AD 150

Almagest

Ptolemy publishes the Almagest, approximately

The best evidence against a 140 completion is Ptolemy's own stone inscription: put up in 146/147, it still carries models he later corrected.

The stone that rules out 140

Ptolemy's dated Canobic Inscription of 146/147 preserves an earlier version of several astronomical parameters that he corrected in the Almagest. The received text therefore cannot have been finished in 140.

About 150 CE is a scholarly reconstruction, not a record. No surviving evidence identifies a completion day, or even a securely established year.

Thirteen books of models and tables

Claudius Ptolemy, working at Alexandria in Roman Egypt, produced a systematic thirteen-book textbook of mathematical astronomy.

It supplied mathematical models and tables for calculating the positions of the Sun, the Moon, the five known planets and the fixed stars. Ptolemy had dated the Canobic Inscription by the tenth regnal year of Antoninus Pius, then revised those constants for the book.

It is principally a mathematical and computational treatise. Ptolemy developed more explicitly physical celestial constructions later, in the Planetary Hypotheses.

1,022 stars in 1,028 entries

The star catalogue runs to 1,028 entries covering 1,022 stars — the two numbers are not interchangeable.

How much of it came from Hipparchus is still argued. Scholarship supports the incorporation of Hipparchan material, but the extent and the catalogue's precise construction remain open questions.

Nor was the book called the Almagest when Ptolemy finished it. That name came later through Arabic transmission; his own title was Mathēmatikē Syntaxis.

Sources

Researched 23 Aug 2026 6 sources not yet audited Date disputed

How this was checked

Researched from the web into a fact sheet and rewritten from that sheet. This article has not yet had an independent model audit. How the pipeline works →

Date disputed. Sources disagree; the research places it at ~0150.

What the sources leave uncertain

The listed year 140 is not supported by the strongest dating evidence.
The work contains layers compiled over time, and the surviving text has no dated publication notice or authorial colophon.
Circa 150 is an inferred publication date: the 146/147 Canobic Inscription demonstrably represents an earlier stage of Ptolemy's models.
The title Almagest is later, deriving through Arabic; Ptolemy's title was Mathēmatikē Syntaxis.