NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
The Noon Fix
From: John Karl
Date: 2009 Apr 12, 08:10 -0700
From: John Karl
Date: 2009 Apr 12, 08:10 -0700
Jim, now I'm a believer. I've taken the exact data from my previous post and applied your correction ( Hstationary = Hmoving + Sn*T) to bring the H-Time plot from a moving vessel (at 10 knts northerly) to what would be observed by a stationary observer. The result is excellent, with the max error from the exact value generally less that 0.1'. I had to prove for myself (and hopefully for others) that your simple linear approximation is valid for the highly nonlinear Sin(H) altitude equation. That was far from obvious to me. Congratulations on your intuition! George, I don't understand your point. The curves of my previous plot are data that would be observed from separate vessels traveling north at speeds from zero to 10 knts. All five vessels are at the same latitude (N69) at T = 0. The plotted times are thus relative to this T=0 time and therefore show the relative time shifts of LAN from the five different ships, this is what we're discussing -- it's just what we want. BTW, I made no correction for changing declination for two reasons. The max rate 1'/hour is small, plus the altitude equation is symmetric in Dec and Lat so the effect is the same for each (as Jim has in his discussion). Sorry for starting a new "thread" (as I think it's called). But I can't figure out how to make an attachment directly at the NavList site. --John --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---