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    Re: Long Term almanac
    From: Steven Wepster
    Date: 2004 Mar 31, 18:51 +0200

    Mike,
    
    I checked my 1981 edition of Vol.II and it too is based on 1972. According to
    the description errors should not exceed 2'.0 for the sun or 1'.3 for stars.
    It does not explicitly give a period within which these error bounds are
    believed to be correct. But it has an example for July 18, 2002 which implies
    that 2002 is supposed to lie inside that period.
    A quick check against XEphem shows that both GHA and Dec differ less than half
    a minute for that date.
    I also noticed that the D column in the multiplication table has entries up to
    argument 54, which suggests a valid time of at least 4x54 = 216 years from the
    epoch 1972.
    The tables allow for precession but not for nutation, since the basic period
    of nutation is 18 years and there is no way to incorporate an 18-year cycle in
    these tables. They can only represent linear terms and terms with a period of
    4 years. Proper motion of the stars is provided for, and I suppose that
    secular (or very long periodic) terms have been swallowed in the linear terms.
    I might be off on this, though.
    As a backup, I think, these tables would suffice for quite some time to come,
    within the error limits stated. You could check it against some trustworthy
    ephemeris software.
    
    Steven.
    
    
    

       
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