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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: It Works.
From: Arthur Pearson
Date: 2002 Apr 8, 17:41 -0400
From: Arthur Pearson
Date: 2002 Apr 8, 17:41 -0400
Bruce et. al. Our digression into SHA meridian was not time wasted; I have finally grasped the concept. Although we may conclude that given Bill Noyce's insight, the method is unnecessary, I think it is remarkably elegant solution. As I now understand it, LAN is essentially used as a way to mark our place on the SHA scale without regard to exact time or longitude. The SHA Sun simply does not vary much over an hour (about 3.4' in the hour I looked at), so this is pretty accurate even without exact time. Convert to arc the time from LAN to the lunar to we can get SHA meridian at the time of observation within +- 3' roughly. That's pretty good for a vessel with a chronometer that may be out by 30 minutes or more. It is as if one re-set the "SHA Clock" each day using LAN. A very elegant derivation, I can't help but think there are other uses for the principle. That said, I am relieved by Bill's insight that if we are using celestial fixes to begin with, the error in time and longitude will cancel out. It eliminates the need for special procedures in anticipation of a lunar. I need to work out the example to make sure I understand it, but it does feel we have come full circle. Regards, Arthur -----Original Message----- From: Navigation Mailing List [mailto:NAVIGATION-L@LISTSERV.WEBKAHUNA.COM] On Behalf Of Bruce Stark Sent: Monday, April 08, 2002 2:42 PM To: NAVIGATION-L@LISTSERV.WEBKAHUNA.COM Subject: Re: It Works. Like George, I've been "Off watch." But for longer time and for less interesting reasons, one of them being that a backhoe took out our telephone line. A lot of good postings. William Noyce's insight, that the problem we were discussing on the "It Works" thread takes care of itself, is beautiful. Why didn't we see that?! I'm sorry now I posted that method of finding SHA meridian, etc. It injects the old nautical astronomer's way of thinking into the discussion. It isn't needed, and confuses the issue. Arthur and others should forget about SHA meridian and put to practice what William has said. That way they will see how it works and develop confidence. Don't think I have anything to add to what George has said. Glad he pointed out that noon is the worst time to get local time. Hope the "Artificial Horizon" thread will remain as lively. Bruce
