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From: Sean C
"A few days ago, I decided to do a random check. I set the time and date in my spreadsheet to 00:00:00 UT1, March 30th, 2025. Everything looked good until I got to Venus. My spreadsheet gives a GHA of 192°00.9', but the N.A. gives 192°00.5'."

It's a matter of center of mass (which an ephemeris gives) vs. center of light. My Lunar program has an option to compute the latter. (The option is disabled unless you select body center, not a limb, for altitude and distance.) I get 192°00.50' for geocentric apparent GHA, same as the Almanac.

This issue of center of mass vs. center of light came up recently as an issue [...*...]

The issue has been closed with satisfactory results. As I recall, the Huxtable formula is credited in the source code. It's the same formula I use.

I've helped the developers with some problems, such as pointing out the neglect of aberration corrections to star positions. However, I'm not involved in the coding. Nor have I attempted to steer the devopment of the plugin (except to object to angle output at 0.0001' precision).

--
Paul Hirose
sofajpl.com

[* As noted previously, discussion of the OpenCPN plugin belongs there, not here. -FER]