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    Re: Jack Aubrey's fixing of longitude
    From: Hanno Ix
    Date: 2011 Jun 23, 11:26 -0700
    May I add a remark to this issue?

    One can determine longitude by the time difference of the meridian passages of sun and moon at one's - unknown - position.

    If you are on land, no matter how small, you can accomplish this even with a pendulum clock of stopwatch quality and a sextant. Naturally, you also need an accurate almanac. I estimate the accuracy of the method equal to that of lunar distances in general.

    So, this could have been accomplished at Capt. Cook's times. Of course, it cannot be done shipboard but the method could have been used to reset a run-down chronometer during a visit to a port, for instance.


    From: Hewitt Schlereth <hhew36---.com>
    To: NavList@fer3.com
    Sent: Wednesday, June 22, 2011 7:37 AM
    Subject: [NavList] Re: Jack Aubrey's fixing of longitude

    Well, gee, if I misconstrued Albert, I apologize. But he wrote "Lunars can be ruled out as the necessary data was not available at the time. Regarding the lunar occultation, why should he rely on such a seldom event?"

    So, first he made a comment about non-availability of date for lunars. Then he switched to a comment about occultations.

    Seemed to me he was saying Jack wouldn't try to determine the longitude by a lunar because the data wasn't available.

    As to why Jack would be using another technique, I'd guess it was part of his ongoing interest in determining longitude by astronomy. Recall his struggles to make shipboard observations of occulations of the moons of Jupiter - Jack hanging in a sling and crew attempting to hold him steady.

    Anyway, my apologies again to Albert if I mistook his meaning. I do think his suggestion that Jack was trying for a very accurate bearing of moon/venus set makes sense..

    Hewitt



    On Wed, Jun 22, 2011 at 10:06 AM, Dave Walden <waldendand---.com> wrote:
    There is a difference between "data not available" and "lunar distances included in NA". Calculating the required lunar distances is MUCH easier than carrying out an occultation calculation.

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