NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Working a lunar
From: George Huxtable
Date: 2007 Sep 20, 17:17 +0100
From: George Huxtable
Date: 2007 Sep 20, 17:17 +0100
Henry Halboth's latest message starts (and I've put his text within quote marks to distinguish it from mine)- "George and other doubters," and really, I must protest. We have seen many examples of Henry's precision in the past, and have no reason AT ALL to doubt his claims! "I'm sorry to say that my most recent Lunar effort came out to withing 4-minutes of Longitude on the first working. As I intimated in my post, this degree of accuracy is rather astounding and I am going over all my figures to search out any flukes before posting the numbers." Henry, don't apologise for something that anyone would be happy to achieve. It doesn't require a "fluke" to get such a spot-on answer. It doesn't imply that every such measurement, even those made by you, will show similar precision, though. The nature of such random scatter is that sometimes, any discrepancy will happen to be a small one. "George, you are well aware that this is not my first effort, as previous posts have spoken of much earlier efforts, before the publishing of distances, at least to my knowledge, and the advent of the internet, when I found it necessary to calculate the true distances for the time frames involved and based on almanac data available." What Henry says is quite true, that if you have to calculate lunar distances from positions calculated from almanac data for the two bodies, there are so many rounding errors in all the corrections that are involved, the accuracy gets seriously diluted. In the days when lunar distances were precalculated in the almanac, much of that dilution was avoided. "My real concern is, that should the accuracy attained in this latest effort be repeatable, then the Lunar Distance might well, as far as I am concerned at least, become a viable tool for use in emergency situations necessitating a recourse to celestial navigation in cases where accurate time be not available. This was my original intent in beginning work on Lunars in the 1940's and early 50's, but as, again to my state of knowledge at the time, there were no readily available tabulations of Lunar Distance against GMT, discontinued my efforts due to the amount of calculation necessary." Well, yes, but if it's going to be of use as an emergency tool, where are those precise lunar distance predictions going to come from? That was why I asked Henry for the source of the lunar distances he had used. And if it comes from some internet source, then I ask whether, at sea, in some undefined "emergency situation", such internet data is going to be available. If it's possible to print out in advance such predictions, and take them to sea, then that would indeed qualify as an "emergency tool" Or if Henry can take to sea some computing gadget that predicts such lunar distances on the spot from first principles, as is perfectly feasible, then lunars could be an emergency tool. But not, surely, if on-line web access is called for. Going back to the question of a single precise result, what I wanted to emphasise was that "one swallow doesn't make a Summer". I wasn't doubting any claim for consistency that Henry had made, because, indeed, he hasn't made any such claim, yet. I just wished to qualify any such claim, should one be in the offing. I doubt whether Henry, just because his recent lunar came out within 4 minutes, is going to claim that therefore 4-minute precision is achievable; my warning was made just in case he did. George. contact George Huxtable at george@huxtable.u-net.com or at +44 1865 820222 (from UK, 01865 820222) or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK. --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to NavList@fer3.com To , send email to NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---