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    Re: Sunrise, Sunset, LAN, LMT
    From: Henry Halboth
    Date: 2004 Aug 4, 11:50 -0400

    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
    > >
    >
    
    
    

       
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