NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Sunrise, Sunset, LAN, LMT
From: Henry Halboth
Date: 2004 Aug 4, 11:50 -0400
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 Boersmawrites: > 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 > > >