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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Andrés Ruiz
Date: 2022 Sep 14, 15:00 +0200
Hello Brian,
Thanks for sharing.
After a very quick reading, some thoughts.
The paper deals with two different things: Bris sextant and Sight Reduction method.
Bris sextant
I've built dozens of Bris sextants, it is a lot of fun to make, calibrate and use afterwards. I have used welding glass 12, I think that shade-5 could be harmful to our eyes.
Declination
In your example you assume that Dec = cte and that the observer is stationary.
dDec/dt
14/09/2022 10:30:36 3º 19.9'
14/09/2022 13:16:59 3º 17.2'
20/10/2022 13:16:59 -10º 26.9'
20/10/2022 10:30:36 -10º 24.5'
20/10/2022
10:30:36 UT1
Sun derivatives
dDec/dt = -0.014922 º/h = -0.9 '/h = -0.00 '/s
dGHA/dt = 15.001708 º/h = 900.1 '/h = 0.25 '/s
And in your simulation Dec(-25, +25), looks weird.
Latitude
Seems that you use a variation of “Latitude by doble altitudes an elapsed time”, or Douwes, (Chauvenet 211, Pg 315), where Latitude = f(t1, Dec1, Ho1, t2, Dec2, Ho2) or Latitude = f(t1, Dec1, Ho1, t2, Dec2, Ho2, DR_latitude)
Longitude
If dDec/dt and dB/dt, dL/dt, (MOO motion of the observer), are negligible the altitude/time curve is symmetrical with respect to the meridian passage. Otherwise the error could be important.
Fix
Using a Bris I always use the MSH intercept method.
For example one of the simplest ways to obtain the position is: “Celestial Fix - 2 LoP analytic solution“ available at https://sites.google.com/site/navigationalalgorithms/Home/papersnavigation, that takes into account for Running fix.
Fair winds.
Link added:
I thought some folks might find this interesting. I published a method for calculating latitude using a Bris sextant in the Journal of Navigation. I would, of course, appreciate comments, questions, or criticism. If one of you were one of the reviewers, well, I suppose this isn't new to you!
https://www.academia.edu/85642586/Determination_of_latitude_by_two_fixed_altitude_sightings
