Starry Night Pro, nor thier "subject matter expert" community, has answered my question on how they calculate the ancient Earth's pole. So I just posted the following follow-up question on their forum ... see the thread here <[support.simulationcurriculum.com];
Hi All, Here is a further clarification of my question:
My version of Starry Night Pro (6.4.3) shows Vega culminating North at a declination of 86.2407 degrees, 12008 BC. The discrepancy is that I calculate Vega culminating North at declination 86.54 degrees, 12070 BC. I use the obliquity and precession model published by A.L. Berger (1976. Obliquity and Precession for the last 5,000,000 years. Astron. & Astrophys. 51, 127-135). I think that has become a standard calculation method used, for example, by climate change modelers, and considered relatively accurate especially for the recent past (last precession cycle or so). The difference between my value and Starry Night's value (for the declination) is not due to our very slightly different proper motions. Starry Night quotes a proper motion for Vega (0.2008, 0.2872) (RA,Dec) arcsec/year. The current SIMBAD website quoted values are (0.20094, 0.28623) [same units]. I used (0.20103, 0.28747) which was at the time the SIMBAD quoted value. That is clearly not the issue because those differences in proper motion yield less than 0.002 degrees differences over 14,000 years. (Compared to the 1.36 degrees movement of the whole proper motion itself.) The ΔT calculation can not be the source of the different culmination declinations (about 0.3 degrees difference). That difference is due to the calculated orientation of Earth’s pole. My question is how does Starry Night Pro calculate Earth’s pole during that epoch (circa 12,000 BC)?