NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Lunars Tables
From: Fred Hebard
Date: 2007 Dec 2, 20:12 -0500
From: Fred Hebard
Date: 2007 Dec 2, 20:12 -0500
I don't know where Bruce is. He was never in the best of health while posting here. Bruce's math has been posted on the list piecemeal. It's possible that Frank Reed summarized it in one posting. Bruce's method is a direct solution of the clearing problem, rather than a solution involving approximations, such as that published by Bowditch. I believe the approximation methods may be quicker than Bruce's method, at least for hand calculations, but perhaps not by much. Both go pretty instantaneously on modern computers. Bruce came up with an ingenious and novel method for accomplishing a subtraction between two trignonometric quantities without having to transform from logs to antilogs, and then back. That must make his method the shortest of the direct-solution methods using tables and pencil and paper. The advantage of Bruce's method is that it is available in one book, today, whereas tables for the approximation methods are out of print. I don't know that anybody uses lunars for actual navigation, with accurate Greenwich time so readily available. Those who have used them to calibrate sextants have usually used Frank Reed's online lunar clearing calculator, or perhaps computer programs of their own that solve the clearing equations directly. Here, the focus is on calibrating the sextant, not practicing clearing by hand. If you were planning to go to sea and rely upon lunars as a backup or primary means of finding longitude, you would want to practice with Bruce's tables extensively, until their use became second nature. Likewise, for standard sight-reduction tables. Fred On Nov 30, 2007, at 6:45 PM, Scott Owen wrote: > > Bought a copy of Bruce Starks, Tables for Clearing the Lunar > Distance a > few weeks ago. From the archives it looks as though Bruce was a > regular > contributor but I did not see anything of late. I have two questions: > > 1) Are these the tables most members use for reducing Lunar > observations or is there some other preferred method/tables? [I know > there are many methods to do this, I'm just trying to get a feel for > what method list members are using and what may be considered the most > accurate method.] > > 2) Is anyone familiar with the trig/math that Bruce used to derive > his > lunar tables? If so, does anyone know if Bruce is amenable to posting > it on the list or has it been posted in the past and I just missed > it in > the archives? > > Thanks in advance. > > --Scott > > > --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to NavList@fer3.com To , send email to NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---