41

41 See [173

Ptolemy Almagest After Durer
Figure 1.18: An astronomical chart by A. Durer that was published in the first edition of the Almagest

the latitudes, leading to a suspicion that they were obtained by a method quite usual in the Middle Ages: by measuring equatorial coordinates and subsequently recalculating them into ecliptical ones. Since the calculations of the ecliptic longitudes were much more complicated, larger errors arose and the accuracy failed, making them useless for the purpose of dating the Almagest. In addition, the longitudinal precessions were already well known in the Middle Ages, what could have been tempting to manipulate this data. The method used in [101] was applied to latitudes only. Its effectiveness was tested on the several star catalogues whose dates are well known (for example the star catalogue of Tycho Brahe, Bonner Durchmusterung, etc.). It involved extensive computations which were done using specially writhen for this purpose computer programs.

Writhen Pictures

Figure 1.19: An astronomical chart by A. Durer that was published in the first edition of the Almagest i 1 ¿bula

Figure 1.19: An astronomical chart by A. Durer that was published in the first edition of the Almagest

For the purpose of computations, a list of 80 relatively fast moving stars was compiled, using the modern star catalogue by D. Hofflit (The Bright Star Catalogue). Based on this list about 35 stars were identified in the Almagest, from which three had to be rejected because their identity couldn't be indisputably established. Let us point out that it was not a trivial question to identify some of the stars in the Almagest. Basically, the star identifications in [101] confirm those made by F. Peters and E. Knobel. The idea was to consider, instead of individual stars, the whole collection of the moving stars in order to calculate the date when they were observed on the sky. In this approach the whole collection was considered as a single body moving on the celestial sphere. Let us mention, without entering into the mathematical formalism behind this computations, that the obtained in [101] results do not confirm the traditional date of the Almagest but shift its dating to the epoch from 600 to 1300 A.D. — the confidence interval corresponding to probability p = 99.8%

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