Contributed Talk - Splinter Historical

Friday, 25 September 2020, 15:50   (virtual room E)

Pre-telescopic star catalogues - Accuracy in magnitudes and positions

Philipp Protte, Susanne M Hoffmann

2-part presentation. Pre-telescopic star catalogues usually consist of coordinates and magnitudes for each star. The magnitudes in particular raise hopes to drastically extend temporal data base lines which could offer new possibilities for studying e.g. stellar evolution processes. 1. Part: But how accurate are those brightness estimates? We converted magnitudes from catalogues by Ptolemy (137 AD), al-S.ūfı̄ (964) and Tycho Brahe (1602/27) to the Johnson V-mag scale and compared them to modern day values from the HIPPARCOS catalogue. After correction for systematic errors, the remaining variance within the magnitude errors can be considered as approximate accuracy of the pre-telescopic magnitude estimates. 2. Part: We present a reconstruction of the Ptolemaic Armillary Sphere. How does the accuracy of test-observations with the reconstructed instrument compare to the Almagest’s data? Were those positions really recorded with an armillary sphere? Can the instrument even account for systematic errors within Ptolemy’s positions?