NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: A basic sight reduction question
From: Stan K
Date: 2012 Apr 4, 16:33 -0400
From: Stan K
Date: 2012 Apr 4, 16:33 -0400
Greg,
The Bowditch wording is similar to the Nautical Almanac wording, implying that the v or d corrections should always be used, but this can result in a GHA or Dec that is 0.1' (possibly even 0.2') different than the hour value from the daily page for the whole hour case. This just goes against the grain.
My problem is more procedural than mathematical. What do I tell students to do when they are filling out a paper sight reduction form and the minute value is zero? One option is to always apply the corrections, which results in the "paradox". Another option would be to never apply them for 0 minutes, but then why are they even provided? A third option would be not to apply them for the whole hour case, but to apply them if there are any seconds. But why "any" seconds? Start at 15 seconds? 30 seconds?
I hope to eventually get some satisfactory weasel words from the UK Hydrographic Office.
Stan
The Bowditch wording is similar to the Nautical Almanac wording, implying that the v or d corrections should always be used, but this can result in a GHA or Dec that is 0.1' (possibly even 0.2') different than the hour value from the daily page for the whole hour case. This just goes against the grain.
My problem is more procedural than mathematical. What do I tell students to do when they are filling out a paper sight reduction form and the minute value is zero? One option is to always apply the corrections, which results in the "paradox". Another option would be to never apply them for 0 minutes, but then why are they even provided? A third option would be not to apply them for the whole hour case, but to apply them if there are any seconds. But why "any" seconds? Start at 15 seconds? 30 seconds?
I hope to eventually get some satisfactory weasel words from the UK Hydrographic Office.
Stan
-----Original Message-----
From: Greg Rudzinski <gregrudzinski@yahoo.com>
To: NavList <NavList@fer3.com>
Sent: Wed, Apr 4, 2012 4:04 pm
Subject: [NavList] Re: A basic sight reduction question
From: Greg Rudzinski <gregrudzinski@yahoo.com>
To: NavList <NavList@fer3.com>
Sent: Wed, Apr 4, 2012 4:04 pm
Subject: [NavList] Re: A basic sight reduction question
Stan,
See img 3179 for the 1984 Bowditch explanation. When looking at the interolation tables for v and d as seen in img 3178 it can be seen that a correction of 0.1' for a d value of 1.0' shows up at 3 minutes time. The precise correction at 3 minutes time is 180s/3600s = .05' moa
Greg Rudzinski
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