Next message: Noyce, Bill: "Re: Sunrise, Sunset, LAN, LMT"
You are quite correct, except that the accuracy of Longitude increases
materially as the Sun's position approaches the prime vertical, i.e., a
large error in Latitude does not affect the Longitude as greatly if the
Sun is in the Prime vertical.
On Wed, 4 Aug 2004 00:21:41 -0400 Mike Boersma <>
writes:
> You could try a time sight. If you have very accurate latitude, the
> altitude of the sun and the declination of the sun, you can solve
> for
> the meridian angle, which is then converted into LHA. The difference
> between GHA and LHA is the longitude. Longitude = time. See table 20
> in
> the online Bowditch. This method is VERY prone to error due to
> latitude
> errors. Small errors in latitude lead to large errors in longitude.
>
> Meridian angle = t; h = altitude; d = declination; L = Latitude:
> cos t
> = (sin h - sin L*sin d) / cos L * cos d
>
> Z = sin t * cos d * sec h
>
> t = LHA. GHA - LHA = longitude.
>
> A less error prone method, and perhaps the preferred for determining
> GMT
> in the circumstances that you describe, is by means of lunar
> distance.
>
> Good luck,
>
> Mike Boersma
>
> Andrew Corl wrote:
>
> > I am slowly teaching my self celestial navigation. I have a copy
> of
> > Dutton, which many of you on this list recommended to me, and a
> > downloaded copy of Bowditch. I am working my way through noon
> sight
> > and grasping the concepts, the online almanacs I am finding to be
> > pretty good and easy to understand.
> >
> > Now I come to my problem. I downloaded a problem from the website
> > www.oceannavigator.com entitled "Navigating without a clock."
> This
> > problem deals with a noon sight to determine latitude but there is
> no
> > clock on the ship. Lest anyone get to worried, the author of the
> > problem does make several assumptions to make the problem
> solvable.
> >
> > I have looked in a number of places for a paper and pencil method
> to
> > determine GMT as well as sunrise and sunset. I have found a basic
> > computer program from Sky and Telescope magazine in 1994 which
> shows
> > how to determine sunrise and sunset at a selected position, but so
> far
> > no way to determine noon GMT. I know that this information is
> > provided in the nautical almanacs on the daily pages, but I am
> looking
> > for a way to calculate this number using a pencil and paper. I
> have a
> > pretty good feeling this is going to be somewhat difficult, but I
> am
> > willing to make the attempt. I know that there are spreadsheets,
> and
> > computer programs capable of doing this, but I am looking for
> pencil
> > and paper
> >
> > If anyone can direct me to a reference or a guide either online or
> in
> > print I would greatly appreciate it.
> >
> > I will keep plugging away at this. Thanks for all your help.
> >
> > Andrew
> >
>
