A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Antoine Couëtte
Date: 2010 Apr 3, 10:16 -0700
Super-great !!! You just had me discovering and enjoying an additionnal way of fully independently clearing Lunars and deriving Observer's positions without the recourse to the "2 Body Method".
Congratulations on that one, and again congratulations for your superb and user-friendly On Line Computer.
Also, regarding your comment on delta-T, you just wrote :
It really is quite un-necessary to specify delta-T in these historical analyses. While there remains some moderate uncertainty in the value of delta-T in the late 18th century (and that will not change unless some vast store of accurate astronomical observations from that period is found in archives somewhere), the values are known with enough certainty for any navigational calculations.
I am very sorry to keep itching some of us while "I keep publishing every single time the delta-T value I am using".
The bottom line is : if we use Modern Theories to process historical observations - which both of us are doing - are these values required ?
I would think that the answer is definitely "YES" *** , or at least the knowledge of delta-T used in the computations from Modern Theories is (somewhat / marginally) desirable - although incidentally (maybe not after all ... ) of little numerical significance just for our period of Lunars - and,
- although you think that they are not a "variable" per se - which I also agree to a great extent because these values are rather small during our Lunars Period - you also and almost most probably use them in your On-Line Computer.
However, and just and only for our potential Number Crunching addicts - and I am aware of a few of them -, and although these dela-T values are not strictly necessary given their small amplitude just for the period of our Lunars (full agreement between us on this point) I am just publishing the delta-T values I have used here simply because :
- I am not sure that they are widely available everywhere and anywhere yet,
- they are still subject to some uncertainty, and will likely remain so indefinitely, which means different Number Crunchers can use different delta-T values, and
- it is better "in principle" (or certainly "not worse") to use them to convert the TT scale "INTO" our currently best reconstruction of UT rather than to deliberately keep using TT "INSTEAD OF" UT while discarting such readily available values which have required so many huge efforts to reconstruct from historical data.
Unless this current reply is grossly in error, or unless I totally and wrongly misinterpreted your last Posting - which I would highly regret and apologise for immediately - I think it better now to consider that the "delta-T" subject is a closed issue between all of us, for fear of continuing to bother all other NavList Members with these matters. What would be your opinion here ?
If anybody has any private opinion on this, I will certainly and kindly listen to any comment here : antoine.m.couette at club.fr. If such opinion is to be made public, then no problem, thanks again to Frank, we have this superb NavList Forum.
Again your On Line Computer is absolutely superb, very clerverly though and designed, and this is and by far the MOST IMPORTANT point to all of us, including and definitely to the writer and undersigner of these lines.
Please accept my very Best Regards
Antoine M. "Kermit" Couëtte
*** if the answer were "NO" ... then I will need to attend Navigation Lectures in a most reputable well-known place in the USA. :-)
NavList message boards and member settings: www.fer3.com/NavList
Members may optionally receive posts by email.
To cancel email delivery, send a message to NoMail[at]fer3.com