2nd-century Roman mathematician, astronomer, geographer

Claudius Ptolemaeus (Greek: Κλαύδιος Πτολεμαῖος; c. 100c. 170), known in English as Ptolemy, was an ancient Greek geographer, astronomer, and astrologer who probably lived and worked in Alexandria, off the coast of Egypt.

Everything that is hard to attain is easily assailed by the generality of men.




  • I know that I am mortal by nature and ephemeral, but when I trace at my pleasure the windings to and fro of the heavenly bodies, I no longer touch earth with my feet. I stand in the presence of Zeus himself and take my fill of ambrosia.
    • In some of the manuscripts, the books begins with this epigram (Owen Gingerich, The Eye of Heaven: Ptolemy, Copernicus, Kepler, American Institute of Physics, 1993, p. 55).
  • We consider it a good principle to explain the phenomena by the simplest hypothesis possible.
    • Book III, sec 1 (trans. Gerald J. Toomer)


  • πᾶν μὲν τὸ δυσέφικτον παρὰ τοῖς πολλοῖς εὐδιάβλητον ἔχει φύσιν
    • Everything that is hard to attain is easily assailed by the generality of men.
    • Book I, sec. 1
  • The length of life takes the leading place among inquiries about events following birth.
    • Book III, sec. 10
  • As material fortune is associated with the properties of the body, so honor belongs to those of the soul.
    • Book IV, sec. 1
  • 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.
    • Book IV, sec. 7

About Ptolemy

  • Ptolemy's Geography is the only book on cartography to have survived from the classical period and one of the most influential scientific works of all time.
    • J. Lennart Berggren and Alexander Jones, in Ptolemy's Geography: An Annotated Translation of the Theoretical Chapters (2001)
  • He left in his Optics, the earliest surviving table of angles of refraction from air to water. ...This table, quoted and requoted until modern times, has been admired... A closer glance at it, however, suggests that there was less experimentation involved in it than originally was thought, for the values of the angles of refraction form an arithmetic progression of second order... As in other portions of Greek Science, confidence in mathematics was here greater than that in the evidence of the senses, although the value corresponding to 60° agrees remarkably well with experience.
  • Ptolemy... against the champions of this or that cosmology of the heavens... had dared to claim that it is legitimate to interpret the facts of astronomy by the simplest geometrical scheme which will 'save the phenomena,' no matter whose metaphysics might be upset. His conception of the physical structure of the earth, however, prevented him from carrying through in earnest this principle of relativity, as his objections to the hypothesis that the earth moves amply show.
  • Claudius Ptolemy's great contribution to astronomy was his famous work the Almagest, which presented formally the astronomical theories of the day that had evolved from the great debates within the different Greek philosophical schools. Claudius Ptolemy freely admitted that he had contributed little original research to the treatise but rather had based his conclusions principally on the work of Hipparchus. ...Ptolemy did not claim that his cosmological model described the actual conditions. It simply reproduced geometrically the observed motions of the known heavenly bodies and enabled their positions to be easily predicted for any particular time. … 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 (2004)
  • To give here an elaborate account of Pappus would be to create a false impression. His work is only the last convulsive effort of Greek geometry which was now nearly dead and was never effectually revived. It is not so with Ptolemy or Diophantus. The trigonometry of the former is the foundation of a new study which was handed on to other nations indeed but which has thenceforth a continuous history of progress.
  • Copernicus, Kepler and Galileo were ‘revisionists’ in rejecting the geocentric system of Ptolemy (which held sway for some 1500 years) and, against an oppressive and repressive mainstream opinion (and officialdom), reinstated—with improvements—the heliocentric system of Aristarchos of Samos (3rd cent BCE).
    • Kazanas, N. (2002). Indigenous Indo-Aryans and the Rigveda: Indo-Aryan migration debate. Journal of Indo-European Studies, 30(3-4), 275-334.
Wikipedia has an article about:
Wikimedia Commons has media related to: