Welcome to the NavList Message Boards.


A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

Compose Your Message

Add Images & Files
    Re: Slocum's lunars
    From: Herbert Prinz
    Date: 2003 Dec 23, 13:06 -0500

    Hello Steven,
    I have read this article, but I don't think the author makes his case. Van
    der Werf only speculates that the time argument might have been the
    problem, because he does not find any other discrepancy in the almanac.
    However, he does not show in detail how exactly the wrong longitude could
    have come about.
    If we accept the theory, we must twist a lot of words in Slocum's text:
    1. Slocum does not say that he found an error in the Almanac, he says he
    found it in the "tables".
    2. Slocum says that a "logarithm" was wrong. RA and Dec are not tabulated
    as logarithms.
    3. Slocum says a "column" was in error, not the whole almanac.
    Furthermore, RA and Dec don't enter the distance computation, unless the
    altitudes are computed (and if so, as with some precise methods, only as a
    small correction). So the error could only have affected the reduction of
    the time sight that was taken in connection with it. May we really assume
    that Slocum did not know how to do a time sight? When he re-took the
    observation an hour later, he would have taken the distance and altitudes
    again. But for both reductions he would have used local apparent time as
    obtained from an earlier observation for time, wouldn't he? Of course, he
    could have established LAT simultaneously with distance from Moon and Sun.
    But this was not easy and certainly not common practice.
    And finally, a twelve hour shift of the time argument can affect
    declination of the sun by up to 12' around equinox. If we grant Slocum
    that he performed at least noon sights regularly, this puts his various
    claims about the accuracy of his navigation to within a few miles in an
    interesting light.
    In short, the problem that I have with van der Werf's explanation is that
    we can accept it only if we assume that Slocum did not know what the hell
    he was doing.
    Steven Wepster wrote:
    > Hi all,
    > 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'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.

    Browse Files

    Drop Files


    What is NavList?

    Join NavList

    (please, no nicknames or handles)
    Do you want to receive all group messages by email?
    Yes No

    You can also join by posting. Your first on-topic post automatically makes you a member.

    Posting Code

    Enter the email address associated with your NavList messages. Your posting code will be emailed to you immediately.

    Email Settings

    Posting Code:

    Custom Index

    Start date: (yyyymm dd)
    End date: (yyyymm dd)

    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site