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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Multi-Moon line exercise in 2 parts
From: George Huxtable
Date: 2009 Aug 8, 14:36 +0100
From: George Huxtable
Date: 2009 Aug 8, 14:36 +0100
Peter Hakel (PH) wrote, in [9409], about Jeremy's closely-spaced sequences of Moon altitudes, in [9359]- "An important detail is that I obtained this result by disregarding the second measurement (at 8:54:46) because its intercept does not seem to "belong" among all the others (it is AWAY, while all others are TOWARD). If I do include this outlier, the results get worse:" Yes. A simple plot of Jermy's data "Moonlines, Moon away from LAM" shows that the observation at 8.54.56 is a real misfit, and should be discarded. It seems most likely that there was a recording or transcribing error, and that it should have been noted as 8.52.56, but it's not safe to guess at such things, and the only safe procedure is to delete that line. Peter did the right thing. What, by the way, do the letters LAM stand for? With that line deleted, those two data sets show remarkably little scatter. A least-squares fit to the non-culminating series arrives at a rms scatter of little more that 0.1 arc-minute, and of the series around culmination of about 0.15 arc-min. These show only random errors, not systematic ones such as those due to index error observation or dip; they show what can be achieved by a careful observer on a large vessel in, presumably, benign conditions. George. contact George Huxtable, at george@hux.me.uk or at +44 1865 820222 (from UK, 01865 820222) or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK. --~--~---------~--~----~------------~-------~--~----~ NavList message boards: www.fer3.com/arc Or post by email to: NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---