Claudius Ptolemaeus or Ptolemy
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The famous Egyptian mathematician, astronomer, geographer Claudius Ptolemaeus is known as Ptolemy. His period ranged from 90 to 170 C.E. he was associated with the city of Alexandria in Egypt.
Ptolemy is one of the ancient or classical Roman scholars. His major works includes the Almagest (The Great Treatise) on Mathematics; Geographia on geography and Terabiblos on astrology and philosophy.
Contribution of Ptolemy in the field of Astronomy
Ptolemy is known for his book Almagest. It is the only available work on ancient astronomy. Astronomical calculations of Ptolemy were based on observations provided by the ancient astronomers.
In the Almagest, Ptolemy has described many of his studies. In this book, Ptolemy has presented mathematical techniques to calculate the motion of stars and planets. In these treatises, he has also included a list of 48 constellations recognized by the Greeks and Romans astronomers.
Another book by Ptolemy on astronomy is known as Planetary Hypotheses, in which he used a mathematical model to determine the size of the universe. Ptolemy calculated the positions of the Sun, Moon and other planets as well as eclipses.
Contribution of Ptolemy to Geography
Along with astronomy, Ptolemy was also a known for his contributions in geography. His book, Geographia is a compilation of all the major works done on geography in ancient times. In this Ptolemy compiled all known descriptions about the geography of the known world up to the second century.
Ptolemy first divided the earth into grids. In Geographia, Ptolemy gave instructions for making accurate maps and presented many maps of the world known at the time of the Greek and Roman Empires.
The Geographia consisted of eight volumes;
- The first volume of the treatise describes the problems of representing a spherical earth on a flat two-dimensional sheet of paper and provides information about map projections.
- The second to seventh volumes of these treatises were a collection of eight thousand places around the world. In this gazetteer, Ptolemy has presented the latitude and longitude of all the places. He was the first to introduce a map based on a grid system. The geographical knowledge of the Romans is revealed by the collection of their place names and their coordinates.
- The last section of Geographia was an atlas, characterized by the use of a grid system for those maps. These maps carried the north at the top of all maps. This is a cartographic convention created by Ptolemy.
Evaluation of Contributions of Ptolemy
Ptolemy not only mapped the known world but also the known universe. It is a great contribution in the field of cosmology. He considered and mapped the Earth as the centre of the universe. This geocentric model of the universe is also known as Ptolemy’s system. This system was recognized as the dominant cosmological system throughout the ancient world, including Ancient Greece and Ancient Roman world.
The greatest contribution of Ptolemy was not the map itself, but the concepts behind the maps. He introduced three different methods of map projections and provided coordinates of all the geographic features he knew of over 8000 places. He invented the concept of latitude and longitude. The mapping system introduced by Ptolemy is generally still in use.
The book Guide to Geography is often considered as the beginning of the modern science of cartography or map-making. The significance of the Guide to Geography is that Ptolemy first used the system of latitude and longitude to indicate places on a map.
The expansion of the known world from the Canary Islands to the Gulf of Thailand was documented in the maps of Ptolemy. Marco Polo and Christopher Columbus both used his maps as the basis for their own explorations around the world.
Mapping Errors of Ptolemy
The map work or mapping of Ptolemy had a significant impact on the geographical understanding of the world in the Renaissance period. But Ptolemy disagreed with estimates of Eratosthenes of the circumference of the Earth. He accepted the circumference of the Earth as 18000 miles in place of the estimate of Eratosthenes of 25000 miles. It was a smaller circumference that led Christopher Columbus to believe that he could travel west from Europe to Asia. Ptolemy greatly underestimated the distance of the Atlantic Ocean from Spain to India. In addition, Ptolemy depicted the Indian Ocean as a large inland sea, bounded to the south by the Terra Incognita. All these estimates were factually incorrect.
In spite of all these shortcomings, indisputably Ptolemy made an important contribution to the development of geographical knowledge.