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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: David C
Date: 2018 Mar 29, 23:55 -0700
I have been using the Altitude Correction table from the 1973 NA. The reasons are that (a) I have a copy of the said NA and (b) the table is convenient, combining the semi-diameter and refraction corrections. When observing the sun is it valid to use the 1973 NA corrections in 2018?
I have noted small differences between the 1973 NA corrections and those in the 2018 Air Almanac. Is this because the Air Almanac is designed for observations with a bubble sextant and so a lower precision is used?
For the record I took a noonsight today and used Frank's lat = ZD + dec (zd -ve if shadow south) method. It was easy and less confusing than other methods I have used. When I measured the IE the sun's semi-diameter was only 25 arc seconds in error. However the latitude was off by a few nm which I put down to two reasons - problems with the AH and uncertainty over the refraction correction.
