NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Rejecting outliers
From: Gary LaPook
Date: 2011 Jan 8, 17:48 -0800
From: Gary LaPook
Date: 2011 Jan 8, 17:48 -0800
| Examining the MOB table again reveals that for latitudes of 20° or less the worst case is 0.4' altitude change per minute for a 5° change in latitude; 45° or less, 0.9' and for 60° or less, 1.1' for a 5° change in latitude. It is hard to believe your DR latitude would ever be off by 5°, 300 nm. As to change of rate due to change in azimuth, it changes in the opposite sense with latitude, becoming smaller with increases in latitude. Worst case at 20° or less latitude is 0.5' for a 2° change in azimuth; 45° latitude, 0.4'; 60° latitude, 0.3' per 2° change in azimuth. At 60° latitude the azimuth will change 2° in 4 minutes for declinations of 29° or less and 3° for declinations up to 45° (there are only 10 listed stars with declinations greater that 29° north) so even at that latitude, a 30 nm error in longitude would result in less than a 2' difference (for most stars) in the altitude computed with the MOB table (resulting in a 2' error in the graph of the slope) in a four minute period so this method should be usable even at high latitudes. As for difficulty in actually measuring the azimuth, if you pre-compute the data for presetting the sextant then you will have the azimuth to use in computing the slope with the MOB and MOO tables. gl --- On Sat, 1/8/11, George Huxtable <george@hux.me.uk> wrote:
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