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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Frank Reed
Date: 2021 Nov 26, 10:54 -0800
Peter, you wrote:
"I was missing the division by the cosine of the declination in the SHA formula."
Ah yes. That happens frequently. I'm honestly surprised it didn't turn up as a problem sooner.
This still leaves the question: what specific values are you using for the proper motion in RA/SHA and Dec for Rigil Kentaurus (alpha Centauri)? The image below may help to illustrate the issue. The squiggly curves show the motions of the two stars of the system through 2050. The annual cusps are the stellar parallax loops. Since this star is so close and a binary, there is a substantial difference between the proper motion of the individual stars and the proper motion of the center of mass. So which should we use? The source article is from the journal Astronomy & Astrophysics vol. 594, October 2016: "Close stellar conjunctions of α Centauri A and B until 2050", authors: P. Kervella, F. Mignard, A. Mérand, and F. Thévenin [pdf].
Frank Reed
