NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: I need help with my first noon sun sight
From: Jim Thompson
Date: 2003 Dec 20, 17:39 -0400
From: Jim Thompson
Date: 2003 Dec 20, 17:39 -0400
Ker-plunk! Everything dropped into place after interpolating EqT, Trevor. Thanks. http://jimthompson.net/boating/CelestialNav/NoonSunSight.htm Jim Thompson jim2@jimthompson.net www.jimthompson.net Outgoing mail scanned by Norton Antivirus ----------------------------------------- > -----Original Message----- > From: Navigation Mailing List > [mailto:NAVIGATION-L@LISTSERV.WEBKAHUNA.COM]On Behalf Of Trevor J. > Kenchington > > Explaining the difference between your Methods 1 & 2 is easy. For Method > 2, you started from the time of meridian passage quoted in the almanac > to the nearest minute. You cannot expect calculations based on that to > be accurate to anything better than the nearest minute. Since both of > your calculations round to a time of 1308, they are in full agreement to > this level of accuracy. If you want the time of meridian passage to > the nearest second, you can't use your Method 2. > > I think that your problem with your method 8 is that you have read off > the Equation of Time for 1200 GMT on 14 September but you are applying > it to an observation after 1600 GMT that day. If you check the almanac, > you will see that the Equation of Time increased by 10 seconds in the 12 > hours after 1200 GMT. Hence, in the four hours to your local noon, it > must have increased by 4 seconds (to the nearest second). Apply that > correction and your Method 8 will agree with your Method 1 to the > nearest second. > > You wrote: > > > Please see my calculations below for 3 ways to predict the > local zone time > > for meridian transit of the sun on September 14, 2003 at my > position of L > > 46o 11.1' N, Lo 63o 08.0' W (GPS Fix). I cannot understand why > Methods 1, 2 > > and 8 produce different predictions. Can anyone spot the reason? > > > > I made a time diagram of this problem, though I am not sure that it is > > correct, and it gives yet a third answer: > > http://jimthompson.net/boating/CelestialNav/NoonSunSight.htm#Time%20Diagram > (ignore the rest of what I have written on that page -- I am still muddling > through this).
