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    Re: Sunrise, Sunset, LAN, LMT
    From: Chuck Taylor
    Date: 2004 Aug 4, 21:17 -0700

    George Huxtable and Zorbec Legras pointed out that the
    method of finding longitude by equal altitudes before
    and after LAN is inexact.  I said as much, by
    describing it as falling into the category of
    "lifeboat navigation", by which I meant a method to be
    used when better methods are not available.  I also
    pointed out that it assumed minimal motion of the
    observer between observations.
    Despite the inexactness of the method, I find it
    interesting as an exercise in understanding the basic
    concepts involved.
    Best regards,
    Chuck Taylor
    North of Seattle
    --- George Huxtable  wrote:
    > Chuck Taylor wrote-
    > >In theory, if you had an accurate timepiece and
    > could
    > >observe the exact instant that the sun crosses your
    > >meridian (when it reaches its highest point), you
    > >could  then calculate your longitude by converting
    > >time to arc.
    > The exact instant at which the Sun crosses your
    > meridian is NOT the same as
    > the moment that it reaches its highest point.
    > There's a correction to be
    > made, to account for any North-South component of
    > the observer's speed, and
    > also to allow for changing declination of the Sun.
    > For the non-critical
    > timing of the moment to measure altitude (for
    > latitude), that correction is
    > unnecessary, but for any determination of longitude
    > it has to be included.
    > =================
    > Zorbec Legras wrote-
    > >Attention de greatest sun altitude is Not the
    > instant of transit for a
    > >mobile observer.
    > Nor is the instant of greatest Sun altitude (quite)
    > the same as the instant
    > of meridian transit, even for a stationary observer
    > (except at the
    > solstices), due to the changing declination of the
    > Sun. But it's close.
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