NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: George, is there a Part 4c?
From: George Huxtable
Date: 2004 Sep 25, 00:15 +0100
From: George Huxtable
Date: 2004 Sep 25, 00:15 +0100
Jim Thompson asked- >Was there a Part 4c to your very useful Part 4b >http://members.verizon.net/~vze3nfrm/LunarsFiles/Lunarsp4b.htm? ================= Jim refers to a series of long-ago Nav-L postings, which, with posting dates, were About Lunars, part 1, 29 Jan.02 About Lunars, part 2, 29 Jan 02 About Lunars, part 3, 12 Feb 02 About Lunars, part 4b, 24 Jan 04 Perhaps these are still there in the archives if anyone wishes to go digging. Jim asks about an issue 4c. The curious numbering of the parts came about because quite a lot of updating took place on part 4, mainly putting matters right when discussion on this list unearthed errors. So there existed first a part 4 and then a part 4a, but these should now be discarded, having been supplanted by 4b, the current version. What I think Jim is looking for is not 4c, but part 5, and maybe part 6. The present series ends (at 4b) with the navigator finding his Greenwich Time from a lunar. What remains to be written is a final part (or parts) showing how he can make observations for Local Apparent Time (at the ship) and then derive his longitude from the difference between these times. Finalising this series has become something of a family joke in the Huxtable household. I have promised to do so to myself and also to Nav-L members, and have started to write part 5, several times now! Let me explain the difficulties I have met. Nav-L members who follow lunar distances have a range of interests. Some want to measure lunars "as of today" from their boat or backyard, some with recently computed tables and a modern almanac, some in which a computer or pocket calculator does all the work. Some wish to follow old voyages or land-journeys, from old logs and journals, in which inland navigators would reflect their altitudes in an artificial horizon. Some are interested in using the same old log-trig functions and methods that were required of early navigators, others not. Over the years there has been a series of changes, particularly to the nautical almanac. It changed its time-scale from apparent to mean time, it introduced lunar distances for planets, later Greenwich Hour Angle took the place of Right Ascension. Methods for clearing the lunar distance developed throughout the lunar era (of say 1760 to 1860). Where I have found the greatest difficulty is in covering all these different aspects when explaining how to find a lunar longitude, without adding a great mass of inclusions and exceptions which would bog the reader down. I haven't given up, yet. So that series "About lunars" may be completed, with a part 5 and perhaps a part 6, but I have given over promising when. If any Nav-L members are keen on picking up the existing four parts of "About lunars" without delving into the archives, then on request I will repost those four (longish) messages. Yours, George. ================================================================ contact George Huxtable by email at george@huxtable.u-net.com, by phone at 01865 820222 (from outside UK, +44 1865 820222), or by mail at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK. ================================================================