NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Mark Coady
Date: 2015 Dec 3, 21:26 -0800
Sean,
I have it written in my notebook from my early days of reading everything in sight learning on my own.....I forget who I pilfered it from.
Checking it, I have an 1868 editon of Bowditch and if I go to the augmentation table it has a range of values from 0 augmentation @ 0 alt to 16 seconds augmentation @ 90 alt. (which =.2667 @ 90 degrees) (sin value of 1)
From there a check with the sin of the altitude say at 45 degrees: (bowditch augmentation 11 seconds=.183) (my filched formula .26 sin 45 =.184) so it matches within any rational quest the Bowditch table.
I note the Bowditch table is an approximation, Augmentation varies with a horizontal paralax, and the Bowditch table i believe is calculated on the average of HP @ about 57.7 HP which comes out to the .26 number which varies a bit with rounding.
My notes comment that actual augmentation factors vary from .299 at an HP of 61.4 to .230 @ at an HP 53.9'. (A min max scenario). which gives me an average of .26 by inspection (hence my use of it) Round to 1 decimal and back to old .3 agian.
Based on what we are doing in a lunar as I understand it, heck its close enough.
I recall the whole calculation is based on the 27.24% ratio SD to HP, and the factor of added size for the radius of the earth in NM 3438? (based on using the 21,600 circ.)
Someone cooked up a rule long ago that adds a bit of perspective on all my futzing with extra decimals.... Measure with a micrometer, Mark with chalk, Cut with an axe.......
