AAS 195th Meeting, January 2000
Session 130. HAD: The Papers of the Century
Special Session Oral, Saturday, January 15, 2000, 2:00-5:00pm, Regency V

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[130.06] Latitude for the Observer of Ptolemy's Catalog

B. E. Schaefer (Yale)

For centuries, researchers have claimed that substantial portions of Ptolemy's Almagest have been taken from Hipparchus in Rhodes (latitude 36.2 north). A substantial portion of these claims rest on the catalog of 1028 stars purported to be observed by Ptolemy in Alexandria (latitude 31.2 north). Various peculiarities is the star positions are inconclusive. However, aspects of the star catalog related to the visibility of stars near the horizon have not been treated with modern techniques. I have extensive experience in the heliacal rise, extinction angle, and the probability of detection (see Schaefer 1993, Vistas in Astronomy, 36, 311 for a review) all of which are critical to the problem. Also, I have been producing my own modern naked-eye star catalog so as to obtain practical knowledge of star visibility (especially near the southern horizon), completeness, and probability of detection. Also, I have determined the seasonal extinction coefficients (both median and best possible) for the eastern Mediterranean in ancient times based on 4000 in situ observations from 9 sites in modern and premodern times, measures of modern pollution components, and global models. Three criteria have been used to determine the latitude of the observer of the star catalog: First, the limiting magnitude (at the 50% level) as a function of declination can be compared against my model to derive the latitude. Second, the most southerly declination (at the 50% level) as a function of magnitude can also be compared against my model. For the first two criteria, quadrants are considered independently as well as individually to account for varying seasonal extinction and precession effects on the completeness of the traditional southern constellations. Third, the cataloged magnitudes are compared with modern magnitudes as a function of declination and compared with my extinction model for various latitudes.

The author(s) of this abstract have provided an email address for comments about the abstract: schaefer@grb2.physics.yale.edu

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