Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21712902b&link_type=abstract
American Astronomical Society, AAS Meeting #217, #129.02; Bulletin of the American Astronomical Society, Vol. 43, 2011
Astronomy and Astrophysics
Astronomy
Scientific paper
The Almagest (Book VII, Chapter 3: Toomer 1998) gives 54 stellar declinations attributed to Timocharis, Aristyllus, Hipparchus, and Ptolemy (“As found by us”). We evaluate these declinations (δ) by comparing them to precessed modern positions (d) obtained by using U.S. Naval Observatory software. A recent HIPPARCOS catalogue is the source of positions, proper motions, and parallaxes, and radial velocities come from the Yale Bright Star Catalog. The standard deviation (σ) is computed for Δ = δ-d for a plausible range of years for each observer. The minimum standard deviation, σmin , determines the accuracies and epochs of observation assuming that an observer’s observations were taken at approximately the same time. The results are: Timocharis, σmin = 0.135° and <Δ> = +0.022° at 295 BC: Aristyllus, σmin = 0.089° and <Δ> = -0.004° at 258 BC; Hipparchus, σmin = 0.113° and <Δ> = +0.010° at 128 BC; and Ptolemy, σmin = 0.199° and <Δ> = +0.005° at 115 AD. The precisions (σmin) are remarkable, the mean errors (<σ>) are small, and the dates are compatible with the historical evidence except for Ptolemy. The Δs for individual observers are approximately Gaussian except Timocharis’s value for Arcturus at 5.6σminwhich appears to be erroneous; our results are based on 53 declinations. The study of Almagest declinations by Maeyama (1984) uses the same approach and input data from the catalogue by Boss (1910). The results of the two studies are close, but with differences. Our values should be an improvement because of improved input data. We comment on the use of Almagest declinations by Tycho Brahe and Edmond Halley.
Brandt John C.
Jones Patricia B.
Zimmer Peter
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