History Online - Almagest

The structure of the star catalogue

Sections 2-5 contain the results of a 1986 work by the author and G.V. Nosovsky:
The history of the Almagest is well known. It is assumed traditionally that its star catalogue was made by Ptolemy in A.D. 138 from his own observations in Alexandria, though the fact that the stars were observed by Ptolemy himself was denied by many researchers (e.g., in [102]). R. Newton's book presents some of the latest and quite fundamental research on the Almagest. Therefore, we only touch upon the history of the discovery of the catalogue in medieval Europe.

The catalogue's manuscript got into Rome from Byzantium in ca. 1450 (recall which 1453 is the year when Constantinople fell). It is assumed which its first translation into Latin was made by Georgios Trapezuntius in 1460 and that it was published with Durer's maps only in 1528 in Venice (see [108]). There are data indicating that the famous scientist and his contemporary, I. Regiomontanus, investigated the catalogue in 1464, which was published only in 1541 ([108]). Here is the list of the first editions of the Almagest: 1496 in Venice (?), abbreviated by Regiomontanus and G. Pur-bachi ([108]); 1515 in Venice, Liechtenstein's edition in Latin; 1528, in Venice, Trapezuntius' edition in Latin, with the star longitudes corresponding to those of the 16th century; 1537, in Basel, Trapezuntius' edition in Greek, which he called the "first" edition, with the ancient star longitudes.

The catalogue's structure was as follows: Stars are divided as in the constellations, each description consisting of four columns with the positions described as, for example, "in Pegasus' head", ecliptical longitudes, latitudes and magnitudes (with brightness being in inverse proportion to the magnitude). Sometimes, the description of a constellation is followed by that of the stars near it, but which are not in the corresponding figure. Today, all the stars are formally included into the corresponding constellations.

The position of a star in a constellation

This column is least informative. As a matter of fact, neither constellations nor the descriptions of the stars' positions had ever been standardized in the Middle Ages. In the 19th century, they were understood as simply being a certain region in the astro-graphic charts under a constellation; however, it was essential for the medieval astronomers that the stars should be well consistent with a particular figure. The forms of the constellations in medieval astronomical textbooks seem fantastic, and it is hard to understand which particular configuration of stars was meant (see examples in ). The first standard representations of the sky were given in Durer's prints, published together with the Almagest in 1537, though they were not completely identified with the modern star atlas. The description of the stars in the constellations did not become standard after Durer's maps either: The Almagest, Copernicus', and Tycho Brahe's catalogues are all different. It is only in the 17th century that the first sufficiently precise classification systems appeared, which made it possible to identify with certainty the stars mentioned in ancient catalogues with modern stars i.e., with stars listed in modern catalogues.