Ptolemy

:''This article is about the geographer and astronomer Ptolemy. For Alexander the Great's general, see Ptolemy I of Egypt. For others named "Ptolemy" or "Ptolemaeus", see Ptolemy (disambiguation).'' [[image:Ptolemy.jpg|thumb|240px|Claudius Ptolemaeus, given contemporary German styling, in a 16th century engraved book frontispiece]] Claudius Ptolemaeus (Greek language: Κλαύδιος Πτολεμαῖος; c. 85 – c. 165), known in English as Ptolemy, was a Hellenistic civilization geographer, astronomer, and astrologer who probably lived and worked in Alexandria in Egypt. Ptolemy was the author of two important scientific treatises. One is the astronomical treatise that is now known as the Almagest (in Greek ''Η μεγάλη Σύνταξις'', "The Great Treatise"). 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. In this work, one of the most influential books of Antiquity, Ptolemy compiled the astronomical knowledge of the ancient Greek and Babylonian world; he relied mainly on the work of Hipparchus of three centuries earlier. Ptolemy formulated a geocentric model (see: Ptolemaic system) of the solar system which remained the generally accepted model in the Western and Arab worlds until it was superseded by the heliocentric solar system of Copernicus.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 navigators, 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 48 constellation is ancestral to the modern system of constellations, but unlike the modern system they did not cover the whole sky. Ptolemy's other main work is his ''Geography''. This too is a compilation, of what was known about the world's geography in the Roman empire at his time. He relied mainly on the work of an earlier geographer, Marinos of Tyre, and on gazetteers 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 ''Geography'' 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 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 in 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. [[Image:PtolemyWorldMap.jpg|thumb|300px|The Ptolemy world map, reconstituted from Ptolemy's ''Geographia'' (circa 150), indicating "Sinae" (China) at the extreme right, beyond the island of "Taprobane" (Sri Lanka, oversized) and the "Aurea Chersonesus" (Southeast Asian peninsula).]] Ptolemy also devised and provided instructions on how to create maps both of the whole inhabited world (''oikoumen�'') and of the Roman provinces. In the second part of the ''Geography'' he provided the necessary topographic lists, and captions for the maps. His ''oikoumen�'' spanned 180 degrees of longitude from the Canary islands in the Atlantic Ocean to 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. The maps in surviving manuscripts of Ptolemy's ''Geography'' however, date only from about 1300, after the text was rediscovered by Maximus Planudes. Maps based on scientific principles had been made since the time of Eratosthenes (3rd century BC), but Ptolemy invented improved projections. It is known that a world map based on the ''Geography'' was on display in Autun (France) in late Roman times. In the 15th century Ptolemy's ''Geographia'' began to be printed with engraved maps; an edition printed at Ulm in 1482 was the first one printed north of the Alps. The maps look distorted as compared to modern maps, because Ptolemy's data were inaccurate. One reason is that Ptolemy estimated the Earth too small: while Eratosthenes 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 if we assume that they both stuck to the traditional Attic ''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 chronometers at the end of the 18th century AD. 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 of 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''. ==Ptolemy and 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 Western world. The ''Tetrabiblos'' is an extensive and continually reprinted treatise on the ancient priciples of 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 astrological 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 rationalised. 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 Earth 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 practical: astrology was like medicine; conjectural, because of the many variable factors to be taken into account: the race, country, nurture, and so forth, of the individual. Some events are fated, others are not, and some occur as the result of general circumstances, not those of the individual. ==Ptolemy and 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. ==Named after Ptolemy== *Ptolemaeus (Lunar crater) on the Moon. *Ptolemaeus (crater) on Mars (planet). ==References== *Berggren, J. Lennart and Jones, Alexander. 2000. ''Ptolemy's Geography: An Annotated Translation of the Theoretical Chapters''. Princeton University Press. Princeton and Oxford. ISBN: 0-691-01042-0. *Stevenson, Edward Luther. Trans. and ed. 1932. ''Claudius Ptolemy: The Geography''. New York Public Library. Reprint: Dover, 1991. (This is the only complete English translation of Ptolemy's most famous work. Unfortunately, it is marred by numerous mistakes and the placenames are given in Latinised forms, rather than in the original Greek). ==External links== ===Primary sources=== *[http://penelope.uchicago.edu/Thayer/E/Roman/Texts/Ptolemy/Tetrabiblos/home.html Ptolemy's Tetrabiblos at LacusCurtius] (English translation, with introductory material) *[http://penelope.uchicago.edu/Thayer/E/Gazetteer/Periods/Roman/_Texts/Ptolemy/home.html Ptolemy's Geography at LacusCurtius] (English translation, incomplete) ===Secondary material=== *[http://www.skyscript.co.uk/ptolemy.html Ptolemy at SkyScript] - ''The Life and Work of Ptolemy'' *[http://www.chass.utoronto.ca/~ajones/ptolgeog/ Alexander Jones, "Ptolemy and his ''Geography''"] *[http://obs.nineplanets.org/psc/theman.html Ptolemy biography] (Bill Arnett's site) *[http://wwwuser.gwdg.de/~fhasele/ptolemaeus/index.html Ptolemy's Geography of Asia] - Selected problems of Ptolemy's Geography of Asia (currently in German) *[http://www.fiks.de/rom/index.htm?rom10.htm Ptolemy's Geography of Northwestern Europe] ==See also== *Astrology *Deferent and epicycle *History of astrology *History of astronomy Ancient Greeks Polymaths Greek and Roman astronomers Greek and Roman astrologers Greek cartographers Roman era geographers Constellations listed by Ptolemy 85 births 165 deaths fa:بطلمیوس

Ptolemy

I wrote a nice article about Ptolemy's sky theory on everything [http://www.everything2.com/?node=ptolemaic+system here]. Where should it go? Under "Ptolemy", "Ptolemaic System", or "Almagest"? For now I'll put it in Almagest... - TOGoS ---- Claudius Ptolemy "The Geography" in English language has been first published by Dover Publications, Inc , New York in 1991 . It is now available at amazon.com and other book stores. This is an unabridged republication of the work originally published by The New York Public Library, N.Y. in 1 9 3 2. At that time it was translated and edited by Edward Luther Stevenson. Although Ptolemie's "Geography" was well known in Europe for almost 1900 years , 1932 was the first time ever of its translation into English. (User:Conversion script) :A word to the wise: that translation is very, very bad, and cannot be relied on for much of anything. (It is a poor translation of not the original Greek, but of Karl M�ller's Latin translation, with errors of every conceivable kind, including egregious typos and other corruptions.) Considering that most of the Geography consists of a mere index of placenames, you're far better off reading the original Greek, even if you just have limited Greek. It's the Stevenson translation that I started putting online on my iste (referenced as the external link in the article), but as it became more and more apparent to me just how bad it was, I just abandoned it. User:Bill Thayer 11:34, 15 Jun 2005 (UTC) == Ptolemy == Why is the "p" not pronounced? the circa date of birth and death are not labeled as bc or ad. Which is it? :Presumably "pt" was originally pronounced, but we find it difficult to do so, so the "p" is silent in English. :If it's not labeled BC or AD, then by default it's AD. Just like 2005 is 2005 AD. Note: My understanding is that the Ptolemy incorrectly estimated the actual size of the Earth by almost half, but the article claims "he was well aware" that he only had a quarter of it mapped. Does someone have evidence to confirm or deny the article's position? Thanks, Griff ::Yes; we all do. His Geography gives latitudes and longitudes of all the places mapped: the farthest east he gives is "180°", measured from what he feels is his farthest point west; the farthest north he gives is 62°30, the farthest south is 8°25. He doesn't wear it on his sleeve, then, but he realizes perfectly well he covers at very best only (180/360 * 71/180) of the globe. User:Bill Thayer 20:36, 7 Jun 2005 (UTC) == Image of Ptolemy at Top == Though it is indicated that the image represents a 16th century adaptation of him, the image should still be eventually removed and replaced by a much more realistic image of Ptolemy. User:Decius 03:38, 15 Apr 2005 (UTC) :Good luck!!! This would be a major historical find.... User:Bill Thayer 07:34, 9 Jun 2005 (UTC) Must be a joke, User: Bill Thayer. I've seen more accurate artist's representations of Ptolemy before. There is one, for example, in this book I have, which is much closer to reality than the current image (closer to reality if only by the fact that he is depicted as a Greek of his time, not a 16th century German). User:Decius 07:15, 15 Jun 2005 (UTC) :No joke, Decius. Costume doesn't make the portrait of a person any more realistic, and there is no contemporary portrait of him, nor any verbal description. This fanciful picture is as good as another.... User:Bill Thayer 11:16, 15 Jun 2005 (UTC) But that's where I disagree. The costume, style, and look of other images available (such as some I've seen) are more accurate, just by the fact that he's not in 16th century garb. User:Decius 12:43, 15 Jun 2005 (UTC) Oh well, I guess you're just defending that image because you like it or gotten used to it. I don't have another image available for upload anyway. I just think its style is not what's needed, in the sense that it doesn't "create the mood" or fit his era. User:Decius 12:51, 15 Jun 2005 (UTC) == Ptolemy's Canon == In the July/August issue of Archeology Odyssey, there is a fascinating article "How to date a Pharaoh." It discusses howdates of ancient events can be determined, and it discusses the history of trying to determine the dates of ancient events. One important document that had great impact on accurate dating of events going back to ca. 700 B.C. was a kings' list named "Ptolemy's Canon." It became known in the West in a defective form in the 16th century, but more copies have since come to light. Rather than go on about the matter, I will just refer folks to the article. At any rate, it seems that an entry for Ptolemy's Canon might be in order. Jim Oppenheimer Hyde Park, NY jwally@prodigy.net

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