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How many of you critics have actually tried to obtain Longitude by equal
altitudes. As is the case with almost all methods of navigation there are
limitations to its use, however, at the right time and place it can be
useful, and was considered important enough to navigators of yesteryear
to be included on Steamboat Inspectors license examinations. By actual
practice, I have found it to be quite a useful tool. Any text old enough
to include Lunars, generally includes a section or sections on both
Longitude and chronometer error by equal altitudes. I recently posted an
example of Latitude + Longitude at noon to which I would refer you and
solicit comments. Since the advent of electronics, it has been customary
for navigational texts to denigrate celestial navigation, and I cite this
as another example based on simple inexperience - when one discusses
position finding to a matter of feet, all celestial navigation can be
accounted an approximation and probably someday will be.

On Wed, 4 Aug 2004 21:17:03 -0700 Chuck Taylor 
writes:
> 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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