A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Antoine Couëtte
Date: 2011 Feb 2, 10:23 -0800
[NavList] 2011 Nautical Almanac
Date: 1 Feb 2011 11:04
2011 Nautical Almanac
For some cases the accuracy may differ with respect the USNO NA.
But could be useful.
Attached File: 115541.2011_nautical_almanac.pdf (no thumbnail available)
Thank you for providing us with this beautifully arranged 2011 NAUTICAL ALMANAC. Its published Data certainly are very well laid out and displayed. CONGRATULATIONS to its Author.
I could not prevent then from visiting the advertising site :
which promotes its own ASTRONAV Software(both free and purchased version), and I can read among other features :
"AstroNav’s accuracy is measured in fractions of an arc-second and contains a comprehensive list of stars visible with binoculars. (Mag 10/ 330,000 stars.) It will produce better results than tables by avoiding their inherent simplifications. (0’.5 is possible)"
The Almanac screen can be used to produce conventional Nautical Almanac pages for any date between 9999 BC to 9999 AD. These can be used as backup or reference.
Information about Moon Phases and Eclipses is also available between 9999 BC and 9999 AD
Just a few questions about this AstroNav Software in general and about the 2011 NA in particular :
1 - Which theory/theories is such Software based on ? I am just curious here since I do not know of any Theories (whether Analytical Theories or Numerical Integrations) being accurate to "fractions of an arc-second" over such a 20K year period [9999BC-9999AD], especially for the Moon and the outer Planets,
2 - Is there anywhere any indication about the TT-UT values retained for the computations, at least in the past? TT-UT values amount to many hours well inside the specified time-frame [9999BC-9999AD] and certainly need to be known to the Users. The influence of TT-UT on the Celestial Bodies apparent positions, and in particular the Moon, is immense. And in a few hundred of years from now in the future, we all know that any TT-UT predicted value can only be speculative by nature.
3 - Which Precession parameters are being used ? Over such an important time span [9999BC-9999AD], the differences between various Precession models become quite significant when dealing with sub-arcsecond accuracies. The new recent IAU2000 P03 precession results differ from the previous IAU Precession model results by more than 1" in AD0000, by more than 3" in 2000BC, and by more than 8" in 9999BC.
4 - For the Moon, which Tidal Acceleration has been retained ? Outside the [1000AD-3000AD] time-frame, our current (2008) knowledge on the Moon Tidal Acceleration uncertainty (+/- 0.5"/cent**2 at the best) certainly becomes the main unknown parameter for the Moon Position (in)accuracy. Such Tidal Acceleration Parameter is also very difficult to accurately determine and single out since its overall "slowing down" effects also add up to the TT-UT effects.
5 - For our current Period, I have spot checked some of the data published in your 2011 NA and found ALL OF THEM to be accurate to better than 6"/.1 arc minute. So I am a bit surprised at your remark that "For some cases the accuracy may differ with respect the USNO NA." Why did you feel interesting/important to mention this point to our attention ?
Any more detailed insights you can provide here would be quite helpful.
Thanks again for your Kind Attention and
Antoine M. "Kermit" Cou�tte
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