NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Antoine Couëtte
Date: 2012 Apr 12, 22:44 -0700
> It's time to go to bed here in California, but my quick explanation for
> your anomaly: I think the IMCCE is using the IAU 1976 precession model.
Yes, Paul
I remember now that the Astronomer in charge of the IMCCE Server told me that they had not updated their Precession model. It is quite likely that their former model was the IAU 1976 Precession model. Interestingly enough, this IAU 1976 model coming into effect as of Jan 01, 1984, was shown in the very early 80's by my Friend late Dr. Pierre Bretagnon (VSOP80, VSOP82, VSOP87,SMART Nutation/Precession theories ...) to be quite inaccurate outside a few centuries from 2000 because one second order term (or third order term - I do not remember now and should check that in my archives -) included a quite significant and very sizable error. Pierre Bretagnon's views were eventually fully endorsed since by the IAU and led to the development of new models, with P03 being the most accurate one available to-day to cover a time span of +/- 10 000 years around year 2000.
*******
ON 10 Apr 2012, you wrote :
> Some precession models are optimized for the present time, plus or minus
> a few centuries, and should be used with caution at remote epochs. For
> example, before 500 AD the IAU 1976 model is more accurate than the IAU
> 2000 model. Both are less accurate than the 2006 model. (I compared all
> three models to a new long term model published [A&A 534, A22 (2011)]
> last year.)
Yes again, that is exactly that. Some Precession models are more accurate than others, with IAU 2006 model being the best one currently available. To the best of my understanding the "IAU 2006 Precession model" is one other name given to the "P03 Precession model" established by the French further to the outstanding development work pioneered by Pierre Bretagnon with his VSOPxx / SMART theories.
A last short story now :
VSOP = Variations Séculaires des Orbites Planétaires
SMART = Solution du Mouvement de l'Axe de Rotation Terrestre
JASON = Jupiter and Saturn Orbits through Neolithic
and a few more ....
In addition to be a Genius Astronomer equivalent to the great Urbain Le Verrier and Simon Newcomb, Pierre was also EXCELLENT at finding and inventing awesome acronyms ...
*******
And, as a final consequence, it is very likely that IMMCCE has not updated its Precession model on its Web Server, which in turn gives (quite) wrong results in some remote epochs, such a 2000 years back from now in the examples I mentioned to them one year ago and which I relayed to everybody's attention on NavList 2 days ago.
... Standing by for further comments from your part, and Thanks again for all your very valiable insights
Best Regards
Kermit
Antoine M. "Kermit" Couëtte
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