The Measurement Method of the Almagest Stars

I suggest that the correct standard model of early Greek stellar astronomy is A. Someone, perhaps Hipparchus, measured a fairly complete star catalog in equatorial coordinates. B. That catalog was the basis for the results presented in Hipparchus ’ Commentary to Aratus.1 C. Analog computation was used to convert most of the catalog to ecliptical coordinates. D. It is this converted catalog, with longitudes shifted by 2°40´, that we have received through Ptolemy and the Almagest. The supporting argument in brief is: The star coordinates in Hipparchus ’ Commentary to Aratus are clearly equatorial right ascensions and declinations.2 Although we have no surviving hint how those coordinates were measured, or even who measured them, it is reasonable to assume that the coordinates were measured in the same way they were presented: equatorial coordinates. Ecliptical stellar coordinates are conspicuous in their absence. The correlations between the errors in the Almagest data and the Commentary data show that those two data sets are associated in some way. This is substantiated by3 (a) several stars with large common errors in each data set, (b) detailed statistical analysis of the error correlations between the two sets of data, and (c) similar systematic errors in the two data sets. These facts are most easily reconciled by assuming a catalog in equatorial coordinates that was used to calculate the Commentary data, and was eventually used in substantia