History Online - Chronology

In my opinion, all these remarks made in are very subjective and can be interpreted in different ways. We need some strong statistical method for dating the star catalogue. The difference between the Latin and Greek editions of the Almagest (see items 4 and 5) shows that we need to base our research on the ancient manuscripts of the Almagest. We base our work on the "canonical" version of the Almagest's star catalogue as presented in the fundamental work of Peters and Knobel (Ptolemy's Catalogue of Stars. A revision of the Almagest, Carnegie Institute, Washington, 1915). They investigated all the main manuscripts of the star catalogue.

The attempts to date the catalogue on the basis of the displacement of individual stars such as Arcturus are not convincing. This motion is extremely slow, only several seconds a year. Recall that the astronomer Halley, on the contrary, calculated the value of Arcturus' proper motion, referring to star longitudes and the traditional dating of the Almagest to the 2nd century A.D. In reality, the values of the proper star displacements are small and of the order of the measuring errors; therefore, to date the catalogue reliably on the basis of individual displacements is complicated. (See details in the next section.)

Dating catalogues by the deviation from modern star coordinates should be generally very accurate. For example, it is on the basis of a ca. 20° difference between the longitudes in the Greek and the Latin editions that traditional chronology makes a conclusion about their having been observed in the 2nd century A.D. It is tacitly assumed, however, that both the ancient and medieval astronomers counted longitudes from the same "basic point". To give just one example, the famous Theatrum Cometicvm by the 17th-century author Stanislaw Lubieniecki should be "dated" to the 5th century B.C.! This absurd conclusion is due to Lubieniecki's having counted the longitudes off the first stars of Taurus, which led to a large difference with the modern longitudes, and which is not accepted today. There are very many similar examples . Methods of the computation of longitudes simply were diverse in the Middle Ages, and each author took different stars as initial reference points, resulting, in a difference in the longitudes, and therefore not at all explained by precession.