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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Jim Hickey
Date: 2025 Sep 12, 07:28 -0700
Just to recap, I was looking for a simple algorithm, suitable for use on a programmable calculator (my hp 15C) to calculate GHA and dec of the sun for 2025. Out of curiosity, I tried Copilot to see what it could do. I cut and paste the Copilot results into the attached Word document [pdf added].
The equation for JD works but the result given in the worked example does not agree with what I get when I put the equation in Excel. My Excel result for JD doe agree with Alex's equation of the NASA JD calculator. As for the rest of the equations, I do not get the same results as the worked example or correct GHA and dec using alternate time tried programs. They are sort of close but definitely not correct and not what I get when I put all the equations in Excel. It does not seem to be a degree/radians issue.
Cheers,
J
