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From: Mike Boersma (no email)
Date: Wed Aug 04 2004 - 00:21:41 EDT
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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