Ptolemy's Almagest

Before buying Ptolemy’s Almagest (written around A.D. 150) I knew of its reputation as a highly technical and difficult text on Greek geocentric astronomy. Still, the extremely thorough treatment by Ptolemy with all its details surprised me, and I really admire the achievements by Ptolemy and his ancestors.I couldn’t have done much progress without two excellent commentaries. Olaf Pedersen’s “A Survey of the Almagest” (with annotation and new commentary by Alexander Jones, Springer, 2010) was very helpful in revealing the mathematical aspects in Almagest. Even more important for me was James Evans’ “The History and Practice of Ancient Astronomy” (Oxford University Press, 1998) since Evans both explained the historical background of Almagest and helped in several mathematical details. An armillary sphere would also have been very helpful in getting a concrete view of the rotations. I didn’t have it, but I made a primitive prototype from a metal wire. With the help of these tools I managed to get a fairly clear picture of the Books I-IV, ca. 200 pages on Ptolemy’s mathematical tools and on solar and lunar motions, in ca. 2.5 months (after normal working days and on weekends). Thereafter, I spent ca. 3 weeks for a fairly superficial overview of the rest of the book. I got what I wanted: a basic understanding of Almagest.Here are two of my favourite passages. On pages 153-156 Ptolemy shows a “curve fitting” on solar motion. He demonstrates how the parameters of eccentric model are adjusted to match the calculated intervals between equinoxes and solstices with the observations by Hipparchus. On page 206 he describes the attitude of a real scientist: “For those who approach this science in a true spirit of enquiry and love of truth ought to use any new methods they discover, which give more accurate results, to correct not merely the ancient theories, but their own too, if they need it. They should not think it disgraceful, when the goal they profess to pursue is so great and divine, even if their theories are corrected and made more accurate by others beside themselves.”

The main desire of Ptolemy in writing his Almagest is to explain and account for the motions of the apparently erratic celestial beings in terms of perfect and circular motions. In doing so he introduces the epicyclic (which states that the center of a smaller circle orbits around the earth and the object orbits around the smaller circle) and the eccentric hypotheses (which supposes that the center of the circular motion of the planet is not exactly centered on the earth), which are ultimatly equivalent to eachother in terms of result. Begining with the motion of the sun in the sky and moving on to the less accountable outer planets, Ptolemy moves his mathematics brilliantly with a nod to a story teller's art. Some may find his introduction of his equant (something that is often said to defile his principles of perfect motion), which explains the retrogradation of the outer planets, to be a let down to the fanfare of perfection in the stars. Yet, overall, the Almagest manages to recapture the magic and wonder of the universe through complicated mathematical hypotheses and to succesfully lay the ground for the break throughs of Copernicus, Brahe, and Kepler to come. If you are at all interested in astronomy or mathematics, you ought to read this.

It was just what I needed for my college class.

It's a very interesting astronomy book, it's explain how they've thought about the motion of the planets(epicycles)in the past(AC)by the time of the Ptolemy and Babylonia.

Adding to the other comment below about star names beginning with "al-," I might add that the title "Almagest" itself is an Arabic translation of the original Greek "Megale Syntaxis."

so it turns out that the center of the eccentric circle that the planets travel on travels on its own circle but be careful this is not a giant epicycle on a small deferent! haha! genius!!

Der Almagest ist ein für die Grundlagen der Mathematik, Astronomie und Kosmologie nicht hoch genug einzuschätzendes Werk. Um so schöner ist es, daß es Toomer in hervorragender Weise gelungen ist, dieses Meisterwerk noch durch editorische Arbeit weiter zu veredeln! Aber Vorsicht: Die Alten kannten ihre Mathematik, d.h. in diesem Fall die Triogonometrie, gut! Das Buch ist nicht leicht lesbar und in Seminaren haben Studierende der Mathematik zu Anfang wirklich Probleme, da sie viele der trigonometrischen Grundlagen gar nicht kennen. Aber die Mühe des Lesens lohnt sich. Ein großartiges Buch, bearbeitet von einem großartigen Editor.