A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Antoine Couëtte
Date: 2017 Dec 27, 10:52 -0800
RE : EdPopko-dec-2017-g41040
Thank you for your very kind feedback in EdPopko-dec-2017-g41039 and EdPopko-dec-2017-g41040.
In my last post (Couëtte-dec-2017-g41041) following yours referenced here-above, I should have mentioned that neither the Oblateness of Earth nor the Refractional Flattening of the Moon have any sizeable effect on the final results of your specific Aldebaran-Moon Lunar initially published in EdPopko-dec-2017-g41011 . This fact can be verified through Frank's calculator, as you will get exactly the same results with or without Oblateness and/or Flattening.
Still referring to my last post (Couëtte-dec-2017-g41041), I should have also added that - according to Frank's Calculator - your sextant error of 0.0333' ( 0.2 ") is equivalent to a clock error of only 0.4 seconds of time. Whaooo !!!
This needs be compared with your own computational determination of a 32 second clock error for the very same Aldebaran-Moon Lunar as indicated at the very end of EdPopko-dec-2017-g41011 .
I do not think that we should be overly "shocked" at such a difference magnitude between both results simply because your own 32 second clock error result amounts to a computational "error" of [only] 0.267 ' on the Sextant Arc. Maybe this 0.3' value lies at the [very] high end of an acceptable computational error magnitude given the simple numerical method you have been using onto your HP Calculator. Assuming that Frank's On Line Calculator is "perfect" in this regard - and we really have every reason to think that it is - and provided that you have not done any computational blunder - maybe worth rechecking ? - only Frank could tell us whether a difference between both methods amounting to 0.267' in a final Lunar Distance determination is an acceptable difference or is not.
As I have already observed differences of up to this order of Magnitude (0.3') between Frank's Calculator results and other "traditional classical" Methods - and I have also programmed one of them (by Jean Charles, Chevalier de Borda I think) in addition to my much better and "bigger" Lunar Sofware - I have come to the conclusion that, when compared to any and all Classical Computational Methods Frank's Calculator is a far superior tool in terms of results overall reliability and accuracy when dealing with classical lunars such as this one. Assuming "perfect" Ephemeris at hand, I do not know of any Classical Computational Method accurate to perform better than 9" under all Classical Lunars cases. They all have a "gap in the net" somewhere, not in the same areas though, and that's probably why we have so many of them. Frank's Computer simply does not show any gap in Classical Lunars, at least from what I have been able to see and verify so many times until now.
I have devised my own "bigger" Lunar software from a starting point totally different from anything published before whatsoever, this last statement being to the best of my knowledge. I am therefore in a fully independent position to see that, for classical Lunars (not Occultations), Frank's Calculator - and especially through the advocated iterative method such as the example shown in Couëtte-dec-2017-g41041 - is an extremely reliable and deadly accurate performing tool. Frank's Calculator angular determinations never differ from mine by more than 3" or exceptionnaly 4", which I strongly suspect comes mainly because I am using a Lunar Ephemeris Software accurate to only 4" or better, which is already almost an overkill for our traditional Sextant Work. I understand here that Frank's Calculator works with the JPL full series which are deemed to be accurate to almost a zillionth of an arcsecond. No way for me to compete with such an awesome accuracy figure. Nonetheless, below a 3" or 4" accuracy figure, the Moon edge shape as seen from the Earth with its very visible mountains definitely starts playing in a very significant manner. Hence a hand held very long term (over 1.000 years both ways from Year 2000.0) Moon Ephemeris accurate to 4" or better is already an excellent and superb tool for our Traditional Lunars, especially when we deal with Sextant Work.
Back to our topic, and from a totally independent computing tool, I can only confirm and praise Frank's On Line Lunar Computer (http://reednavigation.com/lunars/lunars_v4.html) results as being extremely reliable and accurate at the sub 0.1' arc level as detailed here-above and as advertised.
To recap, Lunars are lots of fun, aren't they, even when they drive you into some tedious Detective Work :-) true, Ed ?
Thanks again, Ed, for this wonderful opportunity you offered us to tackle another Lunar.
Best Friendly Regards,
Antoine M. Couëtte