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    Re: Slocum's lunars
    From: Steven Wepster
    Date: 2003 Dec 23, 16:47 +0100

    Hi all,
    
    Concerning the errors that Slocum would have discovered, let me add
    this.
    
    An article appeared in the 'Navigation'  journal (Vol. 44 no. 1, 1997)
    in which the author (S.Y. van der Werff) discusses lunar distances and
    particularly the lunar distance observation of Joshua Slocum on june
    16, 1896, shortly before his landfall on Nukahiva. He comes up with a
    completely different kind of error that Slocum discovered and
    corrected.
    
    Van der Werff notes that the Nautical Alamanc uses the astronomical
    date convention, i.e., a new day begins at noon, not at midnight. The
    layout of the lunar distance tables is such that one can not be
    mistaken by 12 hours, but not so the right ascension and declination
    tables. Van der Werff's suggestion is that Slocum accidentally took
    the RA/Dec values for a time 12 hours off (12 h too late, actually).
    Slocum's 'discovery', then, was that the tables were 12 hours off.
    
    If that was indeed the error that Slocum made, I conclude that he was
    _very_ unfamiliar with the time convention in the almanac. He would
    have had no earlier occasion to stumble over this difference of 12
    hours, or at least no such occasion had occured in the voyage with
    'Spray' and for quite some time before. It would imply that usually he
    took from the almanac only data that were forgiving of such an error:
    declinations, but no right ascensions. I would conclude that, on the
    large, Slocum's only means of astronomical navigation was by meridian
    altitudes.
    
    Does this appear as a likely scenario to list members?
    
    Steven.
    
    PS I will be away until after christmas.
    
    -----------------------------------------------------------
    Steven Wepster                          wepster{at}math.uu.nl
                                            tel +31 30 253 1531
    Mathematisch Instituut                      +31 61 251 4380
    Universiteit Utrecht
    PO Box 80.010
    3508 TA Utrecht
    The Netherlands
    ===========================================================
    
    
    

       
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