Almagest Declinations: Ptolemy or “As found by us”
Abstract
Consistent results and compatibility with historical evidence were reported by Zimmer, Brandt, and Jones for Almagest declinations determined by Timocharis, Aristyllus, and Hipparcus. Unfortunately, this situation does not apply to the Almagest declinations (Book VII, Chapter 3; Toomer 1998) for Ptolemy or “As found by us.” Our formal solution gives a precision of 11.9 arc min and an epoch near 115AD. The precision is significantly worse than for the earlier observers and the date conflicts with historical data. Inspection of the (O) - (C) plots vs. year reveals that the natural clustering of trajectories seen for the other observers is not seen for the Ptolemy declinations. In addition, the spread in dates of observations estimated from the times of (O) - (C) = 0 shows a much larger value for Ptolemy than for the others. Historically, the Almagest was published around 150AD or perhaps a little later. Ptolemy’s life span was likely from c.100AD to c.175AD. Thus, the 115AD date for his observations is much too early. Maeyama (1984) moved the epoch from 115AD to 137/138AD by dropping stars from the analysis. Rawlins (manuscript, c. 1983) has an extensive discussion, drops several stars, and finds a preferred epoch of 137AD. He regards the observer as unknown. We prefer not to drop stars from the analysis unless the evidence is overwhelming. Our solution is to take Ptolemy literally. In Toomer (1998; tables on pages 331 & 332), these declinations are “As found by us” and in Taliaferro (1952; in the text) are as “we find it.” The idea of multiple observers has been suggested before and our analysis certainly supports the declinations coming from multiple observers through the years.
- Publication:
-
American Astronomical Society Meeting Abstracts #221
- Pub Date:
- January 2013
- Bibcode:
- 2013AAS...22120801B