As some of you know I have written many ephemeris programs and the like over the last 52 years, and in the course of doing so I have worked with a good many observational astronomers. They often, indeed routinely, use the term precession to mean discrepancy between observation and a calendrical model.
Many things affect the rotation of the earth on its axis and its revolution about the sun. On certain heroic assumptions one can calculate the individual values of these second-order effects---the relative positions of the other planets are, for example, important. This is worth doing, but the the contrarian view that lumps all discrepancies between observation and model together is sometimes convenient too. What needs to be remembered is that none of these problems is tractable mathematically. We can treat special cases of the three-body problem, but the n-body problem has so far eluded us completely. Statistical methods, particularly ANOVA, are currently unavoidable. The extra days in leap years do of course help to preserve seasonal alignment, but they do so very imperfectly, and terminology that omits to recognize this is problematic. Shmuel is apparently confident that he knows more about these matters than I do, and I am entirely comfortable with that, as I am with his view that he knows more English grammar than I do. There are already a number of "simpler and more accurate" leap-year schemes in use. In particular the modern version of the Persian Djalali calendar, created originally by a committee chaired by Omar Khayyam (1048-1131), which is used in Iran and (with different month names) Afghanistan is very much more accurate. I shall have nothing further to say about this topic. John Gilmore, Ashland, MA 01721 - USA ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
