NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: sight reduction tables
From: George Huxtable
Date: 2007 Sep 30, 00:54 +0100
From: George Huxtable
Date: 2007 Sep 30, 00:54 +0100
It was quite a pleasure to read posting [NavList 3296] by Gary LaPook, in favour of the HO249 tables. Well-informed, and well-argued, it was highly convincing. As I have stated before, I've no experience of using either HO229 or HO249, so have no intention of taking sides in any such debate. Indeed, I have argued over several years, on this list and others, that navigating by altitude sights from a small craft, in anything but the calmest weather, is an inaccurate business, with likely errors of a few arc-minutes. So I fully agree that for such a purpose, there's no need for sight reduction tables to be precise to 0.1 arc-minutes, and the precision of HO249, to no better than a whole minute, is entirely appropriate. I hasten to add that for observations taken from a big ship, or from on land, the higher precision of other tables might well be useful. And yet there's a bit of a contradiction here, it seems to me, in the attitude of many small-boat navigators; those who prize their expensive sextants, reading to 0.1 arc-minutes, and wouldn't be seen dead using a plastic sextant, no matter how good it may happen to be. I raise this matter at the risk of reopening old wounds here, but it would seem to me that if HO249 is acceptably accurate, then so too would be a decent plastic sextant. I'm not arguing against Gary here; I simply don't know whether he is a member of the diehard posh-sextant brigade or not. But they exist, and for them, would the 1-minute precision of HO249 be considered good enough? I would agree, however, that for those who wish to measure lunar distances, for which high precision is necessary, and (because no horizon is involved) possible, there's really no alternative to a metal sextant of the highest quality. 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 -~----------~----~----~----~------~----~------~--~---