NavList:

Jim Hickey wrote in his original message in this conversation that he had asked for:
  "A simple algorithm to determine the GHA and declination of the sun for 2025"

None of you who replied asked why he needed a detailed Julian Date calculation. Or did that come up, and I missed it?? Even if we extend the requested time period to the end of 2026, a running day count is trivial --especially since the next leap year is not until 2028. And of course for any modern app (without interest in historical cases), the inclusion of the long-term century rules for leap years is completely un-necessary. So suppose you just want a running JD-"like" day count for the next 12 months, what code will work?

Or, maybe even more interesting, set aside all these modern machines and their A.I. Overlords... Ask instead: what human computation method could you use to generate a running day count (something more clever than the "brute force" of making a list of days in every elapsed month and then adding them up)? A common use case would be generating GHA Aries "in your head" by working out 98.56% of day count from September 21 (any year). 

Jim Hickey, I may have missed it, but it appears that you didn't actually tell us what equation MS Copilot gave you for JD calculation. Could you do that? Without that, no one can comment intelligently on what may have gone wrong! ...Right? :)

Frank Reed