise moment of their birth, so Ptolemy saw astrology as something to be used in life but in no way relied on entirely. MUSIC Ptolemy also wrote an influential work, ''Harmonics'' on Music Theory . After criticizing the approaches of his predecessors, Ptolemy argued for basing musical intervals on mathematical ratios (in contrast to the followers of Aristoxenus ) backed up by empirical observation (in contrast to the overly-theoretical approach of the Pythagoreans ). He presented his own divisions of the Tetrachord and the Octave , which he derived with the help of a Monochord . Ptolemy's astronomical interests also appeared in a discussion of the Music Of The Spheres . OTHER WORKS In his ''Optics'', a work which survives only in a poor Arabic translation, he writes about properties of Light , including Reflection , Refraction and Colour . His other works include ''Planetary Hypothesis'', ''Planisphaerium'' and ''Analemma''. NAMED AFTER PTOLEMY
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