Claudius Ptolemaeus (Ptolemy)

Flourished 146-Circa 170 c.e.

Georgrapher, astronomer, and mathematician

Sources

Speculations. Claudius Ptolema eus or Ptolemy, who wrote various works on astronomy and astrology, composed a geographical work (Geôgraphikê huphêgêsis, “Guide to Geography”) in eight books during the middle of the second century C.E. His method of deriving latitudes and longitudes from itineraries and days’ journeys (as opposed to incorporating these with astrological observation) yielded false measurements of the inhabited world. Although he was an astronomer, he depended on speculation rather than measurements of the earth based on astrology. He placed the Equator too far north, and his estimate of the circumference of the Earth was 30 percent less than the more accurate figure that had already been determined. Yet, despite these shortcomings, Ptolemy’s geographical work, which is extant, contains no less than twenty-six maps of various regions of the world, and one of the entire inhabited world. Ptolemy is the last notable ancient geographer in Europe before the voyages of Christopher Columbus and was considered a definitive source of geographical information until the fifteenth century.

Sources

J. L. E. Dreyer, A History of Astronomy from Thales to Kepler (New York: Dover, 1953).

Colin A. Ronan, Discovering the Universe: A History of Astronomy (New York: Basic Books, 1971).

J. O. Thomson, History of Ancient Geography (Cambridge: Cambridge University Press, 1948).