A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: H.O. 249, Vol. 1 as a guide for star selection for direct position computation?
From: Greg Rudzinski
Date: 2017 Oct 2, 11:59 -0700
249 Selected Stars shows 7 stars with the optimal three stars marked with a black diamond above the star name. If selecting two stars then go with the pair that has azimuths differing by 90°.
From: Tony Oz
Date: 2017 Oct 2, 10:20 -0700
I'm experimenting with direct position computation.
The idea to do three successive sights and interpolate the 1st and 3rd altitudes to the moment of the 2nd sight (and then calculating the D12, A, B, Lat, LHA for that particular moment) seems productive - provided the bodies are selected properly.
I see that if I select something just ~20° apart (GHA-wise) - the longitude is obtained with a rather biggish error.
What is the optimum angular distance between the two bodies for the better position accuracy? How relevant are the suggested star pairs listed in the H.O.249 vol I (normally used for Intercepts) for direct position computation? How should I select what I take sight of?
Thank you in advance.
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