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Re: Latitude by Noon Sun for Beginners
From: Jean-Philippe Planas
Date: 2009 Apr 29, 14:20 -0700
Note that on this day, at 12h00, the sun GHA is 356° 56.9', not 360°. Therefore that day LAN occurs at Greenwich at 12h 12m 12s.
JPP

--- On Wed, 4/29/09, JKP{at}obec.com <JKP{at}obec.com> wrote:
From: JKP{at}obec.com <JKP{at}obec.com>
Subject: [NavList 8103] Re: Latitude by Noon Sun for Beginners
To: NavList@fer3.com
Date: Wednesday, April 29, 2009, 3:19 PM

```Gary,Thanks very much for your in-depth explanation. I find that it was thedeclination giving me trouble, and I finally realized I was subtractng 30'for the "d" correction, not 0.5' as I should have. (Half a degereeinstead of half a minute!) So for the time of the sight I (eventually) got adeclination of 18d
59.8'S and the correct latitude of 55d 37.8'S.  Whew!As an aside, you asked why I thought there was a 12-minute time span betweenthe time of the shot and LAN for the DR longitude.  I converted his DR longitudeof 68d 25' to time, and got 4h + 32m + 100s, or 16:33:40.  I figured thatmeant that the sun would be over his meridian at that time.  The shot was madeat 16:46:20, which is 12m and 40s later.  Did I go wrong on that reasoning? Didthe navigator make his shot when he did, rather than when I would have advisedhim to had he asked me, simply because he recognized that his DR was not likelyto be close enough to make the difference significant?   Or, as another reader suggested, was this perhaps meant to be an"ex-meridian" sight?  In that case, as I eventually found in JeffToghill's "Celestial Navigation," the observed altitude should becorrected for the time difference by factors found in Bowditch.
(The tablesreferred to were 29 and 30, though in the 2002 Bowditch they are now 24 and 25.) I plan to rework the problem from that perspective and see what I get.Thanks again for your patience and thoroughness.  This list is like havingdozens of expert tutors on call!John

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