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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Star-star distances for arc error
From: George Huxtable
Date: 2009 Jun 28, 08:52 +0100
From: George Huxtable
Date: 2009 Jun 28, 08:52 +0100
I had pointed out defects in Appendix G of John Karl's book, which affected the accuracy of its results to a user. Frank pooh-poohed these, writing- "But calling them "serious weaknesses" when there are simple solutions strikes me as a bit of an exaggeration.", adding "... it would take no more than an index card sized "errata" sheet to cover those particular items". Yes, of course, it would have been easy to put them right, if they had been anticipated. But, as there was no such errata sheet supplied with my copy (was there, with others?) there was no way a reader could avoid being misled. So: in what way does the potential ease of fixing those problems make them less serious as weaknesses, for the reader? As for Problem #2:, I had written- "No account has been taken of annual aberration, which varies cyclically over the year, and in the worst case can amount to errors in star-star angle amounting to 40 arc-seconds". And Frank responded- "OK, but the error should be no more than 20 arcseconds if the mean distance has been used (I haven't checked to see whether he did that or not). " He hadn't checked that, but I had. The mean distance hadn't been used. The distances were all based on a spot-value, at one arbitrary time-of-year. The possible error that I gave had been correctly assessed. So on what basis did Frank consider himself entitled to halve that number, without even bothering to check? This attention being given to appendix G distracts from the real value of John Karl's book, and I understand that in the new edition, this, and a few other matters, are corrected. 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. --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---