A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: William Porter
Date: 2018 Nov 1, 04:17 -0700
"Aha. Yet another step added to the process that makes it difficult to debug! :)" Yes, but that is where the bug is. And thank you again so much for helping me isolate it. I am calculating Altair's GHA wrong. That is a fundamental error. Being able to look it up right is no consolation. My aim here is to strip the whole thing back to basics that I understand; PZX triangles, HP*Cos(Hm) etc then rebuild it. If I wanted to rely on the work of others I would look up to the GPS (it's there, to be clear). It's not that I don't trust your work, NASA's etc, but in my "game" I want to be back there, with a reef to leeward and my then-new edition of Tabulae Motuum in front of me. This has to stop somewhere, I accept, and I currently use the lunar polynomials for Dec and RA. But given RA I need to convert to GHA. If there is a better way, PLEASE tell me but I am used to the GST ephemera and, better, I have an intuition for them and what they should be on any day. Bottom line, I want to build my own lunar-distance tables and/or replace the lunar GHAs that are no longer in the ephemera. So the question is, how am I going wrong between Altair's RA (the lunar RA proves out) and its (her?) GHA. Or, how better can I make the conversion?