Ptolemy and The Almugest

Klaudios Ptolemaios, or Ptolemy, lived and worked in Alexandria around 150 a.d. Although the precise dates and details of his life are unknown to us, his principal work, now commonly called the Almugest, supplies the evidence for placing him in the middle of the second century, for in this work he quotes his own observations of identifiable astronomical events.

Ptolemy did some work in pure mathematics, but he is famous as an applied mathematician. (It is, however, doubtful that he would have taken the modem distinction between pure and applied mathematics seriously.) His Almugest played the same role in mathematical astronomy as Euclid's Elements and Apollonius' Conics did in their respective subjects; it made its predecessors utterly superfluous, and so they are practically all lost. But Ptolemy, unlike Euclid, acknowledged his precursors' achievements generously and precisely, so our knowledge of pre-Ptolemaic astronomy is richer and firmer than our knowledge of pre-Euclidean mathematics. For the same reason, we can identify quite well Ptolemy's own contributions.

Mathematical astronomy is, by a wide margin, the oldest exact science. The Babylonians of the Seleucid Era, i.e. of the last three centuries b.c., had already devised elegant schemes yielding good quantitative predictions of astronomical phenomena. It is not surprising to anyone acquainted with Babylonian mathematics that these schemes are entirely arithmetical in nature, without a trace of underlying geometrical models; nor is it surprising that all serious attacks on astronomical problems in the Greek world are based on geometrical models.