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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Initial course nomogram
From: Frank Reed
Date: 2019 Oct 10, 11:16 -0700
From: Frank Reed
Date: 2019 Oct 10, 11:16 -0700
I believe that's the extended version of Weir's azimuth diagram. The azimuth of a celestial body is identical to the great circle "initial course" to the sub-star point (the GP). Diagrams like these were popular for celestial azimuths in the early 20th century but eventually they were superseded by simple one-entry table lookups. The Weir diagram in the auction item you found has been re-purposed for pure great circle work.
There's nothing wrong with using Weir's diagram(s) for celestial sights today, and the files below are examples which I used for some classes a couple of years ago. They are copied from Bennett's "Complete Onboard" tables. I'm also including an image of the Russian-language auction item for comparison.
Frank Reed
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