NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Longitude around noon (a twist)
From: Frank Reed
Date: 2008 Jun 03, 11:42 -0400
From: Frank Reed
Date: 2008 Jun 03, 11:42 -0400
I made one last try at convincing George Kaplan (a name some of you know) to join us in Mystic this week, but alas, it's not in the cards. While I was at it, I chatted in my email a bit about longitude around noon and asked him this: "Which leads to a question: is there an established name in the literature, or even in your own jargon, for a fix resulting from a series of ten or twelve sights taken over a relatively short period of time? I've been calling it a "rapid-fire fix". Do you know another name?" His reply: "I don't know of a special name. You're correct, of course, if you can get a bunch of sights on either side of noon, you can get good enough geometry to get a 2-D position. It works with the LOPs, too, in that they provide a good spread of azimuth around then. There is a slight catch, however, and that is, the higher the Sun is in the sky (and therefore the more rapid the altitude and azimuth change near noon) the more you have to worry about the curvature of the LOPs. In some near-degenerate cases (sun within several degrees of the zenith), the usual straight-line plotting -- or math that assumes straight-line LOPs -- may not provide the right fix." That's a good point about sights very close to the zenith. I had mentioned previously on the list that there may be a special case when the Sun is close to the zenith. I still haven't thought through whether it really screws up the graphical technique or merely requires more stringent rules for its application. -FER --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---